Skip to content

Latest commit

 

History

History
996 lines (700 loc) · 40.7 KB

porting-guide.md

File metadata and controls

996 lines (700 loc) · 40.7 KB
Raw

ARM Trusted Firmware Porting Guide

Contents

  1. Introduction
  2. Common Modifications
    • Common mandatory modifications
    • Common optional modifications
  3. Boot Loader stage specific modifications
    • Boot Loader stage 1 (BL1)
    • Boot Loader stage 2 (BL2)
    • Boot Loader stage 3-1 (BL3-1)
    • PSCI implementation (in BL3-1)
  4. C Library
  1. Introduction

Porting the ARM Trusted Firmware to a new platform involves making some mandatory and optional modifications for both the cold and warm boot paths. Modifications consist of:

  • Implementing a platform-specific function or variable,
  • Setting up the execution context in a certain way, or
  • Defining certain constants (for example #defines).

The firmware provides a default implementation of variables and functions to fulfill the optional requirements. These implementations are all weakly defined; they are provided to ease the porting effort. Each platform port can override them with its own implementation if the default implementation is inadequate.

Some modifications are common to all Boot Loader (BL) stages. Section 2 discusses these in detail. The subsequent sections discuss the remaining modifications for each BL stage in detail.

This document should be read in conjunction with the ARM Trusted Firmware User Guide.

  1. Common modifications

This section covers the modifications that should be made by the platform for each BL stage to correctly port the firmware stack. They are categorized as either mandatory or optional.

2.1 Common mandatory modifications

A platform port must enable the Memory Management Unit (MMU) with identity mapped page tables, and enable both the instruction and data caches for each BL stage. In the ARM FVP port, each BL stage configures the MMU in its platform- specific architecture setup function, for example blX_plat_arch_setup().

Each platform must allocate a block of identity mapped secure memory with Device-nGnRE attributes aligned to page boundary (4K) for each BL stage. This memory is identified by the section name tzfw_coherent_mem so that its possible for the firmware to place variables in it using the following C code directive:

__attribute__ ((section("tzfw_coherent_mem")))

Or alternatively the following assembler code directive:

.section tzfw_coherent_mem

The tzfw_coherent_mem section is used to allocate any data structures that are accessed both when a CPU is executing with its MMU and caches enabled, and when it's running with its MMU and caches disabled. Examples are given below.

The following variables, functions and constants must be defined by the platform for the firmware to work correctly.

File : platform.h [mandatory]

Each platform must export a header file of this name with the following constants defined. In the ARM FVP port, this file is found in ../plat/fvp/platform.h.

  • #define : PLATFORM_LINKER_FORMAT

    Defines the linker format used by the platform, for example elf64-littleaarch64 used by the FVP.

  • #define : PLATFORM_LINKER_ARCH

    Defines the processor architecture for the linker by the platform, for example aarch64 used by the FVP.

  • #define : PLATFORM_STACK_SIZE

    Defines the normal stack memory available to each CPU. This constant is used by platform_set_stack().

  • #define : FIRMWARE_WELCOME_STR

    Defines the character string printed by BL1 upon entry into the bl1_main() function.

  • #define : BL2_IMAGE_NAME

    Name of the BL2 binary image on the host file-system. This name is used by BL1 to load BL2 into secure memory using semi-hosting.

  • #define : PLATFORM_CACHE_LINE_SIZE

    Defines the size (in bytes) of the largest cache line across all the cache levels in the platform.

  • #define : PLATFORM_CLUSTER_COUNT

    Defines the total number of clusters implemented by the platform in the system.

  • #define : PLATFORM_CORE_COUNT

    Defines the total number of CPUs implemented by the platform across all clusters in the system.

  • #define : PLATFORM_MAX_CPUS_PER_CLUSTER

    Defines the maximum number of CPUs that can be implemented within a cluster on the platform.

  • #define : PRIMARY_CPU

    Defines the MPIDR of the primary CPU on the platform. This value is used after a cold boot to distinguish between primary and secondary CPUs.

  • #define : TZROM_BASE

    Defines the base address of secure ROM on the platform, where the BL1 binary is loaded. This constant is used by the linker scripts to ensure that the BL1 image fits into the available memory.

  • #define : TZROM_SIZE

    Defines the size of secure ROM on the platform. This constant is used by the linker scripts to ensure that the BL1 image fits into the available memory.

  • #define : TZRAM_BASE

    Defines the base address of the secure RAM on platform, where the data section of the BL1 binary is loaded. The BL2 and BL3-1 images are also loaded in this secure RAM region. This constant is used by the linker scripts to ensure that the BL1 data section and BL2/BL3-1 binary images fit into the available memory.

  • #define : TZRAM_SIZE

    Defines the size of the secure RAM on the platform. This constant is used by the linker scripts to ensure that the BL1 data section and BL2/BL3-1 binary images fit into the available memory.

  • #define : SYS_CNTCTL_BASE

    Defines the base address of the CNTCTLBase frame of the memory mapped counter and timer in the system level implementation of the generic timer.

  • #define : BL2_BASE

    Defines the base address in secure RAM where BL1 loads the BL2 binary image. Must be aligned on a page-size boundary.

  • #define : BL31_BASE

    Defines the base address in secure RAM where BL2 loads the BL3-1 binary image. Must be aligned on a page-size boundary.

Other mandatory modifications

The following mandatory modifications may be implemented in any file the implementer chooses. In the ARM FVP port, they are implemented in ../plat/fvp/aarch64/plat_common.c.

  • Variable : unsigned char platform_normal_stacks[X][Y]

    where  X = PLATFORM_STACK_SIZE
  and  Y = PLATFORM_CORE_COUNT

    Each platform must allocate a block of memory with Normal Cacheable, Write back, Write allocate and Inner Shareable attributes aligned to the size (in bytes) of the largest cache line amongst all caches implemented in the system. A pointer to this memory should be exported with the name platform_normal_stacks. This pointer is used by the common platform helper functions platform_set_stack() (to allocate a stack for each CPU in the platform) & platform_get_stack() (to return the base address of that stack) (see ../plat/common/aarch64/platform_helpers.S).

2.2 Common optional modifications

The following are helper functions implemented by the firmware that perform common platform-specific tasks. A platform may choose to override these definitions.

Function : platform_get_core_pos()

Argument : unsigned long
Return   : int

A platform may need to convert the MPIDR of a CPU to an absolute number, which can be used as a CPU-specific linear index into blocks of memory (for example while allocating per-CPU stacks). This routine contains a simple mechanism to perform this conversion, using the assumption that each cluster contains a maximum of 4 CPUs:

linear index = cpu_id + (cluster_id * 4)

cpu_id = 8-bit value in MPIDR at affinity level 0
cluster_id = 8-bit value in MPIDR at affinity level 1

Function : platform_set_coherent_stack()

Argument : unsigned long
Return   : void

A platform may need stack memory that is coherent with main memory to perform certain operations like:

  • Turning the MMU on, or
  • Flushing caches prior to powering down a CPU or cluster.

Each BL stage allocates this coherent stack memory for each CPU in the tzfw_coherent_mem section. A pointer to this memory (pcpu_dv_mem_stack) is used by this function to allocate a coherent stack for each CPU. A CPU is identified by its MPIDR, which is passed as an argument to this function.

The size of the stack allocated to each CPU is specified by the constant PCPU_DV_MEM_STACK_SIZE.

Function : platform_is_primary_cpu()

Argument : unsigned long
Return   : unsigned int

This function identifies a CPU by its MPIDR, which is passed as the argument, to determine whether this CPU is the primary CPU or a secondary CPU. A return value of zero indicates that the CPU is not the primary CPU, while a non-zero return value indicates that the CPU is the primary CPU.

Function : platform_set_stack()

Argument : unsigned long
Return   : void

This function uses the platform_normal_stacks pointer variable to allocate stacks to each CPU. Further details are given in the description of the platform_normal_stacks variable below. A CPU is identified by its MPIDR, which is passed as the argument.

The size of the stack allocated to each CPU is specified by the platform defined constant PLATFORM_STACK_SIZE.

Function : platform_get_stack()

Argument : unsigned long
Return   : unsigned long

This function uses the platform_normal_stacks pointer variable to return the base address of the stack memory reserved for a CPU. Further details are given in the description of the platform_normal_stacks variable below. A CPU is identified by its MPIDR, which is passed as the argument.

The size of the stack allocated to each CPU is specified by the platform defined constant PLATFORM_STACK_SIZE.

Function : plat_report_exception()

Argument : unsigned int
Return   : void

A platform may need to report various information about its status when an exception is taken, for example the current exception level, the CPU security state (secure/non-secure), the exception type, and so on. This function is called in the following circumstances:

  • In BL1, whenever an exception is taken.
  • In BL2, whenever an exception is taken.
  • In BL3-1, whenever an asynchronous exception or a synchronous exception other than an SMC32/SMC64 exception is taken.

The default implementation doesn't do anything, to avoid making assumptions about the way the platform displays its status information.

This function receives the exception type as its argument. Possible values for exceptions types are listed in the ../include/runtime_svc.h header file. Note that these constants are not related to any architectural exception code; they are just an ARM Trusted Firmware convention.

  1. Modifications specific to a Boot Loader stage

3.1 Boot Loader Stage 1 (BL1)

BL1 implements the reset vector where execution starts from after a cold or warm boot. For each CPU, BL1 is responsible for the following tasks:

  1. Distinguishing between a cold boot and a warm boot.

  2. In the case of a cold boot and the CPU being the primary CPU, ensuring that only this CPU executes the remaining BL1 code, including loading and passing control to the BL2 stage.

  3. In the case of a cold boot and the CPU being a secondary CPU, ensuring that the CPU is placed in a platform-specific state until the primary CPU performs the necessary steps to remove it from this state.

  4. In the case of a warm boot, ensuring that the CPU jumps to a platform- specific address in the BL3-1 image in the same processor mode as it was when released from reset.

  5. Loading the BL2 image in secure memory using semi-hosting at the address specified by the platform defined constant BL2_BASE.

  6. Populating a meminfo structure with the following information in memory, accessible by BL2 immediately upon entry.

    meminfo.total_base = Base address of secure RAM visible to BL2
meminfo.total_size = Size of secure RAM visible to BL2
meminfo.free_base  = Base address of secure RAM available for
                     allocation to BL2
meminfo.free_size  = Size of secure RAM available for allocation to BL2

    BL1 places this meminfo structure at the beginning of the free memory available for its use. Since BL1 cannot allocate memory dynamically at the moment, its free memory will be available for BL2's use as-is. However, this means that BL2 must read the meminfo structure before it starts using its free memory (this is discussed in Section 3.2).

    In future releases of the ARM Trusted Firmware it will be possible for the platform to decide where it wants to place the meminfo structure for BL2.

    BL1 implements the init_bl2_mem_layout() function to populate the BL2 meminfo structure. The platform may override this implementation, for example if the platform wants to restrict the amount of memory visible to BL2. Details of how to do this are given below.

The following functions need to be implemented by the platform port to enable BL1 to perform the above tasks.

Function : platform_get_entrypoint() [mandatory]

Argument : unsigned long
Return   : unsigned int

This function is called with the SCTLR.M and SCTLR.C bits disabled. The CPU is identified by its MPIDR, which is passed as the argument. The function is responsible for distinguishing between a warm and cold reset using platform- specific means. If it's a warm reset then it returns the entrypoint into the BL3-1 image that the CPU must jump to. If it's a cold reset then this function must return zero.

This function is also responsible for implementing a platform-specific mechanism to handle the condition where the CPU has been warm reset but there is no entrypoint to jump to.

This function does not follow the Procedure Call Standard used by the Application Binary Interface for the ARM 64-bit architecture. The caller should not assume that callee saved registers are preserved across a call to this function.

This function fulfills requirement 1 listed above.

Function : plat_secondary_cold_boot_setup() [mandatory]

Argument : void
Return   : void

This function is called with the MMU and data caches disabled. It is responsible for placing the executing secondary CPU in a platform-specific state until the primary CPU performs the necessary actions to bring it out of that state and allow entry into the OS.

In the ARM FVP port, each secondary CPU powers itself off. The primary CPU is responsible for powering up the secondary CPU when normal world software requires them.

This function fulfills requirement 3 above.

Function : platform_cold_boot_init() [mandatory]

Argument : unsigned long
Return   : unsigned int

This function executes with the MMU and data caches disabled. It is only called by the primary CPU. The argument to this function is the address of the bl1_main() routine where the generic BL1-specific actions are performed. This function performs any platform-specific and architectural setup that the platform requires to make execution of bl1_main() possible.

The platform must enable the MMU with identity mapped page tables and enable caches by setting the SCTLR.I and SCTLR.C bits.

Platform-specific setup might include configuration of memory controllers, configuration of the interconnect to allow the cluster to service cache snoop requests from another cluster, zeroing of the ZI section, and so on.

In the ARM FVP port, this function enables CCI snoops into the cluster that the primary CPU is part of. It also enables the MMU and initializes the ZI section in the BL1 image through the use of linker defined symbols.

This function helps fulfill requirement 2 above.

Function : bl1_platform_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches enabled. It is responsible for performing any remaining platform-specific setup that can occur after the MMU and data cache have been enabled.

In the ARM FVP port, it zeros out the ZI section, enables the system level implementation of the generic timer counter and initializes the console.

This function helps fulfill requirement 5 above.

Function : bl1_plat_sec_mem_layout() [mandatory]

Argument : void
Return   : meminfo *

This function should only be called on the cold boot path. It executes with the MMU and data caches enabled. The pointer returned by this function must point to a meminfo structure containing the extents and availability of secure RAM for the BL1 stage.

meminfo.total_base = Base address of secure RAM visible to BL1
meminfo.total_size = Size of secure RAM visible to BL1
meminfo.free_base  = Base address of secure RAM available for allocation
                     to BL1
meminfo.free_size  = Size of secure RAM available for allocation to BL1

This information is used by BL1 to load the BL2 image in secure RAM. BL1 also populates a similar structure to tell BL2 the extents of memory available for its own use.

This function helps fulfill requirement 5 above.

Function : init_bl2_mem_layout() [optional]

Argument : meminfo *, meminfo *, unsigned int, unsigned long
Return   : void

Each BL stage needs to tell the next stage the amount of secure RAM available for it to use. For example, as part of handing control to BL2, BL1 informs BL2 of the extents of secure RAM available for BL2 to use. BL2 must do the same when passing control to BL3-1. This information is populated in a meminfo structure.

Depending upon where BL2 has been loaded in secure RAM (determined by BL2_BASE), BL1 calculates the amount of free memory available for BL2 to use. BL1 also ensures that its data sections resident in secure RAM are not visible to BL2. An illustration of how this is done in the ARM FVP port is given in the User Guide, in the Section "Memory layout on Base FVP".

3.2 Boot Loader Stage 2 (BL2)

The BL2 stage is executed only by the primary CPU, which is determined in BL1 using the platform_is_primary_cpu() function. BL1 passed control to BL2 at BL2_BASE. BL2 executes in Secure EL1 and is responsible for:

  1. Loading the BL3-1 binary image in secure RAM using semi-hosting. To load the BL3-1 image, BL2 makes use of the meminfo structure passed to it by BL1. This structure allows BL2 to calculate how much secure RAM is available for its use. The platform also defines the address in secure RAM where BL3-1 is loaded through the constant BL31_BASE. BL2 uses this information to determine if there is enough memory to load the BL3-1 image.

  2. Arranging to pass control to a normal world BL image that has been pre-loaded at a platform-specific address. This address is determined using the plat_get_ns_image_entrypoint() function described below.

    BL2 populates an el_change_info structure in memory provided by the platform with information about how BL3-1 should pass control to the normal world BL image.

  3. Populating a meminfo structure with the following information in memory that is accessible by BL3-1 immediately upon entry.

    meminfo.total_base = Base address of secure RAM visible to BL3-1
meminfo.total_size = Size of secure RAM visible to BL3-1
meminfo.free_base  = Base address of secure RAM available for allocation
                     to BL3-1
meminfo.free_size  = Size of secure RAM available for allocation to
                     BL3-1

    BL2 places this meminfo structure in memory provided by the platform (bl2_el_change_mem_ptr). BL2 implements the init_bl31_mem_layout() function to populate the BL3-1 meminfo structure described above. The platform may override this implementation, for example if the platform wants to restrict the amount of memory visible to BL3-1. Details of this function are given below.

The following functions must be implemented by the platform port to enable BL2 to perform the above tasks.

Function : bl2_early_platform_setup() [mandatory]

Argument : meminfo *, void *
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU. The arguments to this function are:

  • The address of the meminfo structure populated by BL1
  • An opaque pointer that the platform may use as needed.

The platform must copy the contents of the meminfo structure into a private variable as the original memory may be subsequently overwritten by BL2. The copied structure is made available to all BL2 code through the bl2_plat_sec_mem_layout() function.

Function : bl2_plat_arch_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU.

The purpose of this function is to perform any architectural initialization that varies across platforms, for example enabling the MMU (since the memory map differs across platforms).

Function : bl2_platform_setup() [mandatory]

Argument : void
Return   : void

This function may execute with the MMU and data caches enabled if the platform port does the necessary initialization in bl2_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to perform any platform initialization specific to BL2. This function must initialize a pointer to memory (bl2_el_change_mem_ptr), which can then be used to populate an el_change_info structure. The underlying requirement is that the platform must initialize this pointer before the get_el_change_mem_ptr() function accesses it in bl2_main().

The ARM FVP port initializes this pointer to the base address of Secure DRAM (0x06000000).

Variable : unsigned char bl2_el_change_mem_ptr[EL_CHANGE_MEM_SIZE] [mandatory]

As mentioned in the description of bl2_platform_setup(), this pointer is initialized by the platform to point to memory where an el_change_info structure can be populated.

Function : bl2_plat_sec_mem_layout() [mandatory]

Argument : void
Return   : meminfo *

This function should only be called on the cold boot path. It may execute with the MMU and data caches enabled if the platform port does the necessary initialization in bl2_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to return a pointer to a meminfo structure populated with the extents of secure RAM available for BL2 to use. See bl2_early_platform_setup() above.

Function : init_bl31_mem_layout() [optional]

Argument : meminfo *, meminfo *, unsigned int
Return   : void

Each BL stage needs to tell the next stage the amount of secure RAM that is available for it to use. For example, as part of handing control to BL2, BL1 must inform BL2 about the extents of secure RAM that is available for BL2 to use. BL2 must do the same when passing control to BL3-1. This information is populated in a meminfo structure.

Depending upon where BL3-1 has been loaded in secure RAM (determined by BL31_BASE), BL2 calculates the amount of free memory available for BL3-1 to use. BL2 also ensures that BL3-1 is able reclaim memory occupied by BL2. This is done because BL2 never executes again after passing control to BL3-1. An illustration of how this is done in the ARM FVP port is given in the User Guide, in the section "Memory layout on Base FVP".

Function : plat_get_ns_image_entrypoint() [mandatory]

Argument : void
Return   : unsigned long

As previously described, BL2 is responsible for arranging for control to be passed to a normal world BL image through BL3-1. This function returns the entrypoint of that image, which BL3-1 uses to jump to it.

The ARM FVP port assumes that flash memory has been pre-loaded with the UEFI image, and so returns the base address of flash memory.

3.2 Boot Loader Stage 3-1 (BL3-1)

During cold boot, the BL3-1 stage is executed only by the primary CPU. This is determined in BL1 using the platform_is_primary_cpu() function. BL1 passes control to BL3-1 at BL31_BASE. During warm boot, BL3-1 is executed by all CPUs. BL3-1 executes at EL3 and is responsible for:

  1. Re-initializing all architectural and platform state. Although BL1 performs some of this initialization, BL3-1 remains resident in EL3 and must ensure that EL3 architectural and platform state is completely initialized. It should make no assumptions about the system state when it receives control.

  2. Passing control to a normal world BL image, pre-loaded at a platform- specific address by BL2. BL3-1 uses the el_change_info structure that BL2 populated in memory to do this.

  3. Providing runtime firmware services. Currently, BL3-1 only implements a subset of the Power State Coordination Interface (PSCI) API as a runtime service. See Section 3.3 below for details of porting the PSCI implementation.

The following functions must be implemented by the platform port to enable BL3-1 to perform the above tasks.

Function : bl31_early_platform_setup() [mandatory]

Argument : meminfo *, void *, unsigned long
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU. The arguments to this function are:

  • The address of the meminfo structure populated by BL2.
  • An opaque pointer that the platform may use as needed.
  • The MPIDR of the primary CPU.

The platform must copy the contents of the meminfo structure into a private variable as the original memory may be subsequently overwritten by BL3-1. The copied structure is made available to all BL3-1 code through the bl31_plat_sec_mem_layout() function.

Function : bl31_plat_arch_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU.

The purpose of this function is to perform any architectural initialization that varies across platforms, for example enabling the MMU (since the memory map differs across platforms).

Function : bl31_platform_setup() [mandatory]

Argument : void
Return   : void

This function may execute with the MMU and data caches enabled if the platform port does the necessary initialization in bl31_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to complete platform initialization so that both BL3-1 runtime services and normal world software can function correctly.

The ARM FVP port does the following:

  • Initializes the generic interrupt controller.
  • Configures the CLCD controller.
  • Grants access to the system counter timer module
  • Initializes the FVP power controller device
  • Detects the system topology.

Function : bl31_get_next_image_info() [mandatory]

Argument : unsigned long
Return   : el_change_info *

This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup().

This function is called by bl31_main() to retrieve information provided by BL2, so that BL3-1 can pass control to the normal world software image. This function must return a pointer to the el_change_info structure (that was copied during bl31_early_platform_setup()).

Function : bl31_plat_sec_mem_layout() [mandatory]

Argument : void
Return   : meminfo *

This function should only be called on the cold boot path. This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to return a pointer to a meminfo structure populated with the extents of secure RAM available for BL3-1 to use. See bl31_early_platform_setup() above.

3.3 Power State Coordination Interface (in BL3-1)

The ARM Trusted Firmware's implementation of the PSCI API is based around the concept of an affinity instance. Each affinity instance can be uniquely identified in a system by a CPU ID (the processor MPIDR is used in the PSCI interface) and an affinity level. A processing element (for example, a CPU) is at level 0. If the CPUs in the system are described in a tree where the node above a CPU is a logical grouping of CPUs that share some state, then affinity level 1 is that group of CPUs (for example, a cluster), and affinity level 2 is a group of clusters (for example, the system). The implementation assumes that the affinity level 1 ID can be computed from the affinity level 0 ID (for example, a unique cluster ID can be computed from the CPU ID). The current implementation computes this on the basis of the recommended use of MPIDR affinity fields in the ARM Architecture Reference Manual.

BL3-1's platform initialization code exports a pointer to the platform-specific power management operations required for the PSCI implementation to function correctly. This information is populated in the plat_pm_ops structure. The PSCI implementation calls members of the plat_pm_ops structure for performing power management operations for each affinity instance. For example, the target CPU is specified by its MPIDR in a PSCI CPU_ON call. The affinst_on() handler (if present) is called for each affinity instance as the PSCI implementation powers up each affinity level implemented in the MPIDR (for example, CPU, cluster and system).

The following functions must be implemented to initialize PSCI functionality in the ARM Trusted Firmware.

Function : plat_get_aff_count() [mandatory]

Argument : unsigned int, unsigned long
Return   : unsigned int

This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup(). It is only called by the primary CPU.

This function is called by the PSCI initialization code to detect the system topology. Its purpose is to return the number of affinity instances implemented at a given affinity level (specified by the first argument) and a given MPIDR (specified by the second argument). For example, on a dual-cluster system where first cluster implements 2 CPUs and the second cluster implements 4 CPUs, a call to this function with an MPIDR corresponding to the first cluster (0x0) and affinity level 0, would return 2. A call to this function with an MPIDR corresponding to the second cluster (0x100) and affinity level 0, would return 4.

Function : plat_get_aff_state() [mandatory]

Argument : unsigned int, unsigned long
Return   : unsigned int

This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup(). It is only called by the primary CPU.

This function is called by the PSCI initialization code. Its purpose is to return the state of an affinity instance. The affinity instance is determined by the affinity ID at a given affinity level (specified by the first argument) and an MPIDR (specified by the second argument). The state can be one of PSCI_AFF_PRESENT or PSCI_AFF_ABSENT. The latter state is used to cater for system topologies where certain affinity instances are unimplemented. For example, consider a platform that implements a single cluster with 4 CPUs and another CPU implemented directly on the interconnect with the cluster. The MPIDRs of the cluster would range from 0x0-0x3. The MPIDR of the single CPU would be 0x100 to indicate that it does not belong to cluster 0. Cluster 1 is missing but needs to be accounted for to reach this single CPU in the topology tree. Hence it is marked as PSCI_AFF_ABSENT.

Function : plat_get_max_afflvl() [mandatory]

Argument : void
Return   : int

This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup(). It is only called by the primary CPU.

This function is called by the PSCI implementation both during cold and warm boot, to determine the maximum affinity level that the power management operations should apply to. ARMv8-A has support for 4 affinity levels. It is likely that hardware will implement fewer affinity levels. This function allows the PSCI implementation to consider only those affinity levels in the system that the platform implements. For example, the Base AEM FVP implements two clusters with a configurable number of CPUs. It reports the maximum affinity level as 1, resulting in PSCI power control up to the cluster level.

Function : platform_setup_pm() [mandatory]

Argument : plat_pm_ops **
Return   : int

This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup(). It is only called by the primary CPU.

This function is called by PSCI initialization code. Its purpose is to export handler routines for platform-specific power management actions by populating the passed pointer with a pointer to BL3-1's private plat_pm_ops structure.

A description of each member of this structure is given below. Please refer to the ARM FVP specific implementation of these handlers in ../plat/fvp/plat_pm.c as an example. A platform port may choose not implement some of the power management operations. For example, the ARM FVP port does not implement the affinst_standby() function.

plat_pm_ops.affinst_standby()

Perform the platform-specific setup to enter the standby state indicated by the passed argument.

plat_pm_ops.affinst_on()

Perform the platform specific setup to power on an affinity instance, specified by the MPIDR (first argument) and affinity level (fourth argument). The state (fifth argument) contains the current state of that affinity instance (ON or OFF). This is useful to determine whether any action must be taken. For example, while powering on a CPU, the cluster that contains this CPU might already be in the ON state. The platform decides what actions must be taken to transition from the current state to the target state (indicated by the power management operation).

plat_pm_ops.affinst_off()

Perform the platform specific setup to power off an affinity instance in the MPIDR of the calling CPU. It is called by the PSCI CPU_OFF API implementation.

The MPIDR (first argument), affinity level (second argument) and state (third argument) have a similar meaning as described in the affinst_on() operation. They are used to identify the affinity instance on which the call is made and its current state. This gives the platform port an indication of the state transition it must make to perform the requested action. For example, if the calling CPU is the last powered on CPU in the cluster, after powering down affinity level 0 (CPU), the platform port should power down affinity level 1 (the cluster) as well.

This function is called with coherent stacks. This allows the PSCI implementation to flush caches at a given affinity level without running into stale stack state after turning off the caches. On ARMv8-A cache hits do not occur after the cache has been turned off.

plat_pm_ops.affinst_suspend()

Perform the platform specific setup to power off an affinity instance in the MPIDR of the calling CPU. It is called by the PSCI CPU_SUSPEND API implementation.

The MPIDR (first argument), affinity level (third argument) and state (fifth argument) have a similar meaning as described in the affinst_on() operation. They are used to identify the affinity instance on which the call is made and its current state. This gives the platform port an indication of the state transition it must make to perform the requested action. For example, if the calling CPU is the last powered on CPU in the cluster, after powering down affinity level 0 (CPU), the platform port should power down affinity level 1 (the cluster) as well.

The difference between turning an affinity instance off versus suspending it is that in the former case, the affinity instance is expected to re-initialize its state when its next powered on (see affinst_on_finish()). In the latter case, the affinity instance is expected to save enough state so that it can resume execution by restoring this state when its powered on (see affinst_suspend_finish()).

This function is called with coherent stacks. This allows the PSCI implementation to flush caches at a given affinity level without running into stale stack state after turning off the caches. On ARMv8-A cache hits do not occur after the cache has been turned off.

plat_pm_ops.affinst_on_finish()

This function is called by the PSCI implementation after the calling CPU is powered on and released from reset in response to an earlier PSCI CPU_ON call. It performs the platform-specific setup required to initialize enough state for this CPU to enter the normal world and also provide secure runtime firmware services.

The MPIDR (first argument), affinity level (second argument) and state (third argument) have a similar meaning as described in the previous operations.

This function is called with coherent stacks. This allows the PSCI implementation to flush caches at a given affinity level without running into stale stack state after turning off the caches. On ARMv8-A cache hits do not occur after the cache has been turned off.

plat_pm_ops.affinst_on_suspend()

This function is called by the PSCI implementation after the calling CPU is powered on and released from reset in response to an asynchronous wakeup event, for example a timer interrupt that was programmed by the CPU during the CPU_SUSPEND call. It performs the platform-specific setup required to restore the saved state for this CPU to resume execution in the normal world and also provide secure runtime firmware services.

The MPIDR (first argument), affinity level (second argument) and state (third argument) have a similar meaning as described in the previous operations.

This function is called with coherent stacks. This allows the PSCI implementation to flush caches at a given affinity level without running into stale stack state after turning off the caches. On ARMv8-A cache hits do not occur after the cache has been turned off.

BL3-1 platform initialization code must also detect the system topology and the state of each affinity instance in the topology. This information is critical for the PSCI runtime service to function correctly. More details are provided in the description of the plat_get_aff_count() and plat_get_aff_state() functions above.

  1. C Library

To avoid subtle toolchain behavioral dependencies, the header files provided by the compiler are not used. The software is built with the -nostdinc flag to ensure no headers are included from the toolchain inadvertently. Instead the required headers are included in the ARM Trusted Firmware source tree. The library only contains those C library definitions required by the local implementation. If more functionality is required, the needed library functions will need to be added to the local implementation.

Versions of FreeBSD headers can be found in include/stdlib. Some of these headers have been cut down in order to simplify the implementation. In order to minimize changes to the header files, the FreeBSD layout has been maintained. The generic C library definitions can be found in include/stdlib with more system and machine specific declarations in include/stdlib/sys and include/stdlib/machine.

The local C library implementations can be found in lib/stdlib. In order to extend the C library these files may need to be modified. It is recommended to use a release version of FreeBSD as a starting point.

The C library header files in the FreeBSD source tree are located in the include and sys/sys directories. FreeBSD machine specific definitions can be found in the sys/<machine-type> directories. These files define things like 'the size of a pointer' and 'the range of an integer'. Since an AArch64 port for FreeBSD does not yet exist, the machine specific definitions are based on existing machine types with similar properties (for example SPARC64).

Where possible, C library function implementations were taken from FreeBSD as found in the lib/libc directory.

A copy of the FreeBSD sources can be downloaded with git.

git clone git://github.com/freebsd/freebsd.git -b origin/release/9.2.0

Copyright (c) 2013-2014, ARM Limited and Contributors. All rights reserved.