[qemu] Implement `opentitantool` qemu transport

[moidx]

Description

Implement QEMU transport compatible with Earlgrey 1.0.0. The transport should support the following interfaces:

• P1 - UART Console
• P1 - SPI Console
• P1 - SPI bootstrap
• P1 - JTAG
• P1 - GPIO (prioritize provisioning use cases - i.e. straps, reset, GPIO toggle)
• P1 - SPI boot services
• P2 - USB
• P2 - I2C

[moidx]

The team has started working on scoping options for this. @amit-kumarh will follow up with @cfrantz to discuss the opens raised by @nbdd0121 and @jwnrt.

[jwnrt]

Update: I have UART and reset working on my local branch and I'll start SPI next.

[jwnrt]

For GPIO I think the current chardev is connected directly to the GPIO block rather than via pinmux as expected by OpenTitanLib. We will need a new chardev going via the pinmux for full support, but there's also a chance we can support provisioning flows with the direct-to-gpio interface.

[jwnrt]

I’ve merged #28291 which has support for the UART console and resetting.

[jwnrt]

I have the SPI interface working in #28353 and the flash test passing, but I want to get the console working before it’s merged.

That should unblock work on the QEMU side to implement the TPM and passthrough modes.

[jwnrt]

The current status of each interface is:

• UART: UART console working, others are easily added but lower priority.
• SPI: flash working (PR pending). Console WIP, TPM and passthrough require QEMU changes. Bootstrap depends on GPIO.
• GPIO: RESET working, straps might be possible with only OpenTitanTool changes, generic pinmux requires QEMU changes.
• I2C: protocol defined on QEMU side, waiting on OpenTitanTool support.
• JTAG: QEMU supports RV_DM, LC_CTRL needs porting from Darjeeling. OpenTitanTool changes are relatively simple.
• USB: Amaury is scoping work on QEMU side, expecting non-trivial USB-IP implementation. OpenTitanTool side is expected to be easier.

[jwnrt]

Ah, I wasn't aware that the SPI console uses GPIO. I think I'll work on GPIO next to unblock bootstrapping, SPI console, and potentially JTAG strapping.