Issues with no MOSI data on spidev1.0 (c260000) on AGX Orin

[conradmenchine]

Hi all,
I'm trying to bring up the "spi2" bus on a ConnectTech Forge breakout board, which is spi@c260000 in the Orin device tree. I made a few tweaks to enable it:

spi@c260000{
		status = "okay";
		spi@0{
			reg = <0x00>;
			compatible = "tegra-spidev";
			interrupt-parent = <&tegra_main_gpio>;
			interrupts = <TEGRA234_MAIN_GPIO(A, 02) IRQ_TYPE_EDGE_FALLING>;

			controller-data {
				nvidia,enable-hw-based-cs;
				nvidia,rx-clk-tap-delay = <0x10>;
				nvidia,tx-clk-tap-delay = <0x00>;
			};
		};
	};

Now, /dev/spidev1.0 shows up, and I'm able to use spidev_test to dump data out of it. Strangely, though, it appears that only the CS and sCLK lines work. The MOSI stays low during this whole process.

My first thought was that there's something wrong with the pinmux, but I'm not even sure which spi instance in the pinmux corresponds to this one. It seems that some of the pinmux SPI instances default to "mosi" being an input/tristate (possible for SPI Slave mode?), but after changing every MOSI's pinmux to look identical to the first SPI instance I'm still seeing the same problem. Is this something that anyone else has dealt with before? Thanks!

[conradmenchine]

Update: After days of investigation, I've uncovered something very strange in /sys/kernel/debug/gpio:

 gpio-323 (PAA.07              )
 gpio-324 (PBB.00              )
 gpio-325 (PBB.01              )
 gpio-326 (PBB.02              )
 gpio-327 (PBB.03              )
 gpio-328 (PCC.00              )
 gpio-329 (PCC.01              )
 gpio-330 (PCC.02              |fixed-regulators:reg) out lo 
 gpio-331 (PCC.03              )
 gpio-332 (PCC.04              )

... And of course, PCC.02 is spi2 mosi. I added an extra line to disable the regulator and it fixed the issue.

	fixed-regulators {
		dsi_vdd_1v8_bl_en: regulator@116 {
			status = "disabled";
		};
	};

However, this still doesn't explain how/why this is happening. There's nothing special in my device tree that would cause this. Has anyone seen this?