Update PRU driver

[YuryMalyshev]

As stated in the provisioning.conf, uboot_overlay_pru is currently broken due to changes in the kernel.

However, it works fine in BeagleBoard's latest distro, AM335x 11.7 2023-09-02 4GB microSD IoT, which also uses kernel 5.10.
Here's my uEnv.txt:

uname_r=5.10.168-ti-r71
enable_uboot_overlays=1
uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-19-TI-00A0.dtbo
enable_uboot_cape_universal=1
console=ttyS0,115200n8
cmdline=coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100 quiet

The system starts up and it's possible to load a new firmware onto the PRU.

A similar config in Nerves breaks the system:

cmd("fw_setenv enable_uboot_overlays 1")
cmd("fw_setenv uboot_overlay_pru /lib/firmware/AM335X-PRU-RPROC-4-19-TI-00A0.dtbo")
cmd("fw_setenv enable_uboot_cape_universal 1")

Perhaps, it's necessary to use a different version of AM335X-PRU-RPROC-4-19-TI-00A0.dtbo?

Unfortunately, I'm not familiar with the topic enough to contribute anything else.

[fhunleth]

I'm currently not using the PRUs and haven't for years. They definitely did work with nerves_system_bbb at one time, but I think Linux or BeagleBoard changed how they wanted things to work and I got it wrong.

My memory is that there were two ways of interacting with the PRU. One is via UIO and the other is via RPROC. You found the RPROC way. The UIO way is to use AM335X-PRU-UIO-00A0.dtbo. Based on your report, I think that I got confused and thought that they were changing to UIO back when two ways were introduced. This was quite a long time ago.

I don't know if UIO is even viable for the PRUs these days, but if it is, I think it will work. I think that there are Linux device drivers that need to be enabled to support the AM335X-PRU-RPROC-4-19-TI-00A0.dtbo overlay. It's probably enabling one or two kernel options. I don't have access to a Linux machine this evening to poke around and take a guess. A good hint would be for you to run lsmod on the Beagleboard distro. I would expect kernel modules that have pru or rproc in their name to show up. Sorry about not having a better answer now. I'll should have access to a Linux machine next week.

[YuryMalyshev]

Thank you for the response!
As it stands, both AM335X-PRU-UIO-00A0.dtbo and AM335X-PRU-RPROC-4-19-TI-00A0.dtbo crash the Nerves system.

Here's the output of lsmod for 4 different configurations:
(Module order is listed as it was outputted. Dashes were used for clarity)

Default	RPROC	UIO	Working UIO
pru_rproc	pru_rproc	-	-
irq_pruss_intc	irq_pruss_intc	-	-
pm33xx	pm33xx	pm33xx	pm33xx
pruss	pruss	-	-
-	-	-	uio_pruss
-	pvrsrvkm	pvrsrvkm	pvrsrvkm
-	-	uio_pruss	-
ti_eqep	ti_eqep	ti_eqep	ti_eqep
counter	counter	counter	counter
c_can_platform	c_can_platform	c_can_platform	c_can_platform
c_can	c_can	c_can	c_can
can_dev	can_dev	can_dev	can_dev
evdev	evdev	evdev	evdev
wkup_m3_ipc	wkup_m3_ipc	wkup_m3_ipc	wkup_m3_ipc
uio_pdrv_genirq	uio_pdrv_genirq	uio_pdrv_genirq	uio_pdrv_genirq
uio	uio	uio	uio
cpufreq_dt	cpufreq_dt	cpufreq_dt	cpufreq_dt
spidev	spidev	spidev	spidev

The default configuration doesn't have uboot_overlay_pru at all.
"UIO" configuration doesn't seem to work - there are no uio devices under /dev/
The difference between "UIO" and "Working UIO" is the way uboot_overlay_pru is assigned:

UIO: uboot_overlay_pru=/lib/firmware/AM335X-PRU-UIO-00A0.dtbo
Working UIO: uboot_overlay_pru=AM335X-PRU-UIO-00A0.dtbo
RPROC is enabled via: uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-19-TI-00A0.dtbo