i.mx8QuadPlus imx-rpmsg_tty driver does not get probed

[nlbutts]

We have a custom Yocto build based on the 5.4.70 Yocto release. In U-boot I am able to load and start the M4 process and get the following message from the serial port:

RPMSG String Echo FreeRTOS RTOS API Demo...

I then try to load the imx_rpmsg_tty driver in Linux by doing the following:

insmod /lib/modules/5.4.70+g5ca957774d45/kernel/drivers/rpmsg/imx_rpmsg_tty.ko

I never received any messages in the kernel log, so I added a print statement in the init function of the imx_rpmsg_tty.c file. Now when I insmod the driver I get the print statement, but the probe function is not called. 

static int __init init(void)
{
    printk("NLB imx_rpmmsg_tty\n");
	return register_rpmsg_driver(&rpmsg_tty_driver);
}

I do see the imx_rpmsg driver registered on bootup:

[    0.079095] imx rpmsg driver is registered.
[    0.721916] mmcblk0rpmb: mmc0:0001 S0J35A partition 3 4.00 MiB, chardev (239:0)
[   58.720062] NLB imx_rpmmsg_tty
[  158.781342] NLB imx_rpmmsg_tty

But I don't see the imx_rpmsg_tty device in the dev nodes (/dev). I suspect it has something to do with the device tree. I do have memory reserved. I have also tried to set the rpmsg node to okay:

&rpmsg{
	/*
	 * 64K for one rpmsg instance:
	 */
	vdev-nums = <2>;
	reg = <0x0 0x90000000 0x0 0x20000>;
	memory-region = <&vdevbuffer>;
	status = "okay";
};

When I do that I get an error with the imx_rpmsg driver:

[    0.079195] imx rpmsg driver is registered.
[    0.723292] mmcblk0rpmb: mmc0:0001 S0J35A partition 3 4.00 MiB, chardev (239:0)
[    1.006545] imx-rpmsg: probe of 90000000.rpmsg failed with error -16

When I look through the imx_rpmsg driver, it has references to sound stuff. Can anyone point me in the right direction?

[AldoG]

Hello,

Please try with modprobe instead of insmod, i.e.
$ modprobe imx_rpmsg_tty

After this you may check if the module installed by using lsmod.

Best regards,
Aldo.

[nlbutts]

The same result occurs after running modprobe imx_rpmsg_tty.

Output of DMESG:

[    5.237891] systemd[1]: system-getty.slice: unit configures an IP firewall, but the local system does not support BPF/cgroup firewalling.
[    5.250295] systemd[1]: (This warning is only shown for the first unit using IP firewalling.)
[    5.261730] systemd[1]: Created slice system-getty.slice.
[    5.280802] systemd[1]: Created slice system-serial\x2dgetty.slice.
[    5.300669] systemd[1]: Created slice User and Session Slice.
[    6.085989] systemd-journald[287]: Received client request to flush runtime journal.
[    7.206992] [VPU Encoder] enable mu for core[0]
[    7.220616] [VPU Encoder] vpu encoder core[0] firmware version is 1.3.0
[    7.276604] atmel_mxt_ts 16-004a: mxt_start:  Starting . . .
[    7.423597] atmel_mxt_ts 16-004a: mxt_stop:  Stopping . . .
[    9.123410] fsl-audmix 59840000.amix: Started TDM1 needed for config propagation!
[   18.948057] audit: type=1006 audit(1638305278.216:2): pid=405 uid=0 old-auid=4294967295 auid=0 tty=(none) old-ses=4294967295 ses=1 res=1
[   19.535593] audit: type=1006 audit(1638305278.804:3): pid=402 uid=0 old-auid=4294967295 auid=0 tty=(none) old-ses=4294967295 ses=2 res=1

Looking at /dev shows no ttyRPMSG node:

autofs           gpiochip3        iio:device7      mmcblk0          ptyp3            seco_mu1_ch3     tty11            tty29            tty46            tty63            ttypa            vcsa3
block            gpiochip4        iio:device8      mmcblk0boot0     ptyp4            seco_mu2_ch0     tty12            tty3             tty47            tty7             ttypb            vcsa4
bus              gpiochip5        iio:device9      mmcblk0boot1     ptyp5            seco_mu2_ch1     tty13            tty30            tty48            tty8             ttypc            vcsa5
caam-keygen      gpiochip6        initctl          mmcblk0p1        ptyp6            seco_mu2_ch2     tty14            tty31            tty49            tty9             ttypd            vcsa6
char             gpiochip7        input            mmcblk0p2        ptyp7            seco_mu2_ch3     tty15            tty32            tty5             ttyLP0           ttype            vcsu
console          gpiochip8        ion              mmcblk0rpmb      ptyp8            seco_mu3_ch0     tty16            tty33            tty50            ttyS0            ttypf            vcsu1
cpu_dma_latency  hugepages        kmsg             mqueue           ptyp9            seco_mu3_ch1     tty17            tty34            tty51            ttyS1            ubi_ctrl         vcsu2
cuse             hwrng            kvm              mxc_asrc         ptypa            seco_mu3_ch2     tty18            tty35            tty52            ttyS2            urandom          vcsu3
disk             i2c-16           log              mxc_hifi4        ptypb            seco_mu3_ch3     tty19            tty36            tty53            ttyS3            v4l              vcsu4
dri              iio:device0      loop-control     net              ptypc            secvio-sc        tty2             tty37            tty54            ttyp0            vcs              vcsu5
fb0              iio:device1      loop0            null             ptypd            shm              tty20            tty38            tty55            ttyp1            vcs1             vcsu6
fd               iio:device10     loop1            port             ptype            snd              tty21            tty39            tty56            ttyp2            vcs2             vfio
fsl-usdpaa-irq   iio:device11     loop2            pps0             ptypf            stderr           tty22            tty4             tty57            ttyp3            vcs3             vga_arbiter
full             iio:device12     loop3            ptmx             random           stdin            tty23            tty40            tty58            ttyp4            vcs4             vhci
fuse             iio:device2      loop4            ptp0             rtc              stdout           tty24            tty41            tty59            ttyp5            vcs5             video12
galcore          iio:device3      loop5            pts              rtc0             tty              tty25            tty42            tty6             ttyp6            vcs6             video13
gpiochip0        iio:device4      loop6            ptyp0            seco_mu1_ch0     tty0             tty26            tty43            tty60            ttyp7            vcsa             watchdog
gpiochip1        iio:device5      loop7            ptyp1            seco_mu1_ch1     tty1             tty27            tty44            tty61            ttyp8            vcsa1            watchdog0
gpiochip2        iio:device6      mem              ptyp2            seco_mu1_ch2     tty10            tty28            tty45            tty62            ttyp9            vcsa2            zero

[AldoG]

Hi,

This may be caused by how are you loading and starting the Cortex-M4, for i.MX8QM, SCU_ROM will handle the load of M4 binary code. SCU will create a seperate resource partition(generally partition 3) and based on that partition, there would be resource isolation(including memory region) between M core and A core.

To flash your own M4 image, please follow SDK doc "Getting Started with MCUXpresso SDK for MEK-MIMX8QM" - "Run a demo using imx-mkimage".You need to build a flash.bin file with M4 by imx-mkimage, using "make SOC=iMX8QM flash_linux_m4"

Please try it and let me now of your results.

Best regards,
Aldo.

[nlbutts]

I've tried many different ways to get the M4 up and running. This has been an extremely painful process. I've used the i.MX Linux Reference manual dated 30 Sept 2021. I've also used the AN5317 app note. But there are many gaps in the explanation of how things work. I've tried the following:

1) Get SCFW to load the M4. I was never able to get this working no matter what I tried.

2) Get u-boot to load the M4. I was able to get the M4 loaded and running. But as soon as u-boot loaded the Kernel but prior to it actually transferring control, it appears to stop the M4. 

3) Get Linux to load the M4. This works and is the method I am pursing. 

For one boot cycle I was able to get the /dev/ttyRPMSG30 to show up. But now I can't get it to work. It must be some sort of order of operations. Currently I have systemd loading the imx_rpmsg_tty.ko via /etc/modules.d.

Then I have a script that loads the M4 firmware later on. The M4 starts up and I see it register the RPMSG interface. But a /dev/ttyRPMSG dev node never shows up, so I can't communicate with the M4. 

[nlbutts]

Ah, it seems the kernel module has to be loaded AFTER the M4 code is running. This is horribly broken. Why can't I load the kernel module first!!!