How to use spi-loopback-test linux kernel module?

user_1641819 0
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I do not understand how to use the linux kernel module spi-loopback-test.

This module is compiled from spi-loopback-test.c, and is still maintained.
It was created for SPI regression test purpose (see initial commit log), but there is not documentation nor instruction anywhere on the net.

  1. I am able to compile and load the module, but nothing happens when it is loaded.
    No message in dmesg, no activity on the physical SPI buses. lsmod shows the module is loaded.

  2. It seems like the module's spi_loopback_test_probe function is never called.
    I think I am missing some "glue" (DT overlay??) in the Device Tree, to assign a physical SPI port to the module.
    How to assign a SPI port to this module?
    Should I create a DT overlay to add a spi-loopback-test driver node under the existing spi0 peripheral node?

  3. Also, I noticed the module parameter compatible that can changed before loading.
    What value could be set here?

My target system is a Raspberry Pi 4B (but I guess the issue is generalisable to all linux systems).

Any help/pointer is appreciated!
Thanks

spi raspberry-pi linux-kernel module linux
1 Answers

Okay, I finally found one way to run the spi-loopback-test module.
The trick here was to use anyspi Device-Tree overlay, to avoid the dependency of spidev module.
I got my inspiration from this commit.

  1. First of all, the kernel must be recompiled to include the test feature “spi-loopback-test”.
    I followed this guide, cross-compiling from a Ubuntu VM.
  2. Enable SPI loopback module via “menuconfig” before compiling: CONFIG_SPI_DEBUG=y and CONFIG_SPI_LOOPBACK_TEST=m
  3. Load the kernel image and its device-tree onto the target system (RPi4).
  4. Run the following commands on the RPi4:
$ sudo dmesg -n 8

$ lsmod | grep spi

$ sudo dtoverlay anyspi spi0-1 dev="linux,spi-loopback-test" speed=125000000

$ lsmod | grep spi
spi_loopback_test      28672  0
spidev                 20480  0
spi_bcm2835            24576  0

$ dmesg | grep spi > spi-loopback-test.log

$ $ head spi-loopback-test.log -n 15
[   48.170758] OF: overlay: WARNING: memory leak will occur if overlay removed, property: /soc/spi@7e204000/spidev@1/status
[   48.170785] OF: overlay: WARNING: memory leak will occur if overlay removed, property: /soc/spi@7e204000/status
[   48.182921] spi-bcm2835 fe204000.spi: registered master spi0
[   48.183056] spi spi0.1: setup: forcing CS_HIGH (use_gpio_descriptors)
[   48.183075] spi spi0.1: setup mode 0, cs_high, 8 bits/w, 125000000 Hz max --> 0
[   48.183187] spi-bcm2835 fe204000.spi: registered child spi0.1
[   48.183217] spi spi0.0: setup: forcing CS_HIGH (use_gpio_descriptors)
[   48.183232] spi spi0.0: setup mode 0, cs_high, 8 bits/w, 125000000 Hz max --> 0
[   48.183327] spi-bcm2835 fe204000.spi: registered child spi0.0
[   48.269732] spi-loopback-test spi0.1: Executing spi-loopback-tests
[   48.269946] spi-loopback-test spi0.1: Running test tx/rx-transfer - start of page
[   48.270204] spi-loopback-test spi0.1:   with iteration values: len = 0, tx_off = 0, rx_off = 1
[   48.270431] spi-loopback-test spi0.1:   with iteration values: len = 0, tx_off = 0, rx_off = 2
[   48.270657] spi-loopback-test spi0.1:   with iteration values: len = 0, tx_off = 0, rx_off = 3
[   48.270883] spi-loopback-test spi0.1:   with iteration values: len = 0, tx_off = 1, rx_off = 0

$ tail spi-loopback-test.log
[   51.878516] spi-loopback-test spi0.1:   with iteration values: len = 1024, tx_off = 0, rx_off = 0
[   51.881159] spi-loopback-test spi0.1:   with iteration values: len = 1031, tx_off = 0, rx_off = 0
[   51.883826] spi-loopback-test spi0.1:   with iteration values: len = 4093, tx_off = 0, rx_off = 0
[   51.886892] spi-loopback-test spi0.1:   with iteration values: len = 4096, tx_off = 0, rx_off = 0
[   51.889950] spi-loopback-test spi0.1:   with iteration values: len = 4099, tx_off = 0, rx_off = 0
[   51.893862] spi-loopback-test spi0.1:   with iteration values: len = 65536, tx_off = 0, rx_off = 0
[   51.905280] spi-loopback-test spi0.1:   with iteration values: len = 65537, tx_off = 0, rx_off = 0
[   51.916708] spi-loopback-test spi0.1:   with iteration values: len = 131071, tx_off = 0, rx_off = 0
[   51.937417] spi-loopback-test spi0.1:   with iteration values: len = 131072, tx_off = 0, rx_off = 0
[   52.057851] spi-loopback-test spi0.1: Finished spi-loopback-tests with return: 0

So it looks like the SPI tests succeeded, as expected. Now I know a bit better how to interface the kernel modules to the hardware.
I hope this can be useful to somebody else too.

However, I wonder if there is a simpler solution to load and run this kernel module??
Can it be done without relying on anyspi DT overlay, by only setting the compatible parameter of spi-loopback-mode module?

user_16418190
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