60MHz SPI on Colibri iMX8X

Technical Support
, , ,
1

One customer would like to use SPI master on Colibri iMX8X with 60MHz clock. Testing with spidev_test will meet following error:

root@colibri-imx8x:~# ./spidev_test -H -O -D /dev/spidev0.0 -s 60000000
spi mode: 3
bits per word: 8
max speed: 60000000 Hz (60000 KHz)
can't send spi message: Invalid argument
Aborted

root@colibri-imx8x:~# [  253.233858] fsl_lpspi 5a020000.lpspi: per-clk should be at least two times of transfer speed
[  253.243170] spidev spi0.0: SPI transfer failed: -22
[  253.248105] spi_master spi0: failed to transfer one message from queue
[  253.254917] audit: type=1701 audit(1583819358.812:5): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=3999 comm="spidev_test" exe="/home/root/spidev_test" sig=6 res=1

Search on NXP community, I find this thread. It says one has to modify SCU to generate required clock for SPI. So does customer have to build customer SCFW according to our page?

Thanks!

2

HI @benjamin.tx

You need to assign a different Parent Clock to the Spi Node.

Please have a look here.

Best regards,
Jaski

3

Additionally to the setting of the spi parent clock you have to note the off-by-one-error in the driver for calculating the prescaler of the spi output clock.

I achieved a maximum frequency of 58,2 MHz by setting the max speed to e.g. 50 MHz.

4

HI

Thanks for your Input.

Best regards,
Jaski

5

thanks @jaski.tx and @Mowlwurf , with Oleksandr’s patch it can work with 60MHz.

6

Hi @jaski.tx , I measure 60MHz SPI clock output on SODIMM 88 with a oscilloscope but the clock wave is quite bad. [upload|MEcCo7BTxFmS96XY25IvX0MspXA=]
In device tree, SC_P_SPI2_SCK_ADMA_SPI2_SCK is already set to 0x06000040. According to iMX8QXP RM (9.2.5.1.100 SPI2_SCK (SPI2_SCK)), last bit PDRV is 0b which meaning output is configured in High Drive mode both in 1.8 V and 3.3 V applications.
When an external 10k resistor is added to pull SPI2_SCK to 3.3V, the wave does not get better.
However, the oscilloscope’s max bandwidth is 200MHz, 60MHz is close to this limitation for a sufficient sample. I don’t have more advanced oscilloscope here. Could you help to check if 60MHz output wave is ok? Thanks!

10MHz SPI clock is good.
[upload|iUqp23HkGCBLbfOsfwc7o6LP5SQ=]