I’ve seen on multiple busses is that the MISO just outright doesn’t work in linux. We are using kernel 3.15 (boundary branch).
The behavior is (on and IMX6 quad plus):
SPI 4 appears to be fully functional. I am able to read/write and see all the data expected.
In linux, it seems to be writing, I see the data on a logic analyzer, however the MISO is just flat.
The CLK, SSO, and MOSI all seem to function properly.
This is using the same bit patterns as what is sent In U-Boot.
For ECSPI4 the device tree entries are as follow:
fsl,spi-num-chipselects = <1>;
cs-gpios = (&gpio3 20 GPIO_ACTIVE_LOW>;
pinctrl-names = “default”;
pinctrl-0 = &pinctrl_ecspi4>;
status = “okay”;
compatible = “spidev”;
spi-max-freuqnecy = <20000000>;
reg = <0>;
The above code I had to type out real quick (developed in VM on windows machine so I couldn’t copy/paste)
Weve also seen this issue on ECSPI2 where with a logic analyzer, we see the data being written out on the bus, but no reply