Ok, here is the explanation what happens.
When starting up, the spi-imx.c driver calls a function to register the SPI controller. This function parses the device tree and collects all GPIO chip select numbers in an array. Then when the function returns, the driver calls gpio_request() for each entry in the array so that all these GPIOs can be used as chip selects afterwards.
However the above function does much more than just collecting GPIO numbers. It also parses all sub-nodes in the SPI device tree node and creates a device for each of them. This actually leads to a call of function spi_imx_setup() for each device which is used to set the GPIO direction of the appropriate chip select to output. But as you can see, this happens *before* the original function returns to the probe function, where the GPIOs are requested. So the sequence, that a GPIO must be requested first before it can be used, is violated.
On GPIO1, where other drivers already requested some GPIOs, this nonetheless works because the clock to this GPIO block is already active from the other GPIOs. But on GPIO3, where no other GPIOs are requested by other drivers, this fails because the clock is still off when the output direction should be set. The clock is only activated later by the gpio_request() call.
This made it quite difficult to locate the problem. Of course I immediately thought of the clocks, but after the probe function, when the system is running, the clock to GPIO3 was active, too. So at first I did not understand at all why only the accesses to GPIO3 fail. It needed quite a lot of debug output and many many tries to understand that the clock is still off at the point of time when the GPIO direction is set.
The attached patch will move the gpio_request() from the probe function to function spi_imx_setup(). This fixes the call sequence.
Go to the Linux kernel source directory and call
Please note the less-than character '<' to redirect the input.
Then recompile and reinstall the kernel. Now everything should work as expected. Sorry for the inconvenience.
Your F&S Support Team