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AM335x McSPI chip select not deasserting

Thomas Jupe
Prodigy 30 points


Hi,

I'm working on a custom board with an AM335x processor and running a Buildroot system on it based on the first dozen pages of this tutorial: http://free-electrons.com/doc/training/buildroot/buildroot-labs.pdf. So the kernel version is 4.6 and looking at the kernel menuconfig reveals that the only drivers selected under SPI support are McSPI driver for OMAP and User mode SPI device driver support.

I've enabled userspace access to the the SPI drivers so our software can do SPI transactions from userspace.


What I'm seeing though, is that after I do an SPI transaction the chip select line stays low until I do an operation on another device (another chip select line). That line then also stays low. and this happens on all the SPI lines.


I did not get this behaviour while doing the same SPI transactions using a system based on a rootfs from a debian image for beaglebone: bone-debian-8.1-console-armhf-2015-08-31-2gb.img.


I am currently looking at potential differences between the drivers, but has anyone else experienced something similar and know how to remedy it?

Thanks,


Thomas