About SPI and dma from Linux user space

[Eldam]

Hello ST People !

I'm looking for information / possiblity to use SPI (via spidev & ioctl) in Linux user space with DMA.

We have to transfert lots of data (4000bytes at one time, very very often) to a fpga, very quickly and we are facing latency issue during transfert.

With the help of a scope, we see dead times between spi transactions during this big packet write.

So we are thinking using spi dma to unload cpu, but we need some infos/direction to look for.

Maybe someone help or points me to right direction?

Bon weekend!

[Eldam]

After looking at:

https://github.com/torvalds/linux/blob/master/drivers/spi/spi-stm32.c

If I "lsmod" on my board, I see that "spi_stm32" is in the lsmod list.

So If I understand correctly,

If I made call to ioctl (with /dev/spidev0.0 as parameter)

the ioctl function will use the "spi_stm32" driver mod? Thats it?

How do we know if we already or not using dma?

(we have dts enabled dma for spi tree)

[Eldam · Accepted solution]

Well, after a little struggling

With the help of:

https://wiki.st.com/stm32mpu/wiki/SPI_overview

We added kernel debug info and we happy to see:

"dma enabled" in the log file.

so with some modification of calling function (ioctl) we've been able to have a 12Mhz SPI working @ 12Mbits /s

Next phase, modify the clk!

Seeya!