Re: Patch to parameterize DMA_MIN_BYTES for omap2-mcspi

[Peter Ujfalusi <peter.ujfalusi-l0cyMroinI0@public.gmane.org>]

On 03/19/2015 07:28 PM, Greg Knight wrote:
> Changing DMA_MIN_BYTES to, say, "dma_min_time_ms" sounds reasonable to
> me. I don't know how to compute it completely accurately as some SPI
> implementations I've seen seem to like to inject little delays between
> bytes for some reason, but a reasonable enough estimate should just be
> spi_transfer_time_ms = (bits * 1000) / spi_clock_speed.
> 
> I would like to have the ability to configure it without a kernel
> recompile, though. Would a kernel param (module_param) be acceptable for
> this application?

Or sysfs interface as Mark suggested? But module_param should work as well.

> You don't happen to know the WL12xx SPI clock speed off the top of your
> head, do you?

In case of n900 it is 48000000 (board-rx51-peripherals.c). It is using 32bit
words over SPI.

Based on this and your experience I guess it is possible to come up with a
formula which satisfy both.

> Regards,
> Greg
> 


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