Re: Patch to parameterize DMA_MIN_BYTES for omap2-mcspi

[Greg Knight <g.knight@xxxxxxxxxxxxx>]

> I think the best thing we could do is to calculate the DMA_MIN_BYTES
in the
> driver based on the SPI speed. Something which will give ~160 in the
speed in
> which the wl driver is used and something which works best in your
setup in
> the speed you are using the SPI bus.
> The best way is to give some msec as a limit. If the transfer would
take more
> then X msec on the bus to be transferred, we will use DMA, if it is
less than
> that we fall back to PIO.
> Yes, the CPU speed is not taken into account, but IMHO the bus speed
is more
> 

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?

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

Regards,
Greg

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