On Thu, Mar 19, 2015 at 01:28:00PM -0400, 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 You probably need both - there's often a hard limit where the FIFO size in the hardware becomes a limit for DMA as well as a soft limit on top of that for performance reasons. > 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? Exposing it as a sysfs or debugfs file might make more sense if you were going to do this. Is that required after merge though? It seems like this is something where we've perhaps been tuning the wrong parameter (transfer size instead of runtime), or need to investigate dynamic tuning.
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