Messages in this thread | | | From | Jon Masters <> | Date | Mon, 3 Oct 2011 05:24:27 -0400 | Subject | Re: [PATCH 2/3] define ARM-specific dma_coherent_write_sync |
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On Oct 3, 2011, at 4:44 AM, Catalin Marinas wrote:
> On Mon, Oct 03, 2011 at 02:40:19AM +0100, Jon Masters wrote: >> On Sep 6, 2011, at 11:02 AM, Mark Salter wrote: >>> In any case, the current thinking is that the original problem with >>> the USB performance seen on cortex A9 multicore is probably something >>> more than just write buffer delays. Once the original problem is better >>> understood, we can take another look at this patch if it is still >>> needed. >> >> Thanks again for looking into this Mark. My understanding is that this >> is still being investigated. I'll followup with ARM to see how that's >> going since I've heard nothing recently :) Meanwhile, we're continuing >> to carry a hack based on these patches in Fedora ARM kernels. > > Not talking about hardware specifics here, the architecture (though > ARMv7 onwards) mandates that the write buffer is eventually drained. But > doesn't state any upper limit, so it could even be half a second.
<snip mechanics of dma_coherent_write_sync, etc.>
I guess my main question is, do you think this is just a write buffer delay? If you do, then we should definitely get back to this question of defining DMA extensions. But are we sure that's what this is?
Mark: did you have any more insight into this recently?
Jon.
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