Hi,
On Fri, Jun 20, 2014 at 09:14:34AM +0530, George Cherian wrote:
> On 6/20/2014 3:50 AM, Daniel Mack wrote:
> >Hi,
> >
> >I've been debugging issues with musb in host mode and both full-speed
> >and high-speed USB audio devices with cppi41 DMA mode enabled.
> >
> >The effect that was observed with full-speed devices was that CPU load
> >went up to 100% due to the dma channels dma_completion work struct.
> >For FS devices, the MUSB_TXCSR_TXPKTRDY bit that signals the FIFO's
> >emptyness takes a long time to be cleared, and if the worker function
> >determines that it's still set, it will re-queue the work immediately,
> >which effectively results in a busy poll that renders the system
> >unusable. There are audible crackles on the output, and every bit of
> >extra load will distort the audio stream even more.
> >
> >The work struct was introduced by 1af54b7a40 ("usb: musb: musb_cppi41:
> >Handle ISOCH differently and not use the hrtimer."), apparantly in
> >order to mitigate an "unreliable" behaviour of the driver.
> >
> >Geroge, do you recall which problems you saw, which device you tested
> >with and what the effect of this patch was for you? I'm asking because
> >I suspect the issue in fact lies in the hrtimer interval setup and can
> >hence be fixed well without the extra worker.
> >
> >Sebastian's patch to implement that timer (a655f481d: "usb: musb:
> >musb_cppi41: handle pre-mature TX complete interrupt") expressed some
> >uncertainty about the chosen value of 140us, and suspected that there's
> >a relation between the dma burst size and the minimum time value.
> >
> >Hence, I'm sending two patches. The first one reverts 1af54b7a40 as it
> >causes trouble with FS audio devices, and the seconds addresses the
> >issue by tweaking the hrtimer settings instead. This seems to work fine
> >with both FS and HS audio devices now.
> >
> >George, could you give this a try with your original test case?
>
> Yes, I would do by this weekend and update.
> Sorry that am lil busy with some trainings.
Do we have any new developments here ?
--
balbi
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