On Wed, Jun 18, 2014 at 11:28:25AM +0200, Daniel Mack wrote:
> Hi,
Hi Daniel,
>
> 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?
>
> Note that these patches are to be applied on top of my musb/cppi41
> cleanup series that I sent ~3 weeks ago.
Could you test, whether this commit also fixes your problem ?
https://lkml.org/lkml/2014/6/20/598
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