Re: [PATCH 2/2] usb: musb: Size 1 dma in transfers won't complete with cpp41

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On Thu, Jan 19, 2017 at 07:04:57AM -0800, Tony Lindgren wrote:
> * Bin Liu <b-liu@xxxxxx> [170118 19:42]:
> > On Wed, Jan 18, 2017 at 06:29:59PM -0800, Tony Lindgren wrote:
> > > At least with the cppi41 dma, size 1 in dma transfers will just wait
> > 
> > In which case do you see the size 1 transfer? using testusb?
> > 
> > > until the device is disconnected. This causes timeouts in cppi41 dma
> > > runtime PM.
> > > 
> > > Also the initial size 8 transfers take about 200ms to complete when
> > > plugging a USB mass storage device to a hub. But we probably want to
> > > keep those to avoid using PIO.
> > > 
> > > Fix the issue by adding a quirk for cppi41 and skip size 1 in dma if
> > > set.
> > 
> > It is fine to bypass dma for size 1 transfers, due to the dma setup
> > overhead. But I'd like to know the test case to understand why it hangs.
> 
> The test case is the same old connect a USB mass storage device to a hub.
> There we see the initial size 1 transfer in the beginning. That transfer
> seems to never complete with cppi41 and the transfer will stay active
> until the device is disconnected. Currently we don't seem to have any
> timeout mechanism in cppi41 for that.

Ok, I will take a look maybe sometime next week to understand the
traffic.

BTY, it seems you missed my comment at the end which is about limiting
the transfer size.

Regards,
-Bin.
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