linux-kernel - Re: Allocating buffers for USB transfers (again)

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Message-ID: <20110812044605.GA8533@xanatos>
Date:	Thu, 11 Aug 2011 21:46:05 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Daniel Mack <zonque@...il.com>
Cc:	Matěj Laitl <matej@...tl.cz>,
	Alan Stern <stern@...land.harvard.edu>,
	Florian Mickler <florian@...kler.org>,
	Oliver Neukum <oliver@...kum.org>, linux-usb@...r.kernel.org,
	alsa-devel@...a-project.org, Takashi Iwai <tiwai@...e.de>,
	Clemens Ladisch <clemens@...isch.de>, pedrib@...il.com,
	William Light <wrl@...est.net>, Greg KH <greg@...ah.com>,
	linux-kernel@...r.kernel.org, Robert Hancock <hancockrwd@...il.com>
Subject: Re: Allocating buffers for USB transfers (again)

On Fri, Aug 12, 2011 at 03:28:42AM +0200, Daniel Mack wrote:
> On Fri, Aug 12, 2011 at 1:50 AM, Matěj Laitl <matej@...tl.cz> wrote:
> > On 12. 8. 2011 Daniel Mack wrote:
> >> > This patch actually makes the sound playback _worse_. Now I get strange
> >> > squawks where previously at least first seconds of a song sounded
> >> > normally.
> >> >
> >> > However, I no longer get "zero length buffer submitted" or that "...
> >> > Weird." debug messages, only several megabytes of: (should I post these
> >> > somewhere?)
> >> >
> >> > xhci_hcd 0000:05:00.0: Giveback URB ffff880114cec000, len = 880,
> >> > expected = 1000, status = -115
> >> > xhci_hcd 0000:05:00.0: Giveback URB ffff880114740000, len = 352,
> >> > expected = 1000, status = -115
> >> > xhci_hcd 0000:05:00.0: underrun event on endpoint
> >>
> >> Might be the hardware doesn't like this. As I said, the patch is blindly
> >> written and I couldn't test it. Did you test this on a EHCI port as well?
> >
> > Good point, this patch distorts the playback also on the EHCI port. (the
> > playback seems to be 10 times slower than it should be)
> 
> And it is only this *last* patch that causes it, yes?
> 
> If that is the case, we need empty subframes in the middle of urbs,
> and we need to figure a way how to teach the XHCI driver to cope with
> that, too.

By empty subframes, you mean zero-length frame buffers in the middle of
the URB, correct?  Andiry and Alan had some suggestions for how to fix
that, so I'll try to cook up a patch tomorrow.  Then we'll have to
"unpeel" the debug patches and make sure the system is still usable.

Sarah Sharp
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