linux-kernel - Re: [PATCH 2/2] USB: ehci-tegra: fix inefficient copy of unaligned buffers

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Message-ID: <20150407195932.GB12027@localhost>
Date:	Tue, 7 Apr 2015 21:59:32 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Johan Hovold <johan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-tegra@...r.kernel.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH 2/2] USB: ehci-tegra: fix inefficient copy of unaligned
 buffers

On Tue, Apr 07, 2015 at 11:30:15AM -0400, Alan Stern wrote:
> On Tue, 7 Apr 2015, Johan Hovold wrote:
> 
> > Make sure only to copy any actual data rather than the whole buffer,
> > when releasing the temporary buffer used for unaligned transfer buffers.
> > 
> > Note that the corresponding fix of musb also fixes a lockup on
> > disconnect, where repeated failed transfers would starve the hub
> > workqueue from processing the disconnect, which would have prevented the
> > urbs from being resubmitted. In this case there is no data to forward,
> > but the full buffer length was being copied nonetheless.
> 
> This is wrong for isochronous transfers, because the transfer data
> generally isn't contiguous in memory.
> 
> It would be okay to do this for other transfer types, though.

Thanks for pointing that out. I'll re-spin the series tomorrow.

Johan
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