linux-kernel - Re: USB mass storage and ARM cache coherency

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Date:	Mon, 1 Feb 2010 23:30:01 +0100
From:	Andreas Mohr <andi@...as.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Ming Lei <tom.leiming@...il.com>, linux-usb@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	Greg KH <greg@...ah.com>, Takashi Iwai <tiwai@...e.de>
Subject: Re: USB mass storage and ARM cache coherency

[CC Takashi]

On Mon, Feb 01, 2010 at 05:29:14PM +0000, Catalin Marinas wrote:
> On Fri, 2010-01-29 at 18:54 +0000, Matthew Dharm wrote:
> > HOWEVER, I firmly believe that the cache-management functions belong with
> > the driver that actually talks to the low-level hardware, as that's the
> > only place where you can be 100% certain of what cache operations are
> > needed.  After all, I think someone is working on a USB-over-IP transport,
> > and trying to manage cache at the usb-storage level in that scenario is
> > just silly.
> > 
> > So, let's put this in the HCD drivers and be done with it.
> 
> The patch below is what fixes the I-D cache incoherency issues on ARM. I
> don't particularly like the solution but it seems to be the only one
> available.

Thanks very much for working on this amazingly large problem!

I took some time to add your patch to ehci-q.c / ohci-q.c
(for my *hci-ssb.c ASUS WL-500gP v2), on my now _heavily_ patched-up 2.6.31.9,
but _UNFORTUNATELY_ it kept locking up the same way as always when stopping
playback despite being damn sure this time that this patch could have
the potential to finally fix it ;)
(I had to replace memory.h with page.h on my arch though, to fix the build)

This is on MIPSEL (not one of my many ARM devices, unfortunately ;),
with usb-audio, and the madplay process crashes in __bzero(),
which strongly indicates cache coherency issues (other subsequent backtraces
have lots of mmap and vma listed, see also my "snd_usb_audio OOPS on MIPSEL -
is that the mmap issue?").

Next thing I'll do is fire up gdb and get a good backtrace of the
__bzero() address to find out which page handling in mpd exactly
is hampered with crashes. This is now ~ the third patch that I applied
on-the-go and that didn't help, so it's probably time to do
some earnest analysis on what's really going on locally.

Note that usb-storage itself does work on this platform though.

Rather annoying to be so close (sound works) yet so far away,
especially after all that USB host trouble I already had.

Thanks a lot again,

Andreas Mohr
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