From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Mon, 7 Feb 2011 15:13:13 +0000
Subject: [PATCH -next] ALSA: AACI: fix crash in aaci_size_fifo
In-Reply-To: <1297091227-27142-1-git-send-email-marc.zyngier@arm.com>
References: <1297091227-27142-1-git-send-email-marc.zyngier@arm.com>
Message-ID: <20110207151313.GA5853@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Feb 07, 2011 at 03:07:07PM +0000, Marc Zyngier wrote:
> Commit ad58498 (ALSA: AACI: allow writes to MAINCR to take effect)
> that appeared in next-20110207 added a statement treating the maincr
> value as an address.  This leads to a crash while probing the device:
> 
> Unable to handle kernel NULL pointer dereference at virtual address 00000079
> pgd = c0004000
> [00000079] *pgd=00000000
> Internal error: Oops: 1 [#1] PREEMPT SMP
> last sysfs file:
> Modules linked in:
> CPU: 2    Not tainted  (2.6.38-rc3-next-20110207-00031-g7ed0487 #12)
> PC is at aaci_probe+0x438/0x5bc
> LR is at 0x79
> pc : [<c0385b98>]    lr : [<00000079>]    psr: 60000013
> sp : df83beb0  ip : e08be000  fp : 00000000
> r10: 00000000  r9 : 00000000  r8 : 00000000
> r7 : c048e1c0  r6 : df9a65f8  r5 : c0492840  r4 : 00000200
> r3 : 00000000  r2 : e08be000  r1 : 00000079  r0 : 00000078
> Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
> Control: 10c5387f  Table: 8000406a  DAC: 00000015
> 
> As this is probably only a debug leftover, get rid of the statement altogether.

No.  Reading back from the register makes sure that the write hits the device
before we delay.