AACI broken with commit 29a4f2d3

[Philby John]

On Thu, 2010-03-25 at 12:16 +0000, Russell King - ARM Linux wrote:
> On Thu, Mar 25, 2010 at 12:02:37PM +0000, Catalin Marinas wrote:
> > I can confirm that it solves the reset issue on other RealView boards as
> > well. Whether it's the correct fix I can't tell.
> 
> Something else is going on then.  Whatever, this patch is totally
> incorrect and needs to be reverted.  It's not even doing what the
> description in the documentation requires.
> 
> I quote from page 3-18, which is mentioned in the commit message which
> added this code:
> 
>   Data transmitted on slot 2 register, AACISL2TX The AACISL2TX register
>   is a read/write register. When a write occurs to this register the data
>   it contains is sent on the next available frame in slot 2. If a power
>   down is required, then data must be written to AACISL1TX location
>   address 0x26, which is recorded by the PrimeCell AACI. If the AACISL2TX
>   bit 16 is set, then the PrimeCell AACI goes into power down mode.
>   Table 3-11 shows the bit assignment of the AACISL2TX register.
> 
> And this is definitely NOT what Philby's code is doing.
> 
> The original commit is wrong on soo many levels.

Here is the background work I did previously for the original patch.

Dumped entire AACI registers when reading used to fail. The difference between
a working and non-working probe is confined to just 4 registers.

Working                         Non-Working

0007C000: SL1RX                 00000000: SL1RX
0004E530: SL2RX                 00000000: SL2RX
00000A80: slot flags            00000A02: slot flags
00000000: main flag register    00000002: main flag register

Of which what's interesting are the "slot flags" and the "main flag register".
The slot flag register (AACISLFR) has its 1st bit set to 1, meaning Slot 1
transceiver is busy, when reading vendor/product id (times out after 10 tries).

The manual mandates powering down of the aaci module to attain reset values
(page 3-18, 2-7) by setting AACIRESET. But ofcourse to attain default state its useless
putting them in any clean up routine. That's why I introduced them at probe time. Here is
another way to solve the problem.

>From c10d6111657d881bea53d8559deb7422d0f46583 Mon Sep 17 00:00:00 2001
From: Philby John <pjohn at in.mvista.com>
Date: Fri, 26 Mar 2010 16:41:06 +0530
Subject: [PATCH] Fix alignment faults on ARM Cortex introduced by commit 29a4f2d3

The commit 29a4f2d3 uses writel() on the AC97_POWERDOWN register
which is half-word aligned causing unaligned exceptions on a
Cortex-A8. The original patch solved the "aaci-pl041 fpga:04:
ac97 read back fail" issue on a soft reset. Reading from 0x26
also clears AACISL1TX/AACISL2TX slots for transmit.

Signed-off-by: Philby John <pjohn at mvista.com>
---
 sound/arm/aaci.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/sound/arm/aaci.c b/sound/arm/aaci.c
index 656e474..6d677c2 100644
--- a/sound/arm/aaci.c
+++ b/sound/arm/aaci.c
@@ -863,7 +863,11 @@ static int __devinit aaci_probe_ac97(struct aaci *aaci)
 	struct snd_ac97 *ac97;
 	int ret;
 
-	writel(0, aaci->base + AC97_POWERDOWN);
+	/*
+	 * Fix: ac97 read back fail errors by reading
+	 * from Power down register
+	 */
+	readw(aaci->base + 0x26);
 	/*
 	 * Assert AACIRESET for 2us
 	 */
-- 
1.7.0.1