linux-kernel - Re: [PATCH] ASoC: wm_hubs: Fix DC Servo readback

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Date:	Wed, 13 Aug 2014 13:40:46 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
Cc:	Nikesh Oswal <nikesh@...nsource.wolfsonmicro.com>,
	lgirdwood@...il.com, tiwai@...e.de, alsa-devel@...a-project.org,
	patches@...nsource.wolfsonmicro.com, linux-kernel@...r.kernel.org,
	perex@...ex.cz
Subject: Re: [PATCH] ASoC: wm_hubs: Fix DC Servo readback

On Wed, Aug 13, 2014 at 01:16:37PM +0100, Charles Keepax wrote:
> On Wed, Aug 13, 2014 at 12:38:41PM +0100, Mark Brown wrote:
> > On Wed, Aug 13, 2014 at 12:08:44PM +0100, Charles Keepax wrote:

> > > Also I think the situation is more complex for example on version
> > > 4.4 of the datasheet for wm8994 the WR_VAL fields appear to be in
> > > register 59h. Which is not consistent with this.

> > There was a change in the DC servo between revisions of the WM8994 (at
> > revision E from the look of the code).  This isn't documented in the
> > datasheets as they only document current silicon.

> Indeed, but this patch sets all revs of wm8994 to use register 57h.
> The lastest version of the datasheet has this register at 59h
> although some of the older versions of the datasheet (which likely
> match some older revs of the chip although no way to tell which one
> just from the datasheet) have it at 57h.

Yes, I'm agreeing with you - I'm pointing out what Nikesh has missed
(you can see this from the changelogs as well).  The patch will break
anything using older devices.

> I think basically we need to get some clarity from hardware here
> on which revs use which address and update this patch to match,
> but either way it looks likely that this patch doesn't address
> the whole picture.

This code got rather a lot of attention...

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