linux-kernel - Re: [alsa-devel] [PATCH] ASoC: Add support for multi register mux

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Message-ID: <20140331120748.GS2269@sirena.org.uk>
Date:	Mon, 31 Mar 2014 13:07:48 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Arun Shamanna Lakshmi <aruns@...dia.com>,
	Songhee Baek <sbaek@...dia.com>,
	"'alsa-devel@...a-project.org'" <alsa-devel@...a-project.org>,
	"'swarren@...dotorg.org'" <swarren@...dotorg.org>,
	"'tiwai@...e.de'" <tiwai@...e.de>,
	"'lgirdwood@...il.com'" <lgirdwood@...il.com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] [PATCH] ASoC: Add support for multi register mux

On Mon, Mar 31, 2014 at 01:55:52PM +0200, Lars-Peter Clausen wrote:
> On 03/31/2014 01:21 PM, Mark Brown wrote:

> >The above is a bit confusing...  partly this is because of a lack of
> >context (what is MULTI_MUX_INPUT_OFFSET?) and partly because it isn't
> >entirely obvious that stopping as soon as we see any value set is the
> >right choice, especially given the addition to rather than setting of
> >val.

> I think the idea is that since we know that for one-hot encodings only
> powers of two are valid values the other bits are used to encode the
> register number. E.g 0x4 means bit 3 in register 0, 0x5 means bit 3 in
> register 1, 0x6 means bit 3 in register 2 and so on. I guess it is possible
> to make it work. But this seems to be quite hack-ish to me. You'd have to be
> careful that MULTI_MUX_INPUT_OFFSET(reg_idx) never evaluates to a power of
> two and there are probably some more pitfalls.

Ugh, right.  The fact that I couldn't tell that this was what the code
was trying to do from looking at it is not a good sign here.

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