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

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Message-ID: <20140320183638.GI11706@sirena.org.uk>
Date:	Thu, 20 Mar 2014 18:36:38 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Arun Shamanna Lakshmi <aruns@...dia.com>,
	"lgirdwood@...il.com" <lgirdwood@...il.com>,
	"perex@...ex.cz" <perex@...ex.cz>, "tiwai@...e.de" <tiwai@...e.de>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Songhee Baek <sbaek@...dia.com>
Subject: Re: [PATCH] ASoC: Add support for multi register mux

On Thu, Mar 20, 2014 at 12:20:17PM -0600, Stephen Warren wrote:
> On 03/20/2014 05:48 AM, Mark Brown wrote:
> > On Wed, Mar 19, 2014 at 04:44:00PM -0700, Arun Shamanna Lakshmi wrote:

> >> If each bit of a 32 bit register maps to an input of a mux, then with
> >> the current 'soc_enum' structure we cannot have more than 64 inputs
> >> for the mux (because of reg and reg2 only).

> > What makes you say that?  We currently have devices in mainline which
> > have well over 32 inputs to muxes.

> I think their register layout is different.

> I found a number of large muxes where the register stores a 'integer'
> indicating which mux input to select, e.g. Arizona, WM2200, etc. In this
> case, an N-bit register could support up to 2^N inputs.

> However, the registers in the Tegra AHUB use 1 bit position per input,
> and require you to set one single bit at a time. Hence, an N bit
> register (or string of registers) can support up to N inputs. In more
> recent Tegra chips, we have at least >32 inputs and I think Arun was
> saying even >64 inputs. That requires 2 or 3 or more .reg fields in
> struct soc_enum.

Right, that was my guess too (the mail wasn't terribly clear with the
formatting, references to unpublished documents and so on) but that's
not a straight mux, it's a value mux, and the limit with the current
code is much lower on 32 bit systems (like at least some of the K1s)
since muxes only use one of the current register fields.

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