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

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Date:	Thu, 20 Mar 2014 12:20:17 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mark Brown <broonie@...nel.org>,
	Arun Shamanna Lakshmi <aruns@...dia.com>
CC:	"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>,
	Stephen Warren <swarren@...dotorg.org>
Subject: Re: [PATCH] ASoC: Add support for multi register mux

On 03/20/2014 05:48 AM, Mark Brown wrote:
> On Wed, Mar 19, 2014 at 04:44:00PM -0700, Arun Shamanna Lakshmi wrote:
> 
> Don't top post and fix your mailer to word wrap within paragraphs, your
> mail is very hard to read.
> 
>> 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.
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