linux-kernel - Re: [PATCH 2/2] ASoC: Codec: wm8962: declare ALC Coefficients as 4 separate registers

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Message-ID: <5615DEE2.6000906@mentor.com>
Date:	Thu, 8 Oct 2015 12:11:30 +0900
From:	Jiada Wang <jiada_wang@...tor.com>
To:	Mark Brown <broonie@...nel.org>
CC:	<lgirdwood@...il.com>, <perex@...ex.cz>, <tiwai@...e.com>,
	<patches@...nsource.wolfsonmicro.com>,
	<alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ASoC: Codec: wm8962: declare ALC Coefficients as
 4 separate registers

Hi


On 10/06/2015 08:01 PM, Mark Brown wrote:
> On Tue, Oct 06, 2015 at 04:06:55PM +0900, Jiada Wang wrote:
>
>> As ALC2 register is volatile, declare it as one of ALC Coefficients
>> register together with other non-volatile registers will cause issue,
>> in case wm8962 has enter suspend mode, and cache_only flag is set,
>> any attempt to read from ALC2 will fail.
>
>> Instead of declaring one ALC Coefficients register which contains
>> ALC1 ~ ALC3 and Noise Gate, this patch declares 4 separate registers,
>> so that regmap can handle these registers differently based on their
>> classification.
>
> I don't understand this commit log.  Why does regmap care how these
> registers are presented to userspace, and how does splitting the
> controls up address the problem with one of the registers being volatile?
> Surely that register still has the same problem?
>
.get callback function will call regmap_raw_read() to read register
value from these registers, when these 4 regsters are declared as one
"ALC coefficient" register, condition check of regmap_volatile_range()
will return false, thus regmap will go word by word for the cache from
each register of "ALC Coefficient", the failure scenario is, when
wm8962 is in suspend mode (cache_only flag is set), as ALC2 doesn't
have cached value, then any attempt to read from it fails,

By splitting these registers, regmap can handle ALC2 as a single
volatile register, and always read from HW

Thanks,
Jiada

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