linux-kernel - Re: [PATCH] ASoC: fsl_ssi: remove explicit register defaults

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Date:	Mon, 01 Feb 2016 17:58:06 +0100
From:	"Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:	Fabio Estevam <festevam@...il.com>
CC:	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Timur Tabi <timur@...i.org>,
	Nicolin Chen <nicoleotsuka@...il.com>,
	Xiubo Li <Xiubo.Lee@...il.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: fsl_ssi: remove explicit register defaults

On 01.02.2016 13:25, Maciej S. Szmigiero wrote:
> On 01.02.2016 13:13, Fabio Estevam wrote:
>> Hi Maciej,
>>
>> On Mon, Feb 1, 2016 at 10:07 AM, Maciej S. Szmigiero
>> <mail@...iej.szmigiero.name> wrote:
>>> Is regmap patch from
>>> http://www.spinics.net/lists/kernel/msg2161934.html
>>> applied to the tested tree?
>>
>> Yes, linux-next 20160201 contains this patch.
> 
> Hmm, I will try to build this tree on UDOO board
> today and see what happens.

Looks like the problem occurs because commit
922a9f936e40 ("regmap: mmio: Convert to regmap_bus and fix accessor usage")
has removed ->read callback from MMIO regmap
implementation but it is used (via regmap_raw_read()) by
regcache code to initialize cache if reg default values
weren't provided explicitly.

If I revert this commit the SSI probes successfully again.

Looks like a possible solution would be to change
regmap_raw_read() to do read using _regmap_read in
case the cache is bypassed and there is no ->read
callback defined for regmap implementation.

Maciej