linux-kernel - Re: [PATCH] ASoC: sgtl5000: only check VDDD-supply, not revision

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Message-ID: <575264A4.2070709@nelint.com>
Date:	Sat, 4 Jun 2016 07:18:28 +0200
From:	Eric Nelson <eric@...int.com>
To:	Fabio Estevam <festevam@...il.com>,
	Clemens Gruber <clemens.gruber@...ruber.com>
Cc:	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Mark Brown <broonie@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: sgtl5000: only check VDDD-supply, not revision

Hi Fabio and Clemens,

On 06/03/2016 06:23 PM, Eric Nelson wrote:
> Hi Fabio,
> 
> On 06/02/2016 05:48 PM, Fabio Estevam wrote:
>> Hi Clemens,
>>
>> On Thu, Jun 2, 2016 at 9:47 AM, Clemens Gruber
>> <clemens.gruber@...ruber.com> wrote:
>>> Instead of checking the SGTL5000 chip revision, we should only check if
>>> the VDDD regulator exists and only call sgtl5000_replace_vddd_with_ldo
>>> if the regulator is missing.
>>> Otherwise, the user reads in the kernel log that the internal LDO is
>>> used, even though he did follow the NXP recommendation to use external
>>> VDDD and also specified VDDD-supply in the devicetree.
>>>
>>> Also remove the comment, which incorrectly states that external VDDD is
>>> only supported for SGTL5000 chip revisions < 0x11.
>>> Official NXP documentation recommends using external VDDD and not the
>>> internal LDO due to the SGTL5000 erratum ER1. This also applies to
>>> revisions >= 0x11.
>>>
>>> Tested on an i.MX6Q board with SGTL5000 rev 0x11 and external VDDD.
>>
>> Patch looks good to me.
>>
>> Eric,
>>
>> Sometime ago you were looking at this. What do you think about this patch?
>>
> 
> Sorry. I'm traveling and haven't had a chance to review this, but it's
> on my to-do.
> 
> 

AFAIK, the SGTL5000 versions < 0x11 are like Sasquatch: I've seen
no real proof of their existence. I tried to chase down when this
code was introduced, but it seems to have been around since
the dawn of the driver.

Clemens, if you're really trying to control an external regulator,
I think you'll need lots more than this patch. There are some
fundamental flaws in regulator handling and I put together some
RFC patches to address them in February 2015:
	http://mailman.alsa-project.org/pipermail/alsa-devel/2015-February/thread.html#88353

The long and short of it is that at least one of the regulators
would need to be initialized before the SGTL5000 probes.

Regards,


Eric