linux-kernel - Re: [PATCH v1] ALSA: hda: cs35l41: Stop creating ALSA Controls for firmware coefficients

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Message-ID: <551e3be0-f436-4db1-ae5c-1ad5a31f68c3@perex.cz>
Date: Wed, 31 Jul 2024 12:36:19 +0200
From: Jaroslav Kysela <perex@...ex.cz>
To: Takashi Iwai <tiwai@...e.de>
Cc: Stefan Binding <sbinding@...nsource.cirrus.com>,
 Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
 linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org,
 patches@...nsource.cirrus.com
Subject: Re: [PATCH v1] ALSA: hda: cs35l41: Stop creating ALSA Controls for
 firmware coefficients

On 31. 07. 24 12:30, Takashi Iwai wrote:
> On Tue, 30 Jul 2024 16:55:19 +0200,
> Jaroslav Kysela wrote:
>>
>> On 30. 07. 24 16:37, Stefan Binding wrote:
>>> Add a kernel parameter to allow coefficients to be exposed as ALSA controls.
>>>
>>> When the CS35L41 loads its firmware, it has a number of controls to
>>> affect its behaviour. Currently, these controls are exposed as ALSA
>>> Controls by default.
>>>
>>> However, nothing in userspace currently uses them, and is unlikely to
>>> do so in the future, therefore we don't need to create ASLA controls
>>> for them.
>>>
>>> These controls can be useful for debug, so we can add a kernel
>>> parameter to re-enable them if necessary.
>>>
>>> Disabling these controls would prevent userspace from trying to read
>>> these controls when the CS35L41 is hibernating, which ordinarily
>>> would result in an error message.
>>
>> This is probably not a right argument to add this code. The codec
>> should be powered up when those controls are accessed or those
>> controls should be cached by the driver.
>>
>> Although the controls have not been used yet, exposing them in this
>> way is not ideal.
>>
>> Could you fix the driver (no I/O errors)?
> 
> While we should fix the potential errors at hibernation, it's not bad
> to hide those controls, IMO.  For the normal use cases, it's nothing
> but a cause of troubles, after all.

I do not think that the situation is so obvious. Different coefficients can be 
used in various UCM profiles for example.

But for debugging we have debugfs when the developer thinks that the feature 
is not useful for users. The module parameter solution is not good in my eyes.

					Jaroslav

-- 
Jaroslav Kysela <perex@...ex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.