linux-kernel - Re: [PATCH 9/9] ASoC: cs35l41: Use devm_pm_runtime

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Message-ID: <de9bf872-16ca-4b4e-9543-87f463b985a0@collabora.com>
Date:   Wed, 6 Sep 2023 22:55:28 +0300
From:   Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>
Cc:     James Schulman <james.schulman@...rus.com>,
        David Rhodes <david.rhodes@...rus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Stefan Binding <sbinding@...nsource.cirrus.com>,
        alsa-devel@...a-project.org, patches@...nsource.cirrus.com,
        linux-kernel@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH 9/9] ASoC: cs35l41: Use devm_pm_runtime_enable()

On 9/6/23 19:37, Charles Keepax wrote:
> On Tue, Sep 05, 2023 at 10:15:46PM +0300, Cristian Ciocaltea wrote:
>> On 9/5/23 12:45, Charles Keepax wrote:
>>> On Sun, Sep 03, 2023 at 12:06:21AM +0300, Cristian Ciocaltea wrote:
>>>> Simplify runtime PM during probe by converting pm_runtime_enable() to
>>>> the managed version.
>>>>
>>>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
>>>> ---
>>>> @@ -1376,7 +1379,6 @@ void cs35l41_remove(struct cs35l41_private *cs35l41)
>>>>  	cancel_work_sync(&cs35l41->mdsync_up_work);
>>>>  
>>>>  	pm_runtime_get_sync(cs35l41->dev);
>>>> -	pm_runtime_disable(cs35l41->dev);
>>>>  
>>>>  	regmap_write(cs35l41->regmap, CS35L41_IRQ1_MASK1, 0xFFFFFFFF);
>>>>  	if (cs35l41->hw_cfg.bst_type == CS35L41_SHD_BOOST_PASS ||
>>>
>>> Are we sure this is safe? The remove handler appears to be
>>> written to disable pm_runtime at the start presumably to stop the
>>> resume/suspend handler running during the remove callback.
>>> Whereas after this change the pm_runtime isn't disabled until
>>> after the remove callback has run. Does this open a window were
>>> we could get an erroneous pm_runtime suspend after the
>>> pm_runtime_put_noidle?
>>
>> I've just made a test adding a 6s sleep before returning from the remove 
>> handler: 
>>
>> [14444.894316] cs35l41 spi-VLV1776:00: Runtime resume
>> [14444.894469] cs35l41 spi-VLV1776:00: sleep 6s before return of cs35l41_remove()
>> [14448.338994] cs35l41 spi-VLV1776:00: Runtime suspend
>> [14451.079649] cs35l41 spi-VLV1776:00: return from cs35l41_remove()
>> [14451.080129] cs35l41 spi-VLV1776:00: Runtime resume
>> [14451.080165] cs35l41 spi-VLV1776:00: ASoC: Unregistered DAI 'cs35l41-pcm'
>> [14451.080181] cs35l41 spi-VLV1776:00: Runtime suspend
>> [14451.813639] acp5x_i2s_playcap acp5x_i2s_playcap.0: ASoC: Unregistered DAI 'acp5x_i2s_playcap.0'
>>
>> As expected, suspend triggered, but a resume was issued later, before DAI
>> got unregistered.
>>
>> I didn't notice any issues while repeating the test several times, hence 
>> I wonder what would be the reason to prevent getting suspend/resume events 
>> at this point?
> 
> The enter/exit hibernate code might run, which at the very
> least might result in a bunch of unexpected and failing bus
> traffic. Having a bit of a poke through the code, I guess the
> most dangerous thing would if you actually got as far as an
> extra runtime resume. This might cause cs35l41_init_boost
> to run which would undo the work done by the call to
> cs35l41_safe_reset in remove, which could leave the boost in a
> dangerous state when we enable reset/power down the supplies,
> which I think was not considered good. But its just likely
> simpler/cleaner if we don't have to think about all the
> possible implications of such things by just not allowing
> it to happen.

Agree, let's keep it simple. I will revert the change and instead ensure
a proper cleanup of pm_runtime_use_autosuspend(), according to the
documentation:

"It's important to undo this with pm_runtime_dont_use_autosuspend() at
driver exit time unless your driver initially enabled pm_runtime with
devm_pm_runtime_enable() (which handles it for you)."

Thanks for the clarifications,
Cristian