linux-kernel - Re: [PATCH AUTOSEL 5.7 055/388] ASoC: SOF: Do nothing when DSP PM callbacks are not set

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Date:   Thu, 18 Jun 2020 08:56:22 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Daniel Baluta <daniel.baluta@....com>,
        Mark Brown <broonie@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        sound-open-firmware@...a-project.org, alsa-devel@...a-project.org
Subject: Re: [PATCH AUTOSEL 5.7 055/388] ASoC: SOF: Do nothing when DSP PM
 callbacks are not set



On 6/18/20 6:44 AM, Daniel Baluta wrote:
> On 6/18/20 2:01 PM, Mark Brown wrote:
>> On Wed, Jun 17, 2020 at 09:02:32PM -0400, Sasha Levin wrote:
>>> From: Daniel Baluta <daniel.baluta@....com>
>>>
>>> [ Upstream commit c26fde3b15ed41f5f452f1da727795f787833287 ]
>>>
>>> This provides a better separation between runtime and PM sleep
>>> callbacks.
>>>
>>> Only do nothing if given runtime flag is set and calback is not set.
>>>
>>> With the current implementation, if PM sleep callback is set but runtime
>>> callback is not set then at runtime resume we reload the firmware even
>>> if we do not support runtime resume callback.
>> This doesn't look like a bugfix, just an optimization?
> 
> Indeed can be seen as an optimization, but it does unexpected things 
> which can cause trouble
> 
> and weird behavior for people not familiar with the matter.
> 
> For example, as explained in the commit message if you only provide
> 
> System PM handler but not runtime PM handler, then the DSP will be resetted
> 
> even if this is not the intention.

I think it's a bug fix for Intel legacy platforms (Baytrail, Broadwell) 
where runtime_pm isn't supported. However the additional fixes for 
system suspend/resume were only provided for 5.8, so this patch in 
isolation will not do much for those platforms. Put differently, even if 
this patch is applied to 5.7 suspend/resume would still not work for 
Baytrail/Broadwell.
Daniel, your call if you need this for i.MX?