linux-kernel - Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S driver

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Message-ID: <b5c581b9-17af-d004-33fb-2cc782ab820a@gmail.com>
Date:   Thu, 23 Jan 2020 18:16:01 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sameer Pujar <spujar@...dia.com>, Jon Hunter <jonathanh@...dia.com>
Cc:     perex@...ex.cz, tiwai@...e.com, robh+dt@...nel.org,
        devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        atalambedu@...dia.com, linux-kernel@...r.kernel.org,
        lgirdwood@...il.com, viswanathl@...dia.com, sharadg@...dia.com,
        broonie@...nel.org, thierry.reding@...il.com,
        linux-tegra@...r.kernel.org, rlokhande@...dia.com,
        mkumard@...dia.com, dramesh@...dia.com
Subject: Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S
 driver

23.01.2020 12:22, Sameer Pujar пишет:
> 
> 
> On 1/22/2020 9:57 PM, Dmitry Osipenko wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 22.01.2020 14:52, Jon Hunter пишет:
>>> On 22/01/2020 07:16, Sameer Pujar wrote:
>>>
>>> ...
>>>
>>>>>>>>>> +static int tegra210_i2s_remove(struct platform_device *pdev)
>>>>>>>>>> +{
>>>>>>>>>> +     pm_runtime_disable(&pdev->dev);
>>>>>>>>>> +     if (!pm_runtime_status_suspended(&pdev->dev))
>>>>>>>>>> +             tegra210_i2s_runtime_suspend(&pdev->dev);
>>>>>>>>> This breaks device's RPM refcounting if it was disabled in the
>>>>>>>>> active
>>>>>>>>> state. This code should be removed. At most you could warn
>>>>>>>>> about the
>>>>>>>>> unxpected RPM state here, but it shouldn't be necessary.
>>>>>>>> I guess this was added for safety and explicit suspend keeps clock
>>>>>>>> disabled.
>>>>>>>> Not sure if ref-counting of the device matters when runtime PM is
>>>>>>>> disabled and device is removed.
>>>>>>>> I see few drivers using this way.
>>>>>>> It should matter (if I'm not missing something) because RPM should
>>>>>>> be in
>>>>>>> a wrecked state once you'll try to re-load the driver's module.
>>>>>>> Likely
>>>>>>> that those few other drivers are wrong.
>>>>>>>
>>>>>>> [snip]
>>>>>> Once the driver is re-loaded and RPM is enabled, I don't think it
>>>>>> would use
>>>>>> the same 'dev' and the corresponding ref count. Doesn't it use the
>>>>>> new
>>>>>> counters?
>>>>>> If RPM is not working for some reason, most likely it would be the
>>>>>> case
>>>>>> for other
>>>>>> devices. What best driver can do is probably do a force suspend
>>>>>> during
>>>>>> removal if
>>>>>> already not done. I would prefer to keep, since multiple drivers
>>>>>> still
>>>>>> have it,
>>>>>> unless there is a real harm in doing so.
>>>>> I took a closer look and looks like the counter actually should be
>>>>> reset. Still I don't think that it's a good practice to make changes
>>>>> underneath of RPM, it may strike back.
>>>> If RPM is broken, it probably would have been caught during device
>>>> usage.
>>>> I will remove explicit suspend here if no any concerns from other
>>>> folks.
>>>> Thanks.
>>> I recall that this was the preferred way of doing this from the RPM
>>> folks. Tegra30 I2S driver does the same and Stephen had pointed me to
>>> this as a reference.
>>> I believe that this is meant to ensure that the
>>> device is always powered-off regardless of it RPM is enabled or not and
>>> what the current state is.
>> Yes, it was kinda actual for the case of unavailable RPM.
> 
>> Anyways, /I think/ variant like this should have been more preferred:
>>
>> if (!pm_runtime_enabled(&pdev->dev))
>>          tegra210_i2s_runtime_suspend(&pdev->dev);
>> else
>>          pm_runtime_disable(&pdev->dev);
> 
> I think it looks to be similar to what is there already.
> 
> pm_runtime_disable(&pdev->dev); // it would turn out to be a dummy call
> if !RPM
> if (!pm_runtime_status_suspended(&pdev->dev)) // it is true always if !RPM
>         tegra210_i2s_runtime_suspend(&pdev->dev);

Maybe this is fine for !RPM, but not really fine in a case of enabled
RPM. Device could be in resumed state after pm_runtime_disable() if it
wasn't suspended before the disabling.