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

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Message-ID: <9f73afdf-1e9a-cdbd-f972-a022d503ef51@nvidia.com>
Date:   Fri, 24 Jan 2020 09:07:22 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Sameer Pujar <spujar@...dia.com>
CC:     <devicetree@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <lgirdwood@...il.com>, <linux-kernel@...r.kernel.org>,
        <broonie@...nel.org>, <atalambedu@...dia.com>, <tiwai@...e.com>,
        <viswanathl@...dia.com>, <linux-tegra@...r.kernel.org>,
        <robh+dt@...nel.org>, <thierry.reding@...il.com>,
        <sharadg@...dia.com>, <rlokhande@...dia.com>, <mkumard@...dia.com>,
        <dramesh@...dia.com>
Subject: Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S
 driver


On 23/01/2020 15:16, Dmitry Osipenko wrote:
> 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.

I don't see any problem with this for the !RPM case.

Jon

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