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

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Message-ID: <264d3354-8a2e-ee12-44ae-aff69213d551@nvidia.com>
Date:   Fri, 24 Jan 2020 09:51:23 +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 24/01/2020 09:07, Jon Hunter wrote:
> 
> 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.

Sorry I meant the RPM case. In other words, I don't see a problem for
neither the RPM case of the !RPM case.

Jon

-- 
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