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

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Message-ID: <34ac1fd3-ae0f-07f2-555f-a55087a2c9dc@nvidia.com>
Date:   Wed, 22 Jan 2020 11:52:14 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Sameer Pujar <spujar@...dia.com>,
        Dmitry Osipenko <digetx@...il.com>, <perex@...ex.cz>,
        <tiwai@...e.com>, <robh+dt@...nel.org>
CC:     <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


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.

Now for Tegra210 (or actually 64-bit Tegra) RPM is always enabled and so
we don't need to worry about the !RPM case. However, I still don't see
the harm in this.

Jon

-- 
nvpublic