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

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Date:   Wed, 22 Jan 2020 09:23:29 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sameer Pujar <spujar@...dia.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, jonathanh@...dia.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

22.01.2020 07:32, Sameer Pujar пишет:
[snip]
>>>>> +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.

>>>>> +     int rx_fifo_th;
>>>> Could rx_fifo_th be negative?
>>> rx_fifo_th itself does not take negative values, explicit
>>> typecasting> is avoided in "if" condition by declaring this as "int"
>> Explicit typecasting isn't needed for integers.
> 
> What I meant was, rx_fifo_th is checked against a 'int' variable in an
> "if" condition.

What's the problem with comparing of unsigned with signed?

Besides, cif_conf.audio_ch > I2S_RX_FIFO_DEPTH can't be ever true, isn't
it? I2S_RX_FIFO_DEPTH=64, channels_max=16

Lastly, nothing stops you to make max_th unsigned.