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

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Date:   Wed, 22 Jan 2020 19:26:19 +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 10:16, Sameer Pujar пишет:
> 
> 
> On 1/22/2020 11:53 AM, Dmitry Osipenko wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 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.
> 
> 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.
>>
>>>>>>> +     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?
> 
> consider this example,
> ----
> unsigned int x = 5;
> int y = -1;
> 
> (x > y) is false.

Right

> ----
> Hence should be careful while using signed and unsigned comparisons.
>>
>> 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
> 
> Yes true.
>> Lastly, nothing stops you to make max_th unsigned.
> 
> will update.
> 

Thanks