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

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Message-ID: <3f51939d-cf4b-f69b-728a-7eb99bbae458@nvidia.com>
Date:   Wed, 22 Jan 2020 12:46:07 +0530
From:   Sameer Pujar <spujar@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, <perex@...ex.cz>,
        <tiwai@...e.com>, <robh+dt@...nel.org>
CC:     <spujar@...dia.com>, <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



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.
----
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.