linux-kernel - Re: [RFC PATCH v1 3/5] media: tegra-video: Move PM runtime handle to streaming

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Date:   Tue, 28 Apr 2020 17:59:13 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, frankc@...dia.com,
        hverkuil@...all.nl
Cc:     linux-media@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 3/5] media: tegra-video: Move PM runtime handle to
 streaming

28.04.2020 17:51, Sowjanya Komatineni пишет:
> 
> On 4/28/20 6:59 AM, Dmitry Osipenko wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 28.04.2020 07:20, Sowjanya Komatineni пишет:
>>> diff --git a/drivers/staging/media/tegra-video/csi.c
>>> b/drivers/staging/media/tegra-video/csi.c
>>> index b3dd0c3..29ccdae 100644
>>> --- a/drivers/staging/media/tegra-video/csi.c
>>> +++ b/drivers/staging/media/tegra-video/csi.c
>>> @@ -272,8 +272,25 @@ static int tegra_csi_s_stream(struct v4l2_subdev
>>> *subdev, int enable)
>>>        struct tegra_vi_channel *chan = v4l2_get_subdev_hostdata(subdev);
>>>        struct tegra_csi_channel *csi_chan = to_csi_chan(subdev);
>>>        struct tegra_csi *csi = csi_chan->csi;
>>> +     int ret;
>>> +
>>> +     if (enable && atomic_add_return(1, &csi->clk_refcnt) == 1) {
>>> +             ret = pm_runtime_get_sync(csi->dev);
>>> +             if (ret < 0) {
>>> +                     dev_err(csi->dev,
>>> +                             "failed to get runtime PM: %d\n", ret);
>>> +                     pm_runtime_put_noidle(csi->dev);
>>> +                     atomic_dec(&csi->clk_refcnt);
>>> +                     return ret;
>>> +             }
>>> +     }
>>> +
>>> +     ret = csi->ops->csi_streaming(csi_chan, chan->pg_mode, enable);
>>>
>>> -     return csi->ops->csi_streaming(csi_chan, chan->pg_mode, enable);
>>> +     if ((ret < 0 || !enable) && atomic_dec_and_test(&csi->clk_refcnt))
>>> +             pm_runtime_put_sync(csi->dev);
>> Runtime PM maintains its own refcount, why these
>> clk_refcnt/power_on_refcnt are needed?
> 
> Streaming is per channel and we can't turn power/clocks off while other
> channels may still be running.
> 

All channels use the same CSI device. You should remove the custom
refcounting.

BTW, next time you'll really need to do refcounting, use the generic kref.