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 08:08:29 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


On 4/28/20 7:59 AM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 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.

Before channel stream we enable power/clocks and after streaming we stop.

So without refcount, on stream stop of any of the channel RPM put turns 
power/clock but other channels will still be streaming.