linux-kernel - Re: [RFC PATCH v5 13/14] media: tegra-video: Add CSI MIPI pads calibration

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Message-ID: <5d2b67a1-9e85-606e-9bf2-802379d922f9@nvidia.com>
Date:   Wed, 29 Jul 2020 17:47:23 -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>,
        <sakari.ailus@....fi>, <robh+dt@...nel.org>,
        <helen.koike@...labora.com>
CC:     <sboyd@...nel.org>, <gregkh@...uxfoundation.org>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>
Subject: Re: [RFC PATCH v5 13/14] media: tegra-video: Add CSI MIPI pads
 calibration


On 7/29/20 5:27 PM, Sowjanya Komatineni wrote:
>
> On 7/29/20 4:59 PM, Sowjanya Komatineni wrote:
>>
>> On 7/29/20 4:25 PM, Dmitry Osipenko wrote:
>>> 28.07.2020 18:59, Sowjanya Komatineni пишет:
>>> ...
>>>>>> +        ret = tegra_mipi_finish_calibration(csi_chan->mipi);
>>>>>> +        if (ret < 0)
>>>>>> +            dev_err(csi_chan->csi->dev,
>>>>>> +                "MIPI calibration failed: %d\n", ret);
>>>>> Doesn't v4l2_subdev_call(OFF) need to be invoked here on error?
>>>> Not required as on error streaming fails and runtime PM will turn off
>>>> power anyway.
>>> I see that camera drivers bump theirs RPM on s_stream=1, and thus,
>>> s_stream=0 should be invoked in order to balance the RPM. What am I 
>>> missing?
>>>
>>> https://elixir.bootlin.com/linux/v5.8-rc4/source/drivers/media/i2c/ov2740.c#L634 
>>>
>>
>> Sensor drivers take care of RPM put when any failure happens during 
>> s_stream.
>>
>> So bridge driver don't have to call v4l2_subdev_call s_stream off 
>> incase if sensor subdev stream on fails.
>>
>>>> Also we only did csi subdev s_stream on and during sensor subdev
>>>> s_stream on fail, actual stream dont happen and on tegra side frame
>>>> capture by HW happens only when kthreads run.
>>> Secondly, perhaps a failed calibration isn't a very critical error?
>>> Hence just printing a warning message should be enough.
>>
>> Using dev_err to report calibration failure. Are you suggesting to 
>> use dev_warn instead of dev_err?
>>
OK I think I understood what you meant.

When v4l2_subdev_call for sensor s_stream ON fails, we dont have to do 
v4l2_subdev_call s_stream OFF.

As sensor drivers take care of RPM put when any failure happens during 
s_stream ON

Other case when v4l2_subdev_call for sensor s_stream ON is good, then 
tegra_mipi_finish_calibration fail need to call s_stream OFF for sensor.

Agree as calibration errors out in this case as its not critical in this 
scenario, So will change dev_err to dev_warn and will not report this as 
error so no need to call s_stream off.

>>>
>>> Could you please make a patch that factors all ON/OFF code paths into a
>>> separate functions? It's a bit difficult to follow the combined code,
>>> especially partial changes in the patches. Thanks in advance!
>>
>> what do you mean by partial changes in patches?
>>
>> Can you please be more clear?
>
> Also please specify what ON/OFF code paths you are referring to when 
> you say to move into separate functions?
>
>>
>> Thanks
>>
>> Sowjanya
>>