linux-kernel - Re: [RFC PATCH v6 09/10] media: tegra-video: Add CSI MIPI pads calibration

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Date:   Fri, 31 Jul 2020 14:03:23 -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>
Subject: Re: [RFC PATCH v6 09/10] media: tegra-video: Add CSI MIPI pads
 calibration


On 7/31/20 1:42 PM, Dmitry Osipenko wrote:
> 31.07.2020 19:29, Sowjanya Komatineni пишет:
>> On 7/31/20 9:14 AM, Dmitry Osipenko wrote:
>>> 31.07.2020 18:46, Sowjanya Komatineni пишет:
>>>> On 7/31/20 4:39 AM, Dmitry Osipenko wrote:
>>>>> 31.07.2020 12:02, Sowjanya Komatineni пишет:
>>>>> ...
>>>>>> @@ -249,13 +249,47 @@ static int tegra_csi_enable_stream(struct
>>>>>> v4l2_subdev *subdev)
>>>>>>             return ret;
>>>>>>         }
>>>>>>     +    if (csi_chan->mipi) {
>>>>>> +        ret = tegra_mipi_enable(csi_chan->mipi);
>>>>>> +        if (ret < 0) {
>>>>>> +            dev_err(csi->dev,
>>>>>> +                "failed to enable MIPI pads: %d\n", ret);
>>>>>> +            goto rpm_put;
>>>>>> +        }
>>>>>> +
>>>>>> +        /*
>>>>>> +         * CSI MIPI pads PULLUP, PULLDN and TERM impedances need to
>>>>>> +         * be calibrated after power on.
>>>>>> +         * So, trigger the calibration start here and results will
>>>>>> +         * be latched and applied to the pads when link is in LP11
>>>>>> +         * state during start of sensor streaming.
>>>>>> +         */
>>>>>> +        ret = tegra_mipi_start_calibration(csi_chan->mipi);
>>>>>> +        if (ret < 0) {
>>>>>> +            dev_err(csi->dev,
>>>>>> +                "failed to start MIPI calibration: %d\n", ret);
>>>>>> +            goto disable_mipi;
>>>>>> +        }
>>>>> What would happen if CSI stream is enabled and then immediately
>>>>> disabled
>>>>> without enabling camera sensor?
>>>> Nothing will happen as during stream enable csi receiver is kept ready.
>>>>
>>>> But actual capture will not happen during that point.
>>> Could you please show how the full call chain looks like? It's not clear
>>> to me what keeps CSI stream "ready".
>> VI is the main video input (video device) and on streaming it starts
>> stream of CSI subdev prior to stream of Sensor.
>>
>> HW path, sensor stream (CSI TX) -> CSI stream (RX)
>>
>> During CSI stream on, CSI PHY receiver is enabled to start receiving the
>> data but internally capture assembled to active state will happen only
>> when Tegra VI single shot is issues where VI thru pixel parser gets
>> captures data into the memory
> Alright, I see now.
>
> Will be great if you could change this hunk:
>
> {
>    ret = v4l2_subdev_call(src_subdev, video, s_stream, true);
>    if (ret < 0 && ret != -ENOIOCTLCMD) {
>      tegra_mipi_cancel_calibration(csi_chan->mipi);
>      v4l2_subdev_call(csi_subdev, video, s_stream, false);
>      return ret;
>    }
> }
>
> to look like this:
>
> {
>    err = v4l2_subdev_call(src_subdev, video, s_stream, true);
>    if (err < 0 && err != -ENOIOCTLCMD)
>      goto err_disable_csi_stream;
> ...
>    return 0;
>
> err_disable_csi_stream:
>    tegra_mipi_cancel_calibration(csi_chan->mipi);
>
>    v4l2_subdev_call(csi_subdev, video, s_stream, false);
>
>    return err;
> }
>
>
> It should make code a bit easier to read and follow.
>
> Otherwise this patch looks good to me, thanks.

Thanks Dmitry. Will send v7 now with this minor fix and would like to 
close on this soon.

Sowjanya