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 19:14:36 +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, 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 v6 09/10] media: tegra-video: Add CSI MIPI pads
 calibration

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".