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

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Message-ID: <f483329d-b5fe-fda5-e235-b8edb5fce440@nvidia.com>
Date:   Fri, 31 Jul 2020 08:46:36 -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 v6 09/10] media: tegra-video: Add CSI MIPI pads
 calibration


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.

>
>> +	}
>> +
> ...
>>   static int tegra_channel_enable_stream(struct tegra_vi_channel *chan)
>>   {
>>   	struct v4l2_subdev *csi_subdev, *src_subdev;
>> +	struct tegra_csi_channel *csi_chan;
>>   	int ret;
>>   
>>   	/*
>> @@ -206,13 +207,30 @@ static int tegra_channel_enable_stream(struct tegra_vi_channel *chan)
>>   	if (IS_ENABLED(CONFIG_VIDEO_TEGRA_TPG))
>>   		return 0;
>>   
>> +	csi_chan = v4l2_get_subdevdata(csi_subdev);
>> +	/*
>> +	 * TRM has incorrectly documented to wait for done status from
>> +	 * calibration logic after CSI interface power on.
>> +	 * As per the design, calibration results are latched and applied
>> +	 * to the pads only when the link is in LP11 state which will happen
>> +	 * during the sensor stream-on.
>> +	 * CSI subdev stream-on triggers start of MIPI pads calibration.
>> +	 * Wait for calibration to finish here after sensor subdev stream-on
>> +	 * and in case of sensor stream-on failure, cancel the calibration.
>> +	 */
>>   	src_subdev = tegra_channel_get_remote_source_subdev(chan);
> Is it possible to move the start_calibration() here?

I think we can do start here as well I guess but currently I am 
following steps order as per design document.

This is the reason I have updated in above comment as well.

>
>>   	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;
>>   	}
>>   
>> +	ret = tegra_mipi_finish_calibration(csi_chan->mipi);
>> +	if (ret < 0)
>> +		dev_warn(csi_chan->csi->dev,
>> +			 "MIPI calibration failed: %d\n", ret);
>> +
>>   	return 0;
>>   }
>>   
>>