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 14:39:01 +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 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?

> +	}
> +
...
>  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?

>  	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;
>  }
>  
>