Re: [PATCH v5 03/10] media: i2c: ov6650: Use new [get|set]_mbus_config ops

From: Janusz Krzysztofik <jmkrzyszt@gmail.com>
To: mchehab@kernel.org, hverkuil-cisco@xs4all.nl,
	sakari.ailus@linux.intel.com, laurent.pinchart@ideasonboard.com,
	Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc: Jacopo Mondi <jacopo+renesas@jmondi.org>,
	niklas.soderlund+renesas@ragnatech.se,
	kieran.bingham@ideasonboard.com, dave.stevenson@raspberrypi.com,
	hyun.kwon@xilinx.com, linux-media@vger.kernel.org,
	linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH v5 03/10] media: i2c: ov6650: Use new [get|set]_mbus_config ops
Date: Sun, 21 Jun 2020 13:38:46 +0200	[thread overview]
Message-ID: <1837100.yKVeVyVuyW@z50> (raw)
In-Reply-To: <20200616141244.49407-4-jacopo+renesas@jmondi.org>

Hi Jacopo,

Thanks for bringing my attention to this patch.

On Tuesday, June 16, 2020 4:12:38 P.M. CEST Jacopo Mondi wrote:
> Use the new get_mbus_config and set_mbus_config pad operations in place
> of the video operations currently in use.
> 
> Compared to other drivers where the same conversion has been performed,
> ov6650 proved to be a bit more tricky, as the existing g_mbus_config
> implementation did not report the currently applied configuration but
> the set of all possible configuration options.

Assuming that was in line with officially supported semantics of the old API, 
not a misinterpretation, I would really like to see that limitation of the new 
API actually compensated with V4L2_SUBDEV_FORMAT_TRY support added to it.

> 
> Adapt the driver to support the semantic of the two newly introducedV4L2_SUBDEV_FORMAT_TRY
> operations:
> - get_mbus_config reports the current media bus configuration
> - set_mbus_config applies only changes explicitly requested and updates
>   the provided cfg parameter to report what has actually been applied to
>   the hardware.
> 
> Compile-tested only.
> 
> Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> ---
>  drivers/media/i2c/ov6650.c | 56 ++++++++++++++++++++++++++------------
>  1 file changed, 39 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov6650.c b/drivers/media/i2c/ov6650.c
> index 91906b94f978..d2e7a8556ed7 100644
> --- a/drivers/media/i2c/ov6650.c
> +++ b/drivers/media/i2c/ov6650.c
> @@ -921,46 +921,68 @@ static const struct v4l2_subdev_core_ops ov6650_core_ops = {
>  };
>  
>  /* Request bus settings on camera side */
> -static int ov6650_g_mbus_config(struct v4l2_subdev *sd,
> -				struct v4l2_mbus_config *cfg)
> +static int ov6650_get_mbus_config(struct v4l2_subdev *sd,
> +				  unsigned int pad,
> +				  struct v4l2_mbus_config *cfg)
>  {
> +	struct i2c_client *client = v4l2_get_subdevdata(sd);
> +	u8 comj, comf;
> +	int ret;
> +
> +	ret = ov6650_reg_read(client, REG_COMJ, &comj);
> +	if (ret)
> +		return ret;
>  
> -	cfg->flags = V4L2_MBUS_MASTER |
> -		V4L2_MBUS_PCLK_SAMPLE_RISING | V4L2_MBUS_PCLK_SAMPLE_FALLING |
> -		V4L2_MBUS_HSYNC_ACTIVE_HIGH | V4L2_MBUS_HSYNC_ACTIVE_LOW |
> -		V4L2_MBUS_VSYNC_ACTIVE_HIGH | V4L2_MBUS_VSYNC_ACTIVE_LOW |
> -		V4L2_MBUS_DATA_ACTIVE_HIGH;
> +	ret = ov6650_reg_read(client, REG_COMF, &comf);
> +	if (ret)
> +		return ret;
> +
> +	cfg->flags = V4L2_MBUS_MASTER
> +		   | ((comj & COMJ_VSYNC_HIGH)  ? V4L2_MBUS_VSYNC_ACTIVE_HIGH
> +						: V4L2_MBUS_VSYNC_ACTIVE_LOW)
> +		   | ((comf & COMF_HREF_LOW)    ? V4L2_MBUS_HSYNC_ACTIVE_LOW
> +						: V4L2_MBUS_HSYNC_ACTIVE_HIGH)
> +		   | ((comj & COMJ_PCLK_RISING) ? V4L2_MBUS_PCLK_SAMPLE_RISING
> +						: V4L2_MBUS_PCLK_SAMPLE_FALLING);

You probably missed hardware default V4L2_MBUS_DATA_ACTIVE_HIGH.

>  	cfg->type = V4L2_MBUS_PARALLEL;
>  
>  	return 0;
>  }
>  
>  /* Alter bus settings on camera side */
> -static int ov6650_s_mbus_config(struct v4l2_subdev *sd,
> -				const struct v4l2_mbus_config *cfg)
> +static int ov6650_set_mbus_config(struct v4l2_subdev *sd,
> +				  unsigned int pad,
> +				  struct v4l2_mbus_config *cfg)
>  {
>  	struct i2c_client *client = v4l2_get_subdevdata(sd);
> -	int ret;
> +	int ret = 0;
>  
>  	if (cfg->flags & V4L2_MBUS_PCLK_SAMPLE_RISING)
>  		ret = ov6650_reg_rmw(client, REG_COMJ, COMJ_PCLK_RISING, 0);
> -	else
> +	else if (cfg->flags & V4L2_MBUS_PCLK_SAMPLE_FALLING)

Have you thought of extending v4l2_subdev_call_pad_wrappers with a check for 
only one of mutually exclusive flags specified by user?

>  		ret = ov6650_reg_rmw(client, REG_COMJ, 0, COMJ_PCLK_RISING);
>  	if (ret)
> -		return ret;
> +		goto error;
>  
>  	if (cfg->flags & V4L2_MBUS_HSYNC_ACTIVE_LOW)
>  		ret = ov6650_reg_rmw(client, REG_COMF, COMF_HREF_LOW, 0);
> -	else
> +	else if (cfg->flags & V4L2_MBUS_HSYNC_ACTIVE_HIGH)
>  		ret = ov6650_reg_rmw(client, REG_COMF, 0, COMF_HREF_LOW);
>  	if (ret)
> -		return ret;
> +		goto error;
>  
>  	if (cfg->flags & V4L2_MBUS_VSYNC_ACTIVE_HIGH)
>  		ret = ov6650_reg_rmw(client, REG_COMJ, COMJ_VSYNC_HIGH, 0);
> -	else
> +	else if (cfg->flags & V4L2_MBUS_VSYNC_ACTIVE_LOW)
>  		ret = ov6650_reg_rmw(client, REG_COMJ, 0, COMJ_VSYNC_HIGH);
>  
> +error:
> +	/*
> +	 * Update the configuration to report what is actually applied to
> +	 * the hardware.
> +	 */
> +	ov6650_get_mbus_config(sd, pad, cfg);

Populating cfg->flags by ov6650_get_mbus_config() without checking for a 
potential error it may return can result in invalid data silently returned to 
user.  Maybe it would be better to fetch current hardware status first, fail on 
error, then update the result with successfully performed hardware state 
modifications.

Thanks,
Janusz

> +
>  	return ret;
>  }
>  
> @@ -968,8 +990,6 @@ static const struct v4l2_subdev_video_ops ov6650_video_ops = {
>  	.s_stream	= ov6650_s_stream,
>  	.g_frame_interval = ov6650_g_frame_interval,
>  	.s_frame_interval = ov6650_s_frame_interval,
> -	.g_mbus_config	= ov6650_g_mbus_config,
> -	.s_mbus_config	= ov6650_s_mbus_config,
>  };
>  
>  static const struct v4l2_subdev_pad_ops ov6650_pad_ops = {
> @@ -978,6 +998,8 @@ static const struct v4l2_subdev_pad_ops ov6650_pad_ops = {
>  	.set_selection	= ov6650_set_selection,
>  	.get_fmt	= ov6650_get_fmt,
>  	.set_fmt	= ov6650_set_fmt,
> +	.get_mbus_config = ov6650_get_mbus_config,
> +	.set_mbus_config = ov6650_set_mbus_config,
>  };
>  
>  static const struct v4l2_subdev_ops ov6650_subdev_ops = {
> 