linux-kernel - Re: [PATCH 13/13] media: i2c: ov5647: Add V4L2_CID_LINK

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Message-ID: <tca3pwpzwqokxpjlv5mjsf3mai6ojlwypve6np53vur4cojd3t@viistqpnzv25>
Date: Sun, 2 Nov 2025 12:29:02 +0100
From: Jacopo Mondi <jacopo.mondi@...asonboard.com>
To: Jai Luthra <jai.luthra@...asonboard.com>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Dave Stevenson <dave.stevenson@...pberrypi.com>, Jacopo Mondi <jacopo@...ndi.org>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Mauro Carvalho Chehab <mchehab+huawei@...nel.org>, Kieran Bingham <kieran.bingham@...asonboard.com>, 
	David Plowman <david.plowman@...pberrypi.com>, Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Peter Robinson <pbrobinson@...il.com>, Stefan Wahren <wahrenst@....net>, 
	"Ivan T. Ivanov" <iivanov@...e.de>
Subject: Re: [PATCH 13/13] media: i2c: ov5647: Add V4L2_CID_LINK_FREQUENCY
 control

Hi Jai

On Tue, Oct 28, 2025 at 12:57:24PM +0530, Jai Luthra wrote:
> From: Dave Stevenson <dave.stevenson@...pberrypi.com>
>
> The link frequency can vary between modes, so add it as a
> control.
>
> Signed-off-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> Signed-off-by: Jai Luthra <jai.luthra@...asonboard.com>
> ---
>  drivers/media/i2c/ov5647.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/i2c/ov5647.c b/drivers/media/i2c/ov5647.c
> index be0b96c4372ae0c6d8fc57280b195d6069dd7019..dea978305c3c868819780f7f631b225f4c1e7756 100644
> --- a/drivers/media/i2c/ov5647.c
> +++ b/drivers/media/i2c/ov5647.c
> @@ -97,6 +97,13 @@ static const char * const ov5647_supply_names[] = {
>
>  #define OV5647_NUM_SUPPLIES ARRAY_SIZE(ov5647_supply_names)
>
> +#define FREQ_INDEX_FULL		0
> +#define FREQ_INDEX_VGA		1
> +static const s64 ov5647_link_freqs[] = {
> +	[FREQ_INDEX_FULL]	= 218500000,

The full mode pixel rate is set to 87500000, which considering CSI-2
DDR mode and the 2 lanes in use give me a link freq of 21875000.

Do you know where 218500000 comes from ? (it might be perfectly legit,
I'm not questioning that).

> +	[FREQ_INDEX_VGA]	= 208333000,
> +};
> +
>  struct regval_list {
>  	u16 addr;
>  	u8 data;
> @@ -106,6 +113,7 @@ struct ov5647_mode {
>  	struct v4l2_mbus_framefmt	format;
>  	struct v4l2_rect		crop;
>  	u64				pixel_rate;
> +	unsigned int			link_freq_index;
>  	int				hts;
>  	int				vts;
>  	const struct regval_list	*reg_list;
> @@ -128,6 +136,7 @@ struct ov5647 {
>  	struct v4l2_ctrl		*exposure;
>  	struct v4l2_ctrl		*hflip;
>  	struct v4l2_ctrl		*vflip;
> +	struct v4l2_ctrl		*link_freq;
>  };
>
>  static inline struct ov5647 *to_sensor(struct v4l2_subdev *sd)
> @@ -376,6 +385,7 @@ static const struct ov5647_mode ov5647_modes[] = {
>  			.height		= 1944
>  		},
>  		.pixel_rate	= 87500000,
> +		.link_freq_index = FREQ_INDEX_FULL,
>  		.hts		= 2844,
>  		.vts		= 0x7b0,
>  		.reg_list	= ov5647_2592x1944_10bpp,
> @@ -397,6 +407,7 @@ static const struct ov5647_mode ov5647_modes[] = {
>  			.height		= 1080,
>  		},
>  		.pixel_rate	= 87500000,
> +		.link_freq_index = FREQ_INDEX_FULL,
>  		.hts		= 2416,
>  		.vts		= 0x450,
>  		.reg_list	= ov5647_1080p30_10bpp,
> @@ -418,6 +429,7 @@ static const struct ov5647_mode ov5647_modes[] = {
>  			.height		= 1944,
>  		},
>  		.pixel_rate	= 87500000,
> +		.link_freq_index = FREQ_INDEX_FULL,
>  		.hts		= 1896,
>  		.vts		= 0x59b,
>  		.reg_list	= ov5647_2x2binned_10bpp,
> @@ -439,6 +451,7 @@ static const struct ov5647_mode ov5647_modes[] = {
>  			.height		= 1920,
>  		},
>  		.pixel_rate	= 55000000,
> +		.link_freq_index = FREQ_INDEX_VGA,
>  		.hts		= 1852,
>  		.vts		= 0x1f8,
>  		.reg_list	= ov5647_640x480_10bpp,
> @@ -925,6 +938,8 @@ static int ov5647_set_pad_fmt(struct v4l2_subdev *sd,
>  					 sensor->exposure->minimum,
>  					 exposure_max, sensor->exposure->step,
>  					 exposure_def);
> +
> +		__v4l2_ctrl_s_ctrl(sensor->link_freq, mode->link_freq_index);

Doesn't this cause an error in s_ctrl where the control is not handled
?

>  	}
>  	*fmt = mode->format;
>  	/* The code we pass back must reflect the current h/vflips. */
> @@ -1230,7 +1245,7 @@ static int ov5647_init_controls(struct ov5647 *sensor, struct device *dev)
>  	int hblank, exposure_max, exposure_def;
>  	struct v4l2_fwnode_device_properties props;
>
> -	v4l2_ctrl_handler_init(&sensor->ctrls, 9);
> +	v4l2_ctrl_handler_init(&sensor->ctrls, 10);
>
>  	v4l2_ctrl_new_std(&sensor->ctrls, &ov5647_ctrl_ops,
>  			  V4L2_CID_AUTOGAIN, 0, 1, 1, 0);
> @@ -1290,6 +1305,14 @@ static int ov5647_init_controls(struct ov5647 *sensor, struct device *dev)
>  	if (sensor->vflip)
>  		sensor->vflip->flags |= V4L2_CTRL_FLAG_MODIFY_LAYOUT;
>
> +	sensor->link_freq =
> +		v4l2_ctrl_new_int_menu(&sensor->ctrls, &ov5647_ctrl_ops,

As suggested for PIXEL_RATE, if you make the control read-only you
should set the control ops to NULL.
> +				       V4L2_CID_LINK_FREQ,
> +				       ARRAY_SIZE(ov5647_link_freqs) - 1, 0,
> +				       ov5647_link_freqs);
> +	if (sensor->link_freq)
> +		sensor->link_freq->flags |= V4L2_CTRL_FLAG_READ_ONLY;

You know, I thought link_freq was set as READ_ONLY by the framework,
but it's actuallt PIXEL_RATE (you can remove setting the flags
in the driver if you send a patch to remove the control ops when
registering PIXEL_RATE).

Thanks
  j

> +
>  	v4l2_fwnode_device_parse(dev, &props);
>
>  	v4l2_ctrl_new_fwnode_properties(&sensor->ctrls, &ov5647_ctrl_ops,
>
> --
> 2.51.0
>