[v2] media: imx-mipi-csis: Get the number of active lanes from mbus_config

[PATCH v2 1/3] media: v4l: Add helper to get number of active lanes via a pad

Posted by Isaac Scott 5 months, 1 week ago

Sometimes, users will not use all of the MIPI CSI 2 lanes available when
connecting to the MIPI CSI receiver of their device. Add a helper
function that checks the mbus_config for the device driver to allow
users to define the number of active data lanes through the
get_mbus_config op.

If the driver does not implement this op, fall back to using the number
of data lanes specified in device tree.

Signed-off-by: Isaac Scott <isaac.scott@ideasonboard.com>
---
 drivers/media/v4l2-core/v4l2-common.c | 25 +++++++++++++++++++++++++
 include/media/v4l2-common.h           |  1 +
 2 files changed, 26 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
index 6e585bc76367..8683107b3704 100644
--- a/drivers/media/v4l2-core/v4l2-common.c
+++ b/drivers/media/v4l2-core/v4l2-common.c
@@ -571,6 +571,31 @@ s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
 	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
 }
 EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
+
+unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes)
+{
+	struct v4l2_mbus_config mbus_config = {};
+	struct v4l2_subdev *sd;
+	unsigned int lanes;
+	int ret;
+
+	sd = media_entity_to_v4l2_subdev(pad->entity);
+	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
+			       &mbus_config);
+	if (ret < 0 && ret != -ENOIOCTLCMD)
+		return ret;
+
+	if (!mbus_config.bus.mipi_csi2.num_data_lanes)
+		return dt_lanes;
+
+	lanes = mbus_config.bus.mipi_csi2.num_data_lanes;
+
+	if (lanes < 0 || lanes > dt_lanes)
+		return -EINVAL;
+
+	return lanes;
+}
+EXPORT_SYMBOL_GPL(v4l2_get_active_data_lanes);
 #endif /* CONFIG_MEDIA_CONTROLLER */
 
 /*
diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
index 0a43f56578bc..3f8937260c76 100644
--- a/include/media/v4l2-common.h
+++ b/include/media/v4l2-common.h
@@ -584,6 +584,7 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
 	(pad, mul, div)
 s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
 			     unsigned int div);
+unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes);
 #else
 #define v4l2_get_link_freq(handler, mul, div)		\
 	__v4l2_get_link_freq_ctrl(handler, mul, div)
-- 
2.43.0

Re: [PATCH v2 1/3] media: v4l: Add helper to get number of active lanes via a pad

Posted by Sakari Ailus 5 months, 1 week ago

Hi Isaac,

Thanks for the update.

On Wed, Sep 03, 2025 at 11:22:40AM +0100, Isaac Scott wrote:
> Sometimes, users will not use all of the MIPI CSI 2 lanes available when
> connecting to the MIPI CSI receiver of their device. Add a helper
> function that checks the mbus_config for the device driver to allow
> users to define the number of active data lanes through the
> get_mbus_config op.
> 
> If the driver does not implement this op, fall back to using the number
> of data lanes specified in device tree.
> 
> Signed-off-by: Isaac Scott <isaac.scott@ideasonboard.com>
> ---
>  drivers/media/v4l2-core/v4l2-common.c | 25 +++++++++++++++++++++++++
>  include/media/v4l2-common.h           |  1 +
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 6e585bc76367..8683107b3704 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -571,6 +571,31 @@ s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
>  	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
>  }
>  EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
> +
> +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes)

This line would benefit from being wrapped.

> +{
> +	struct v4l2_mbus_config mbus_config = {};
> +	struct v4l2_subdev *sd;
> +	unsigned int lanes;
> +	int ret;
> +
> +	sd = media_entity_to_v4l2_subdev(pad->entity);
> +	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
> +			       &mbus_config);
> +	if (ret < 0 && ret != -ENOIOCTLCMD)
> +		return ret;
> +
> +	if (!mbus_config.bus.mipi_csi2.num_data_lanes)
> +		return dt_lanes;
> +
> +	lanes = mbus_config.bus.mipi_csi2.num_data_lanes;
> +
> +	if (lanes < 0 || lanes > dt_lanes)

lanes is unsigned int so no need to check for less than 0.

I might just not use a local variable for this, up to you.

> +		return -EINVAL;
> +
> +	return lanes;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_get_active_data_lanes);
>  #endif /* CONFIG_MEDIA_CONTROLLER */
>  
>  /*
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 0a43f56578bc..3f8937260c76 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -584,6 +584,7 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
>  	(pad, mul, div)
>  s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
>  			     unsigned int div);

Some kernel-doc documentation would be nice.

> +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes);

Please wrap this, too.

>  #else
>  #define v4l2_get_link_freq(handler, mul, div)		\
>  	__v4l2_get_link_freq_ctrl(handler, mul, div)

-- 
Kind regards,

Sakari Ailus

Re: [PATCH v2 1/3] media: v4l: Add helper to get number of active lanes via a pad

Posted by Isaac Scott 4 months, 3 weeks ago

Hi Sakari,

Thank you for the review!

Quoting Sakari Ailus (2025-09-04 09:44:49)
> Hi Isaac,
> 
> Thanks for the update.
> 
> On Wed, Sep 03, 2025 at 11:22:40AM +0100, Isaac Scott wrote:
> > Sometimes, users will not use all of the MIPI CSI 2 lanes available when
> > connecting to the MIPI CSI receiver of their device. Add a helper
> > function that checks the mbus_config for the device driver to allow
> > users to define the number of active data lanes through the
> > get_mbus_config op.
> > 
> > If the driver does not implement this op, fall back to using the number
> > of data lanes specified in device tree.
> > 
> > Signed-off-by: Isaac Scott <isaac.scott@ideasonboard.com>
> > ---
> >  drivers/media/v4l2-core/v4l2-common.c | 25 +++++++++++++++++++++++++
> >  include/media/v4l2-common.h           |  1 +
> >  2 files changed, 26 insertions(+)
> > 
> > diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> > index 6e585bc76367..8683107b3704 100644
> > --- a/drivers/media/v4l2-core/v4l2-common.c
> > +++ b/drivers/media/v4l2-core/v4l2-common.c
> > @@ -571,6 +571,31 @@ s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
> >       return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
> >  }
> >  EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
> > +
> > +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes)
> 
> This line would benefit from being wrapped.

OK, I'll wrap it in v3.

> 
> > +{
> > +     struct v4l2_mbus_config mbus_config = {};
> > +     struct v4l2_subdev *sd;
> > +     unsigned int lanes;
> > +     int ret;
> > +
> > +     sd = media_entity_to_v4l2_subdev(pad->entity);
> > +     ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
> > +                            &mbus_config);
> > +     if (ret < 0 && ret != -ENOIOCTLCMD)
> > +             return ret;
> > +
> > +     if (!mbus_config.bus.mipi_csi2.num_data_lanes)
> > +             return dt_lanes;
> > +
> > +     lanes = mbus_config.bus.mipi_csi2.num_data_lanes;
> > +
> > +     if (lanes < 0 || lanes > dt_lanes)
> 
> lanes is unsigned int so no need to check for less than 0.
> 
> I might just not use a local variable for this, up to you.
> 
> > +             return -EINVAL;
> > +
> > +     return lanes;
> > +}
> > +EXPORT_SYMBOL_GPL(v4l2_get_active_data_lanes);
> >  #endif /* CONFIG_MEDIA_CONTROLLER */
> >  
> >  /*
> > diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> > index 0a43f56578bc..3f8937260c76 100644
> > --- a/include/media/v4l2-common.h
> > +++ b/include/media/v4l2-common.h
> > @@ -584,6 +584,7 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
> >       (pad, mul, div)
> >  s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
> >                            unsigned int div);
> 
> Some kernel-doc documentation would be nice.

Ah, of course, I'll include it in v3.

> 
> > +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes);
> 
> Please wrap this, too.

Will do!

> 
> >  #else
> >  #define v4l2_get_link_freq(handler, mul, div)                \
> >       __v4l2_get_link_freq_ctrl(handler, mul, div)
> 
> -- 
> Kind regards,
> 
> Sakari Ailus

Best wishes,

Isaac

Re: [PATCH v2 1/3] media: v4l: Add helper to get number of active lanes via a pad

Posted by Laurent Pinchart 5 months, 1 week ago

On Thu, Sep 04, 2025 at 11:44:49AM +0300, Sakari Ailus wrote:
> On Wed, Sep 03, 2025 at 11:22:40AM +0100, Isaac Scott wrote:
> > Sometimes, users will not use all of the MIPI CSI 2 lanes available when
> > connecting to the MIPI CSI receiver of their device. Add a helper
> > function that checks the mbus_config for the device driver to allow
> > users to define the number of active data lanes through the
> > get_mbus_config op.
> > 
> > If the driver does not implement this op, fall back to using the number
> > of data lanes specified in device tree.
> > 
> > Signed-off-by: Isaac Scott <isaac.scott@ideasonboard.com>
> > ---
> >  drivers/media/v4l2-core/v4l2-common.c | 25 +++++++++++++++++++++++++
> >  include/media/v4l2-common.h           |  1 +
> >  2 files changed, 26 insertions(+)
> > 
> > diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> > index 6e585bc76367..8683107b3704 100644
> > --- a/drivers/media/v4l2-core/v4l2-common.c
> > +++ b/drivers/media/v4l2-core/v4l2-common.c
> > @@ -571,6 +571,31 @@ s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
> >  	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
> >  }
> >  EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
> > +
> > +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes)
> 
> This line would benefit from being wrapped.

I'd also rename the dt_lanes parameter to max_data_lanes. "dt" sounds
like data type.

> > +{
> > +	struct v4l2_mbus_config mbus_config = {};
> > +	struct v4l2_subdev *sd;
> > +	unsigned int lanes;
> > +	int ret;
> > +
> > +	sd = media_entity_to_v4l2_subdev(pad->entity);
> > +	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
> > +			       &mbus_config);
> > +	if (ret < 0 && ret != -ENOIOCTLCMD)
> > +		return ret;
> > +
> > +	if (!mbus_config.bus.mipi_csi2.num_data_lanes)
> > +		return dt_lanes;
> > +
> > +	lanes = mbus_config.bus.mipi_csi2.num_data_lanes;
> > +
> > +	if (lanes < 0 || lanes > dt_lanes)
> 
> lanes is unsigned int so no need to check for less than 0.
> 
> I might just not use a local variable for this, up to you.
> 

A debug message would also be nice.

> > +		return -EINVAL;
> > +
> > +	return lanes;
> > +}
> > +EXPORT_SYMBOL_GPL(v4l2_get_active_data_lanes);
> >  #endif /* CONFIG_MEDIA_CONTROLLER */
> >  
> >  /*
> > diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> > index 0a43f56578bc..3f8937260c76 100644
> > --- a/include/media/v4l2-common.h
> > +++ b/include/media/v4l2-common.h
> > @@ -584,6 +584,7 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
> >  	(pad, mul, div)
> >  s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
> >  			     unsigned int div);
> 
> Some kernel-doc documentation would be nice.
> 
> > +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes);
> 
> Please wrap this, too.
> 
> >  #else
> >  #define v4l2_get_link_freq(handler, mul, div)		\
> >  	__v4l2_get_link_freq_ctrl(handler, mul, div)

-- 
Regards,

Laurent Pinchart

Re: [PATCH v2 1/3] media: v4l: Add helper to get number of active lanes via a pad

Posted by Niklas Söderlund 5 months, 1 week ago

Hi Issac,

Thanks for your work.

On 2025-09-03 11:22:40 +0100, Isaac Scott wrote:
> Sometimes, users will not use all of the MIPI CSI 2 lanes available when
> connecting to the MIPI CSI receiver of their device. Add a helper
> function that checks the mbus_config for the device driver to allow
> users to define the number of active data lanes through the
> get_mbus_config op.
> 
> If the driver does not implement this op, fall back to using the number
> of data lanes specified in device tree.
> 
> Signed-off-by: Isaac Scott <isaac.scott@ideasonboard.com>
> ---
>  drivers/media/v4l2-core/v4l2-common.c | 25 +++++++++++++++++++++++++
>  include/media/v4l2-common.h           |  1 +
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 6e585bc76367..8683107b3704 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -571,6 +571,31 @@ s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
>  	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
>  }
>  EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
> +
> +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes)
> +{
> +	struct v4l2_mbus_config mbus_config = {};
> +	struct v4l2_subdev *sd;
> +	unsigned int lanes;
> +	int ret;
> +
> +	sd = media_entity_to_v4l2_subdev(pad->entity);
> +	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
> +			       &mbus_config);
> +	if (ret < 0 && ret != -ENOIOCTLCMD)
> +		return ret;

The function prototype is 'unsigned int' and here you return a signed 
value here.

> +

Maybe add a comment here that this check depends on mbus_config being 
zeroed at init if the call above pass with -ENOIOCTLCMD? It's not 
immediately clear what is going on here even tho the code is clever ;-)

> +	if (!mbus_config.bus.mipi_csi2.num_data_lanes)
> +		return dt_lanes;
> +
> +	lanes = mbus_config.bus.mipi_csi2.num_data_lanes;
> +
> +	if (lanes < 0 || lanes > dt_lanes)
> +		return -EINVAL;
> +
> +	return lanes;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_get_active_data_lanes);
>  #endif /* CONFIG_MEDIA_CONTROLLER */
>  
>  /*
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 0a43f56578bc..3f8937260c76 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -584,6 +584,7 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
>  	(pad, mul, div)
>  s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
>  			     unsigned int div);
> +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes);
>  #else
>  #define v4l2_get_link_freq(handler, mul, div)		\
>  	__v4l2_get_link_freq_ctrl(handler, mul, div)
> -- 
> 2.43.0
> 

-- 
Kind Regards,
Niklas Söderlund

Re: [PATCH v2 1/3] media: v4l: Add helper to get number of active lanes via a pad

Posted by Frank Li 5 months, 1 week ago

On Wed, Sep 03, 2025 at 11:22:40AM +0100, Isaac Scott wrote:
> Sometimes, users will not use all of the MIPI CSI 2 lanes available when
> connecting to the MIPI CSI receiver of their device. Add a helper
> function that checks the mbus_config for the device driver to allow
> users to define the number of active data lanes through the
> get_mbus_config op.
>
> If the driver does not implement this op, fall back to using the number
> of data lanes specified in device tree.
>
> Signed-off-by: Isaac Scott <isaac.scott@ideasonboard.com>

Reviewed-by: Frank Li <Frank.Li@nxp.com>
> ---
>  drivers/media/v4l2-core/v4l2-common.c | 25 +++++++++++++++++++++++++
>  include/media/v4l2-common.h           |  1 +
>  2 files changed, 26 insertions(+)
>
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 6e585bc76367..8683107b3704 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -571,6 +571,31 @@ s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
>  	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
>  }
>  EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
> +
> +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes)
> +{
> +	struct v4l2_mbus_config mbus_config = {};
> +	struct v4l2_subdev *sd;
> +	unsigned int lanes;
> +	int ret;
> +
> +	sd = media_entity_to_v4l2_subdev(pad->entity);
> +	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
> +			       &mbus_config);
> +	if (ret < 0 && ret != -ENOIOCTLCMD)
> +		return ret;
> +
> +	if (!mbus_config.bus.mipi_csi2.num_data_lanes)
> +		return dt_lanes;
> +
> +	lanes = mbus_config.bus.mipi_csi2.num_data_lanes;
> +
> +	if (lanes < 0 || lanes > dt_lanes)
> +		return -EINVAL;
> +
> +	return lanes;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_get_active_data_lanes);
>  #endif /* CONFIG_MEDIA_CONTROLLER */
>
>  /*
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 0a43f56578bc..3f8937260c76 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -584,6 +584,7 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat,
>  	(pad, mul, div)
>  s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
>  			     unsigned int div);
> +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes);
>  #else
>  #define v4l2_get_link_freq(handler, mul, div)		\
>  	__v4l2_get_link_freq_ctrl(handler, mul, div)
> --
> 2.43.0
>