Re: [PATCH v8 2/9] media: v4l: Support obtaining link frequency via get_mbus_config

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Moi,

On Fri, Dec 20, 2024 at 02:59:39PM +0200, Tomi Valkeinen wrote:
> Hi,
> 
> On 17/12/2024 23:54, Sakari Ailus wrote:
> > Add link_freq field to struct v4l2_mbus_config in order to pass the link
> > frequency to the receiving sub-device.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > ---
> >   drivers/media/v4l2-core/v4l2-common.c | 15 +++++++++++++--
> >   include/media/v4l2-mediabus.h         |  2 ++
> >   2 files changed, 15 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> > index 9fe74c7e064f..e4b2de3833ee 100644
> > --- a/drivers/media/v4l2-core/v4l2-common.c
> > +++ b/drivers/media/v4l2-core/v4l2-common.c
> > @@ -508,12 +508,23 @@ EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_ctrl);
> >   s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
> >   			     unsigned int div)
> >   {
> > +	struct v4l2_mbus_config mbus_config = {};
> >   	struct v4l2_subdev *sd;
> > +	int ret;
> >   	sd = media_entity_to_v4l2_subdev(pad->entity);
> > -	if (!sd)
> > -		return -ENODEV;
> > +	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
> > +			       &mbus_config);
> > +	if (ret < 0 && ret != -ENOIOCTLCMD)
> > +		return ret;
> > +
> > +	if (mbus_config.link_freq)
> > +		return mbus_config.link_freq;
> > +	/*
> > +	 * Fall back to using the link frequency control if the media bus config
> > +	 * doesn't provide a link frequency.
> > +	 */
> >   	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
> >   }
> >   EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
> > diff --git a/include/media/v4l2-mediabus.h b/include/media/v4l2-mediabus.h
> > index e7f019f68c8d..24c738cd7894 100644
> > --- a/include/media/v4l2-mediabus.h
> > +++ b/include/media/v4l2-mediabus.h
> > @@ -169,6 +169,7 @@ enum v4l2_mbus_type {
> >   /**
> >    * struct v4l2_mbus_config - media bus configuration
> >    * @type: interface type
> > + * @link_freq: The link frequency. See also V4L2_CID_LINK_FREQ control.
> >    * @bus: bus configuration data structure
> >    * @bus.parallel: embedded &struct v4l2_mbus_config_parallel.
> >    *		  Used if the bus is parallel or BT.656.
> > @@ -183,6 +184,7 @@ enum v4l2_mbus_type {
> >    */
> >   struct v4l2_mbus_config {
> >   	enum v4l2_mbus_type type;
> > +	u64 link_freq;
> >   	union {
> >   		struct v4l2_mbus_config_parallel parallel;
> >   		struct v4l2_mbus_config_mipi_csi1 mipi_csi1;
> 
> Maybe the docs (V4L2_CID_LINK_FREQ and/or struct v4l2_mbus_config?) should
> mention that only if v4l2_mbus_config.link_freq is == 0, V4L2_CID_LINK_FREQ
> is used. Or, in other words, the driver must only use one of those methods.

Such documentation is added by the 3rd patch ("media: Documentation: Update link frequency driver
documentation"):

diff --git a/Documentation/driver-api/media/tx-rx.rst b/Documentation/driver-api/media/tx-rx.rst
index c71003f74b1c..6f9eba189a9f 100644
--- a/Documentation/driver-api/media/tx-rx.rst
+++ b/Documentation/driver-api/media/tx-rx.rst
@@ -49,6 +49,10 @@ Link frequency
 The :ref:`V4L2_CID_LINK_FREQ <v4l2-cid-link-freq>` control is used to tell the
 receiver the frequency of the bus (i.e. it is not the same as the symbol rate).
 
+Drivers that do not have user-configurable link frequency should report it
+through the ``.get_mbus_config()`` subdev pad operation, in the ``link_freq``
+field of struct v4l2_mbus_config, instead of through controls.
+
 ``.enable_streams()`` and ``.disable_streams()`` callbacks
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

-- 
Sakari Ailus