Hi Hans,
On Wednesday, July 15, 2020 5:08:05 P.M. CEST Hans Verkuil wrote:
> On 14/07/2020 15:58, Jacopo Mondi wrote:
> > Introduce two new pad operations to allow retrieving and configuring the
> > media bus parameters on a subdevice pad.
> >
> > The newly introduced operations aims to replace the s/g_mbus_config video
> > operations, which have been on their way for deprecation since a long
> > time.
> >
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
> > ---
> > include/media/v4l2-subdev.h | 27 +++++++++++++++++++++++++++
> > 1 file changed, 27 insertions(+)
> >
> > diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> > index f7fe78a6f65a..d8b9d5735307 100644
> > --- a/include/media/v4l2-subdev.h
> > +++ b/include/media/v4l2-subdev.h
> > @@ -670,6 +670,29 @@ struct v4l2_subdev_pad_config {
> > *
> > * @set_frame_desc: set the low level media bus frame parameters, @fd array
> > * may be adjusted by the subdev driver to device capabilities.
> > + *
> > + * @get_mbus_config: get the media bus configuration of a remote sub-device.
> > + * The media bus configuration is usually retrieved from the
> > + * firmware interface at sub-device probe time, immediately
> > + * applied to the hardware and eventually adjusted by the
> > + * driver. Remote sub-devices (usually video receivers) shall
> > + * use this operation to query the transmitting end bus
> > + * configuration in order to adjust their own one accordingly.
> > + * Callers should make sure they get the most up-to-date as
> > + * possible configuration from the remote end, likely calling
> > + * this operation as close as possible to stream on time. The
> > + * operation shall fail if the pad index it has been called on
> > + * is not valid.
> > + *
> > + * @set_mbus_config: set the media bus configuration of a remote sub-device.
> > + * This operations is intended to allow, in combination with
> > + * the get_mbus_config operation, the negotiation of media bus
> > + * configuration parameters between media sub-devices. The
> > + * operation shall not fail if the requested configuration is
> > + * not supported, but the driver shall update the content of
> > + * the %config argument to reflect what has been actually
> > + * applied to the hardware. The operation shall fail if the
> > + * pad index it has been called on is not valid.
> > */
>
> Hm, I'd hoped I could merge this, but I think include/media/v4l2-mediabus.h
> also needs to be updated.
>
> So the old g_mbus_config returned all supported configurations, while the
> new get_mbus_config returns the *current* configuration.
>
> That's fine, but that means that the meaning of the struct v4l2_mbus_config
> flags field changes as well and several comments in v4l2-mediabus.h need to
> be updated to reflect this.
>
> E.g. instead of '/* How many lanes the client can use */' it becomes
> '/* How many lanes the client uses */'.
>
> Frankly, these flags can be redesigned now since you only need a single
> e.g. V4L2_MBUS_HSYNC_ACTIVE_HIGH flag since if it is not set, then that
> means ACTIVE_LOW. And since it is now a single bit, it is also easy to
> make each flag a bit field.
Even if this makes sense for .get_mbus_config() which returns current
configuration, how about keeping the old semantics of the flags and let
.set_mbus_config() accept a potentially incomplete or redundant set of flags
specified by the caller to select a supported configuration from? That approach
was actually proposed before by Jacopo when he argued against my suggestion to
add a wrapper with a check for mutually exclusive flags[1], and I found it a
very good alternative to my other rejected suggestion of adding TRY support.
[1] https://www.spinics.net/lists/linux-media/msg171878.html
Thanks,
Janusz
>
> The CSI2 lanes/channels can just be a bit field for the number of lanes/channels,
> which is much easier to read. I strongly recommend making this change at the minimum.
>
> Now all this can be done in a follow-up series, but the v4l2-mediabus.h
> definitely needs to be updated to reflect the new code.
>
> This can be done as a v6 5.5/9 patch (since it should come right after the
> g/s_mbus_config removal).
>
> Regards,
>
> Hans
>
> > struct v4l2_subdev_pad_ops {
> > int (*init_cfg)(struct v4l2_subdev *sd,
> > @@ -710,6 +733,10 @@ struct v4l2_subdev_pad_ops {
> > struct v4l2_mbus_frame_desc *fd);
> > int (*set_frame_desc)(struct v4l2_subdev *sd, unsigned int pad,
> > struct v4l2_mbus_frame_desc *fd);
> > + int (*get_mbus_config)(struct v4l2_subdev *sd, unsigned int pad,
> > + struct v4l2_mbus_config *config);
> > + int (*set_mbus_config)(struct v4l2_subdev *sd, unsigned int pad,
> > + struct v4l2_mbus_config *config);
> > };
> >
> > /**
> >
>
>
