Hi Dan,
On Thu, Mar 06, 2025 at 10:07:20PM +0300, Dan Carpenter wrote:
> On Thu, Mar 06, 2025 at 04:33:18PM +0000, Sakari Ailus wrote:
> > Hi Mathis,
> >
> > Thanks for the patch.
> >
> > On Wed, Mar 05, 2025 at 12:38:02PM +0100, Mathis Foerst wrote:
> > > The imx-media-csi driver requires upstream camera drivers to implement
> > > the subdev-pad-op "get_mbus_config" [0]. Camera drivers that don't
> > > implement this function are not usable on the i.MX6.
> > >
> > > The docs for get_mbus_config [1] say:
> > > @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.
> > >
> > > Currently, the imx-media-csi driver is not incorporating the information
> > > from the firmware interface and therefore relies on the implementation of
> > > get_mbus_config by the camera driver.
> > >
> > > To be compatible with camera drivers not implementing get_mbus_config
> > > (which is the usual case), use the bus information from the fw interface:
> > >
> > > The camera does not necessarily has a direct media bus link to the CSI as
> > > the video-mux and/or the MIPI CSI-2 receiver of the i.MX6 might be in
> > > between them on the media pipeline.
> > > The CSI driver already implements the functionality to find the connected
> > > camera sub-device to call get_mbus_config on it.
> > >
> > > At this point the driver is modified as follows:
> > > In the case that get_mbus_config is not implemented by the upstream
> > > camera, try to get its endpoint configuration from the firmware interface
> > > usign v4l2_fwnode_endpoint_parse.
> > > For the supported mbus_types (V4L2_MBUS_PARALLEL, V4L2_MBUS_BT656 and
> > > V4L2_MBUS_CSI2_DPHY), extract the mbus_config from the endpoint
> > > configuration.
> > > For all other mbus_types, return an error.
> > >
> > > Note that parsing the mbus_config from the fw interface is not done during
> > > probing because the camera that's connected to the CSI can change based on
> > > the selected input of the video-mux at runtime.
> > >
> > > [0] drivers/staging/media/imx/imx-media-csi.c - line 211..216
> > > [1] include/media/v4l2-subdev.h - line 814
> > >
> > > Signed-off-by: Mathis Foerst <mathis.foerst@xxxxxx>
> > > ---
> > > drivers/staging/media/imx/imx-media-csi.c | 36 ++++++++++++++++++++---
> > > 1 file changed, 32 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
> > > index 3edbc57be2ca..394a9321a10b 100644
> > > --- a/drivers/staging/media/imx/imx-media-csi.c
> > > +++ b/drivers/staging/media/imx/imx-media-csi.c
> > > @@ -169,6 +169,8 @@ static int csi_get_upstream_mbus_config(struct csi_priv *priv,
> > > {
> > > struct v4l2_subdev *sd, *remote_sd;
> > > struct media_pad *remote_pad;
> > > + struct fwnode_handle *ep_node;
> > > + struct v4l2_fwnode_endpoint ep = { .bus_type = 0 };
> >
> > Are there any defaults in DT bindings (other than 0's)? Also initialising a
> > field to zero this way is redundant, just use {}.
> >
>
> I was going to respond in much the same way. This is equivalen to:
>
> struct v4l2_fwnode_endpoint ep = { .bus_type = V4L2_MBUS_UNKNOWN };
Thinking about this in a context of parsing the endpoint, in fact the
bus_type should be specified. Presumably the hardware is D-PHY, so the
correct value would be V4L2_MBUS_CSI2_DPHY. This way
v4l2_fwnode_endpoint_parse() doesn't need to guess.
>
> > > int ret;
> > >
> > > if (!priv->src_sd)
> > > @@ -210,11 +212,37 @@ static int csi_get_upstream_mbus_config(struct csi_priv *priv,
> > >
> > > ret = v4l2_subdev_call(remote_sd, pad, get_mbus_config,
> > > remote_pad->index, mbus_cfg);
> > > - if (ret == -ENOIOCTLCMD)
> > > - v4l2_err(&priv->sd,
> > > - "entity %s does not implement get_mbus_config()\n",
> > > - remote_pad->entity->name);
> > > + if (ret == -ENOIOCTLCMD) {
> >
> > if (!ret)
> > return 0;
> >
> > And you can unindent the rest.
>
> I was going to say this too but then I thought actually this needs to
> be:
>
> if (ret != -ENOIOCTLCMD)
> return ret;
>
> Which is weird. Better to break all the new code into a separate
> helper function.
>
> if (ret == -ENOIOCTLCMD)
> ret = parse_fw_link_config_stuff();
>
> return ret;
Indeed. get_mbus_config() presumably wouldn't return an error but
correctness is usually a good idea.
--
Regards,
Sakari Ailus
