Re: [PATCH v1 1/1] media: imx: csi: Parse link configuration from fw_node

[Dan Carpenter <dan.carpenter@linaro.org>]

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@mt.com>
> > ---
> >  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 };

> >  	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;

regards,
dan carpenter