Re: [PATCH v10 03/14] media: v4l2-fwnode: add initial connector parsing support

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

Hi Marco,

On Wed, Nov 27, 2019 at 09:26:16AM +0100, Marco Felsch wrote:
> Hi Sakari,
> 
> this is a gentle ping and I've added a comment inline.
> 
> On 19-11-19 12:15, Marco Felsch wrote:
> > Hi Sakari,
> > 
> > many thanks for the review :)
> > 
> > On 19-11-16 01:06, Sakari Ailus wrote:
> > > Hi Marco,
> > > 
> > > On Fri, Nov 08, 2019 at 09:58:52AM +0100, Marco Felsch wrote:
> > > > Hi Sakari,
> > > > 
> > > > sorry for my delay now ^^
> > > > 
> > > > On 19-10-24 15:02, Sakari Ailus wrote:
> > > > > Hi Marco,
> > > > > 
> > > > > On Wed, Oct 23, 2019 at 02:21:57PM +0200, Marco Felsch wrote:
> > > > > > Hi Sakari,
> > > > > > 
> > > > > > On 19-10-23 13:57, Sakari Ailus wrote:
> > > > > > > Hi Marco,
> > > > > > > 
> > > > > > > Apologies for the delay.
> > > > > > 
> > > > > > No problem.
> > > > > > 
> > > > > > > On Wed, Oct 02, 2019 at 10:07:35AM +0200, Marco Felsch wrote:
> > > > > > > > Hi Sakari,
> > > > > > > > 
> > > > > > > > On 19-10-02 10:03, Sakari Ailus wrote:
> > > > > > > > > Hi Marco,
> > > > > > > > > 
> > > > > > > > > On Fri, Aug 30, 2019 at 12:16:35PM +0200, Marco Felsch wrote:
> > > > > > > > > > The patch adds the initial connector parsing code, so we can move from a
> > > > > > > > > > driver specific parsing code to a generic one. Currently only the
> > > > > > > > > > generic fields and the analog-connector specific fields are parsed. Parsing
> > > > > > > > > > the other connector specific fields can be added by a simple callbacks.
> > > > > > > > > > 
> > > > > > > > > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > > > > > > > > > ---
> > > > > > > > > > [1] https://patchwork.kernel.org/cover/10794703/
> > > > > > > > > > 
> > > > > > > > > > v10:
> > > > > > > > > > - drop V4L2_CONN_HDMI support
> > > > > > > > > > - adapt pr_err msg to reflect new state (-> connector is unkown)
> > > > > > > > > > 
> > > > > > > > > > v9:
> > > > > > > > > > - Fix leading semicolon found by kbuild semicolon.cocci
> > > > > > > > > > 
> > > > > > > > > > v8:
> > > > > > > > > > - V4L2_CON_* -> V4L2_CONN_*
> > > > > > > > > > - tvnorms -> sdtv-standards
> > > > > > > > > > - adapt to new v4l2_fwnode_connector_analog member
> > > > > > > > > > - return error in case of V4L2_CONN_HDMI
> > > > > > > > > > 
> > > > > > > > > > v7:
> > > > > > > > > > @Jacopo: I dropped your r b tag becuase of the amount of changes I
> > > > > > > > > > made..
> > > > > > > > > > 
> > > > > > > > > > - drop unnecessary comments
> > > > > > > > > > - fix commet style
> > > > > > > > > > - s/v4l2_fwnode_connector_conv.name/v4l2_fwnode_connector_conv.compatible/
> > > > > > > > > > - make label size variable and drop V4L2_CONNECTOR_MAX_LABEL usage
> > > > > > > > > > - do not assign a default label in case of no label was specified
> > > > > > > > > > - remove useless /* fall through */ comments
> > > > > > > > > > - add support for N connector links
> > > > > > > > > > - rename local variables to be more meaningful
> > > > > > > > > > - adjust kernedoc
> > > > > > > > > > - add v4l2_fwnode_connector_free()
> > > > > > > > > > - improve error handling (use different error values)
> > > > > > > > > > - make use of pr_warn_once()
> > > > > > > > > > 
> > > > > > > > > > v6:
> > > > > > > > > > - use unsigned count var
> > > > > > > > > > - fix comment and style issues
> > > > > > > > > > - place '/* fall through */' to correct places
> > > > > > > > > > - fix error handling and cleanup by releasing fwnode
> > > > > > > > > > - drop vga and dvi parsing support as those connectors are rarely used
> > > > > > > > > >   these days
> > > > > > > > > > 
> > > > > > > > > > v5:
> > > > > > > > > > - s/strlcpy/strscpy/
> > > > > > > > > > 
> > > > > > > > > > v2-v4:
> > > > > > > > > > - nothing since the patch was squashed from series [1] into this
> > > > > > > > > >   series.
> > > > > > > > > > 
> > > > > > > > > >  drivers/media/v4l2-core/v4l2-fwnode.c | 129 ++++++++++++++++++++++++++
> > > > > > > > > >  include/media/v4l2-fwnode.h           |  38 ++++++++
> > > > > > > > > >  2 files changed, 167 insertions(+)
> > > > > > > > > > 
> > > > > > > > > > diff --git a/drivers/media/v4l2-core/v4l2-fwnode.c b/drivers/media/v4l2-core/v4l2-fwnode.c
> > > > > > > > > > index 3bd1888787eb..0bfa7cbf78df 100644
> > > > > > > > > > --- a/drivers/media/v4l2-core/v4l2-fwnode.c
> > > > > > > > > > +++ b/drivers/media/v4l2-core/v4l2-fwnode.c
> > > > > > > > > > @@ -595,6 +595,135 @@ void v4l2_fwnode_put_link(struct v4l2_fwnode_link *link)
> > > > > > > > > >  }
> > > > > > > > > >  EXPORT_SYMBOL_GPL(v4l2_fwnode_put_link);
> > > > > > > > > >  
> > > > > > > > > > +static const struct v4l2_fwnode_connector_conv {
> > > > > > > > > > +	enum v4l2_connector_type type;
> > > > > > > > > > +	const char *compatible;
> > > > > > > > > > +} connectors[] = {
> > > > > > > > > > +	{
> > > > > > > > > > +		.type = V4L2_CONN_COMPOSITE,
> > > > > > > > > > +		.compatible = "composite-video-connector",
> > > > > > > > > > +	}, {
> > > > > > > > > > +		.type = V4L2_CONN_SVIDEO,
> > > > > > > > > > +		.compatible = "svideo-connector",
> > > > > > > > > > +	},
> > > > > > > > > > +};
> > > > > > > > > > +
> > > > > > > > > > +static enum v4l2_connector_type
> > > > > > > > > > +v4l2_fwnode_string_to_connector_type(const char *con_str)
> > > > > > > > > > +{
> > > > > > > > > > +	unsigned int i;
> > > > > > > > > > +
> > > > > > > > > > +	for (i = 0; i < ARRAY_SIZE(connectors); i++)
> > > > > > > > > > +		if (!strcmp(con_str, connectors[i].compatible))
> > > > > > > > > > +			return connectors[i].type;
> > > > > > > > > > +
> > > > > > > > > > +	return V4L2_CONN_UNKNOWN;
> > > > > > > > > > +}
> > > > > > > > > > +
> > > > > > > > > > +static int
> > > > > > > > > > +v4l2_fwnode_connector_parse_analog(struct fwnode_handle *fwnode,
> > > > > > > > > > +				   struct v4l2_fwnode_connector *vc)
> > > > > > > > > > +{
> > > > > > > > > > +	u32 stds;
> > > > > > > > > > +	int ret;
> > > > > > > > > > +
> > > > > > > > > > +	ret = fwnode_property_read_u32(fwnode, "sdtv-standards", &stds);
> > > > > > > > > > +
> > > > > > > > > > +	/* The property is optional. */
> > > > > > > > > > +	vc->connector.analog.sdtv_stds = ret ? V4L2_STD_ALL : stds;
> > > > > > > > > > +
> > > > > > > > > > +	return 0;
> > > > > > > > > > +}
> > > > > > > > > > +
> > > > > > > > > > +void v4l2_fwnode_connector_free(struct v4l2_fwnode_connector *connector)
> > > > > > > > > > +{
> > > > > > > > > > +	unsigned int i;
> > > > > > > > > > +
> > > > > > > > > > +	if (IS_ERR_OR_NULL(connector))
> > > > > > > > > > +		return;
> > > > > > > > > > +
> > > > > > > > > > +	for (i = 0; i < connector->nr_of_links; i++)
> > > > > > > > > > +		v4l2_fwnode_put_link(&connector->links[i]);
> > > > > > > > > > +	kfree(connector->links);
> > > > > > > > > 
> > > > > > > > > Please assign connector->links NULL here, and nr_of_links to zero.
> > > > > > > > 
> > > > > > > > Okay, I can do that.
> > > > > > > > 
> > > > > > > > > > +}
> > > > > > > > > > +EXPORT_SYMBOL_GPL(v4l2_fwnode_connector_free);
> > > > > > > > > > +
> > > > > > > > > > +int v4l2_fwnode_connector_alloc_parse(struct fwnode_handle *fwnode,
> > > > > > > > > > +				      struct v4l2_fwnode_connector *connector)
> > > > > > > > > > +{
> > > > > > > > > > +	struct fwnode_handle *remote_pp, *remote_ep;
> > > > > > > > > > +	const char *type_name;
> > > > > > > > > > +	unsigned int i = 0, ep_num = 0;
> > > > > > > > > > +	int err;
> > > > > > > > > > +
> > > > > > > > > > +	memset(connector, 0, sizeof(*connector));
> > > > > > > > > > +
> > > > > > > > > > +	remote_pp = fwnode_graph_get_remote_port_parent(fwnode);
> > > > > > > > > 
> > > > > > > > > How do you know a remote endpoint is a connector, and not another device's
> > > > > > > > > endpoint?
> > > > > > > > 
> > > > > > > > Well, I think that the caller won't use this function if it isn't a
> > > > > > > > connector. If it helps I can check if the compatible of the remote ends
> > > > > > > > with "-connector".
> > > > > > > 
> > > > > > > The function is called by a driver. A driver shouldn't know what's at the
> > > > > > > other end of the graph arc; the information should come from the firmware
> > > > > > > instead.
> > > > > > > 
> > > > > > > On some board there could be another device where you have a connector now.
> > > > > > > 
> > > > > > > As the connector has its own compatible string, there could be a connector
> > > > > > > driver to tell this is actually a connector, even if there's nothing to
> > > > > > > control. It'd be a very tiny driver.
> > > > > > 
> > > > > > Yes I know a connector driver would be the best. This also have the
> > > > > > advantage to do drop the connector handling in each subdev driver.. But
> > > > > > unfortunately I haven't the time yet. Would it be okay for you too check
> > > > > > that the remote is a connector and if not to exit?
> > > > > 
> > > > > The current design is also problematic in the sense that it parses remote DT
> > > > > graph endpoints (as well as device nodes) that are not under the device's
> > > > > own scope.
> > > > 
> > > > You are right that is not good. Would it be okay with you to parse only
> > > > the local node so the caller must pass the connector node?
> > > > 
> > > > > I wonder what kind of changes would that require, and how much more
> > > > > difficult would the changes be to implement later on if a number of drivers
> > > > > uses the newly added APIs.
> > > > > 
> > > > > v4l2_fwnode_parse_endpoint() should be considered as well. This is the
> > > > > current API to parse endpoints. Could connectors be meaningfully parsed
> > > > > within v4l2_fwnode_parse_endpoint()?
> > > > 
> > > > I think v4l2_fwnode_endpoint_parse() isn't the correct place. Of course
> > > > it is a endpoint but I don't think that a connector should be placed
> > > > there. Currently the endpoint is mostly used to describe the connection
> > > > between the isp and a sensor. I think we shouldn't add something
> > > > unrelated just because it's an fw-endpoint. The connector just describes
> > > > who users can interact with the device. A connector isn't connected to a
> > > > chip using mipi or something else.
> > > 
> > > If the endpoints pointing to a connector are not parsed by
> > > v4l2_fwnode_endpoint_parse(), then it means that they're parsed somewhere
> > > else, and that's something the caller needs to know. The fact that there is
> > > a connector, is only apparent from the compatible string of the remote
> > > device. That's simply not something for the caller to figure out.
> > 
> > That is a goot point, I got that.
> > 
> > > Endpoints in general refer to other devices' connection points. It doesn't
> > > matter what kind of a device it is, they should be treated the same way.
> > > 
> > > I'm still not proposing to mangle connectors with the bus properties. Still,
> > > the two are mostly exclusive: if there's a connector, then any properties of
> > > the signal likely have nothing to do what was described in the firmware.
> > > 
> > > How about adding an fwnode API function called e.g.g
> > > v4l2_fwnode_is_connector(), to tell whether a given local endpoint is
> > > connected to a remote which is a connector? That, I think, would be
> > > sufficient to make the connectors vs. wired busses easy for drivers to work
> > > with.
> > 
> > A v4l2_fwnode_is_connector() function is nice. Just to got you right,
> > you want something like:
> > 
> > 	v4l2_fwnode_endpoint_alloc_parse()
> > 	{
> > 		int rval;
> > 
> > 		if (v4l2_fwnode_is_connector())
> > 			return v4l2_fwnode_connector_alloc_parse();
> > 
> > 		rval = __v4l2_fwnode_endpoint_parse(fwnode, vep);
> > 		if (rval < 0)
> > 			return rval;
> > 
> > 		...
> > 	}
> > 
> > If I got that right we need to squash the 'struct v4l2_fwnode_connector'
> > into the 'struct v4l2_fwnode_endpoint' or we need to accept both structs.
> > The first attempt can be error prone if a caller access invalid data.
> > What do you think?
> 
> After my short excursion to the drm subsystem I noticed such a function:
> drm_of_find_panel_or_bridge(). Basically the function fills a bridge or
> panel struct and the driver need to check if there was a panel or a
> bridge. It seems that we can use exactly the same logic for our
> use-case.

We could. Then the bus_type field would likely need to be used for the
connector types as well. The field would seem to deserve a rename as a
result though.

-- 
Sakari Ailus
sakari.ailus@linux.intel.com