Re: [PATCH] media: v4l2-async: Accept endpoints and devices for fwnode matching

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

On Wed, Mar 18, 2020 at 09:52:25AM +0200, Sakari Ailus wrote:
> On Wed, Mar 18, 2020 at 02:17:26AM +0200, Laurent Pinchart wrote:
> > On Wed, Mar 18, 2020 at 01:04:32AM +0200, Laurent Pinchart wrote:
> >> On Tue, Mar 17, 2020 at 02:44:56PM +0200, Sakari Ailus wrote:
> >>> On Sun, Mar 15, 2020 at 02:55:11PM +0200, Laurent Pinchart wrote:
> >>>> fwnode matching was designed to match on nodes corresponding to a
> >>>> device. Some drivers, however, needed to match on endpoints, and have
> >>>> passed endpoint fwnodes to v4l2-async. This works when both the subdev
> >>>> and the notifier use the same fwnode types (endpoint or device), but
> >>>> makes drivers that use different types incompatible.
> >>>> 
> >>>> Fix this by extending the fwnode match to handle fwnodes of different
> >>>> types. When the types (deduced from the node name) are different,
> >>>> retrieve the device fwnode for the side that provides an endpoint
> >>>> fwnode, and compare it with the device fwnode provided by the other
> >>>> side. This allows interoperability between all drivers, regardless of
> >>>> which type of fwnode they use for matching.
> >>>> 
> >>>> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> >>>> ---
> >>>> This has been compile-tested only. Prabhakar, could you check if it
> >>>> fixes your issue ?
> >>>> 
> >>>>  drivers/media/v4l2-core/v4l2-async.c | 42 +++++++++++++++++++++++++++-
> >>>>  1 file changed, 41 insertions(+), 1 deletion(-)
> >>>> 
> >>>> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> >>>> index 8bde33c21ce4..995e5464cba7 100644
> >>>> --- a/drivers/media/v4l2-core/v4l2-async.c
> >>>> +++ b/drivers/media/v4l2-core/v4l2-async.c
> >>>> @@ -71,7 +71,47 @@ static bool match_devname(struct v4l2_subdev *sd,
> >>>>  
> >>>>  static bool match_fwnode(struct v4l2_subdev *sd, struct v4l2_async_subdev *asd)
> >>>>  {
> >>>> -	return sd->fwnode == asd->match.fwnode;
> >>>> +	struct fwnode_handle *other_fwnode;
> >>>> +	struct fwnode_handle *dev_fwnode;
> >>>> +	bool asd_fwnode_is_ep;
> >>>> +	bool sd_fwnode_is_ep;
> >>>> +	const char *name;
> >>>> +
> >>>> +	/*
> >>>> +	 * Both the subdev and the async subdev can provide either an endpoint
> >>>> +	 * fwnode or a device fwnode. Start with the simple case of direct
> >>>> +	 * fwnode matching.
> >>>> +	 */
> >>>> +	if (sd->fwnode == asd->match.fwnode)
> >>>> +		return true;
> >>>> +
> >>>> +	/*
> >>>> +	 * Otherwise, check if the sd fwnode and the asd fwnode refer to an
> >>>> +	 * endpoint or a device. If they're of the same type, there's no match.
> >>>> +	 */
> >>>> +	name = fwnode_get_name(sd->fwnode);
> >>>> +	sd_fwnode_is_ep = name && strstarts(name, "endpoint");
> >>>> +	name = fwnode_get_name(asd->match.fwnode);
> >>>> +	asd_fwnode_is_ep = name && strstarts(name, "endpoint");
> >>> 
> >>> Apart from the fact that you're parsing graph node names here, this looks
> >>> good.
> > 
> > And why is that an issue btw ? the ACPI fwnode ops seem to provide a
> > .get_name() operation, would it return the ACPI bus ID here ?
> 
> I'd really prefer not to do graph parsing outside the main parser(s), OF,
> ACPI and property frameworks.
> 
> Just for an example, the v4l2_fwnode_link_parse() was broken for ACPI for a
> long time just because it did not use the graph parsing functions, but
> implemented graph parsing on its own.
> 
> >>> How about checking instead that calling
> >>> fwnode_graph_get_remote_endpoint(fwnode_graph_get_remote_endpoint()) yields
> >>> the same node? That would ensure you're dealing with endpoint nodes without
> >>> explicitly parsing the graph in any way.
> >> 
> >> Would it be simpler to check for the presence of an endpoint property ?
> 
> There's no endpoint property, apart from an old ACPI definition.

There isn't ? How does it work on ACPI then ?
acpi_graph_get_remote_endpoint() starts with

	ret = acpi_node_get_property_reference(__fwnode, "remote-endpoint", 0,
					       &args);

> There are differences in the implementations and this is not the best place
> to try to take them all into account.

OK, but in that case I think we need an fwnode_graph_is_endpoint().

-- 
Regards,

Laurent Pinchart