Re: [PATCH 1/5] v4l2-subdev: Provide a port mapping for asynchronous subdevs

[Sakari Ailus]

Hi Kieran,

On Thu, Apr 27, 2017 at 11:13:50PM +0100, Kieran Bingham wrote:
> Hi Sakari,
> 
> Thanks for taking a look

Sure! :-)

> 
> On 27/04/17 22:43, Sakari Ailus wrote:
> > Hi Kieran,
> > 
> > Could I ask you to rebase your patches on top of my V4L2 fwnode patches
> > here?
> > 
> > <URL:https://git.linuxtv.org/sailus/media_tree.git/log/?h=v4l2-acpi>
> > 
> > It depends on the fwnode graph patches, merged here:
> > 
> > <URL:https://git.linuxtv.org/sailus/media_tree.git/log/?h=v4l2-acpi-merge>
> > 
> > I expect the fwnode graph patches in v4.12 so we'll have them in media-tree
> > master soon.
> > 
> > (I'm pushing these branches right now, it may take a while until it's really
> > there.)
> 
> Sure, I'll merge those into my base.
> 
> > On Thu, Apr 27, 2017 at 07:26:00PM +0100, Kieran Bingham wrote:
> >> From: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx>
> >>
> >> Devices such as the the ADV748x support multiple parallel stream routes
> >> through a single chip. This leads towards needing to provide multiple
> >> distinct entities and subdevs from a single device-tree node.
> >>
> >> To distinguish these separate outputs, the device-tree binding must
> >> specify each endpoint link with a unique (to the device) non-zero port
> >> number.
> >>
> >> This number allows async subdev registrations to identify the correct
> >> subdevice to bind and link.
> >>
> >> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx>
> >> ---
> >>  drivers/media/v4l2-core/v4l2-async.c  | 7 +++++++
> >>  drivers/media/v4l2-core/v4l2-subdev.c | 1 +
> >>  include/media/v4l2-async.h            | 1 +
> >>  include/media/v4l2-subdev.h           | 2 ++
> >>  4 files changed, 11 insertions(+)
> >>
> >> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> >> index 1815e54e8a38..875e6ce646ec 100644
> >> --- a/drivers/media/v4l2-core/v4l2-async.c
> >> +++ b/drivers/media/v4l2-core/v4l2-async.c
> >> @@ -42,6 +42,13 @@ static bool match_devname(struct v4l2_subdev *sd,
> >>  
> >>  static bool match_of(struct v4l2_subdev *sd, struct v4l2_async_subdev *asd)
> >>  {
> >> +	/*
> >> +	 * If set, we must match the device tree port, with the subdev port.
> >> +	 * This is a fast match, so do this first
> >> +	 */
> >> +	if (sd->port && sd->port != asd->match.of.port)
> > 
> > Zero is an entirely valid value for a port. I think it'd be good not to
> > depend on non-zero port values for port matching.
> 
> Well then that pretty much dashes my chances on not parsing the DT in the ADV
> driver.

Hmm. I guess there's no really a way to avoid it. But we could make it
easier 

> 
> 
> 
> >> +		return -1;
> > 
> > Any particular reason to return -1 from a function with bool return type?
> 
> Ahem, I clearly can't read ;-)
> I think my mindset was thinking strcmp or something...

But -1 is perfectly valid. If you wanted to make it look really interesting,
you could return -!false and still have exactly the same functionality. ;-)

> 
> 
> >> +
> >>  	return !of_node_cmp(of_node_full_name(sd->of_node),
> >>  			    of_node_full_name(asd->match.of.node));
> >>  }
> >> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> >> index da78497ae5ed..67f816f90ac3 100644
> >> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> >> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> >> @@ -607,6 +607,7 @@ void v4l2_subdev_init(struct v4l2_subdev *sd, const struct v4l2_subdev_ops *ops)
> >>  	sd->flags = 0;
> >>  	sd->name[0] = '\0';
> >>  	sd->grp_id = 0;
> >> +	sd->port = 0;
> >>  	sd->dev_priv = NULL;
> >>  	sd->host_priv = NULL;
> >>  #if defined(CONFIG_MEDIA_CONTROLLER)
> >> diff --git a/include/media/v4l2-async.h b/include/media/v4l2-async.h
> >> index 5b501309b6a7..2988960613ec 100644
> >> --- a/include/media/v4l2-async.h
> >> +++ b/include/media/v4l2-async.h
> >> @@ -56,6 +56,7 @@ struct v4l2_async_subdev {
> >>  	union {
> >>  		struct {
> >>  			const struct device_node *node;
> >> +			u32 port;
> > 
> > What if instead of storing the device's OF node, you'd store the port node
> > and used that for matching?
> > 
> > Would that also solve the problem or do I miss something?
> 
> Actually - I was 'trying' to prevent having to parse the DT in the adv748x
> driver if I didn't need to.
> 
> Once I have to parse the DT, then yes, I think storing the endpoint node is
> probably the best thing to compare against.
> 
> And actually - you might have just solved my open question in the cover letter ...
> 
> I had got stuck in my mindset that if I were to use the endpoint 'leaf' node as
> a comparator - that it would be 'instead' of the root node.
> 
> But actually - it could just be root-node + leaf-node to compare, which then
> allows us the fallback of comparing just the root nodes if the leaf isn't set.
> 
> I'll respin with this either tomorrow or early next week.

Endpoints are indeed another option.

Is there something that would prevent switching from device node matching to
port / endpoint matching altogether? I don't think the driver changes should
be difficult to make.

Supporting different options there will be painful as it will likely require
help from the driver to implement both --- separately.

> 
> > 
> >>  		} of;
> >>  		struct {
> >>  			const char *name;
> >> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> >> index 0ab1c5df6fac..1c1731b491e5 100644
> >> --- a/include/media/v4l2-subdev.h
> >> +++ b/include/media/v4l2-subdev.h
> >> @@ -782,6 +782,7 @@ struct v4l2_subdev_platform_data {
> >>   * @ctrl_handler: The control handler of this subdev. May be NULL.
> >>   * @name: Name of the sub-device. Please notice that the name must be unique.
> >>   * @grp_id: can be used to group similar subdevs. Value is driver-specific
> >> + * @port: driver-specific value to bind multiple subdevs with a single DT node.
> >>   * @dev_priv: pointer to private data
> >>   * @host_priv: pointer to private data used by the device where the subdev
> >>   *	is attached.
> >> @@ -814,6 +815,7 @@ struct v4l2_subdev {
> >>  	struct v4l2_ctrl_handler *ctrl_handler;
> >>  	char name[V4L2_SUBDEV_NAME_SIZE];
> >>  	u32 grp_id;
> >> +	u32 port;
> >>  	void *dev_priv;
> >>  	void *host_priv;
> >>  	struct video_device *devnode;
> > 

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@xxxxxx	XMPP: sailus@xxxxxxxxxxxxxx