Re: [PATCH v2 3/4] media: v4l2-async: Log message in case of heterogenous fwnode match

[Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>]

Hi Laurent,

On 18/03/2020 00:25, Laurent Pinchart wrote:
> When a notifier supplies a device fwnode and a subdev supplies an
> endpoint fwnode, incorrect matches may occur if multiple subdevs
> correspond to the same device fwnode. This can't be handled
> transparently in the framework, and requires the notifier to switch to
> endpoint fwnodes. Log a message to notify of this problem. A second
> message is added to help accelerating the transition to endpoint
> matching.

Only minor comments and discussion below:

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/media/v4l2-core/v4l2-async.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> index 224b39a7aeb1..9f393a7be455 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/drivers/media/v4l2-core/v4l2-async.c
> @@ -77,6 +77,7 @@ static bool match_fwnode(struct v4l2_async_notifier *notifier,
>  	struct fwnode_handle *dev_fwnode;
>  	bool asd_fwnode_is_ep;
>  	bool sd_fwnode_is_ep;
> +	struct device *dev;
>  	const char *name;
>  
>  	/*
> @@ -113,7 +114,28 @@ static bool match_fwnode(struct v4l2_async_notifier *notifier,
>  
>  	fwnode_handle_put(dev_fwnode);
>  
> -	return dev_fwnode == other_fwnode;
> +	if (dev_fwnode != other_fwnode)
> +		return false;
> +
> +	/*
> +	 * We have an heterogenous match. Retrieve the struct device of the

s/an/a/

s/heterogenous/heterogeneous/ (and that's not an en-gb/en-us thing)
Also in $SUBJECT

> +	 * side that matched on a device fwnode to print its driver name.
> +	 */
> +	if (sd_fwnode_is_ep)
> +		dev = notifier->v4l2_dev ? notifier->v4l2_dev->dev
> +		    : notifier->sd->dev;

Eugh ... I guess if this gets needed elsewhere, notifiers need a helper
to get the appropriate dev out... but if this is the only place, then so
be it.


> +	else
> +		dev = sd->dev;
> +
> +	if (dev && dev->driver) {
> +		if (sd_fwnode_is_ep)
> +			dev_info(dev, "Driver %s uses device fwnode, incorrect match may occur\n",
> +				 dev->driver->name);
> +		dev_info(dev, "Consider updating driver %s to match on endpoints\n",
> +			 dev->driver->name);

I think I interpret that in the case that existing drivers match on
dev->dev (i.e. no endpoints involved) then this will not print, as we
would already have matched and returned earlier in the function.

I don't think that's a problem, but it means people will not be
'encouraged' to move to endpoint matching until they encounter a device
which uses endpoints.

Perhaps that's ok ... but I was almost thinking of being more 'pushy'
and guiding device matches to move to endpoints too ;-)


> +	}
> +
> +	return true;
>  }
>  
>  static bool match_custom(struct v4l2_async_notifier *notifier,
>