[RFC 1/1] v4l: async: Add some debug prints

[Laurent Pinchart]

Hi Sakari,

On Wed, Feb 15, 2023 at 02:00:46PM +0200, Sakari Ailus wrote:
> On Fri, Feb 10, 2023 at 12:34:01AM +0200, Laurent Pinchart wrote:
> > Thank you for the patch.
> 
> Thanks for the review!
> 
> This was indeed hastily written, to help debugging a particular issue. But
> I hope it'll be useful for other purposes, too. V4L2 async is about to get
> more complicated soon.

Could it get simpler instead ? :-) Maybe one day v4l2-async may cross
the threshold of how much pain I can bear, and I'll rewrite it...

> > On Fri, Feb 10, 2023 at 12:16:34AM +0200, Sakari Ailus wrote:
> > > Just add some debug prints for V4L2 async sub-device matching process. These
> > > might come useful in figuring out why things don't work as expected.
> > > 
> > > Signed-off-by: Sakari Ailus <sakari.ailus at linux.intel.com>
> > > ---
> > > Frieder,
> > > 
> > > Can you try this? It prints what is being matched with what. Perhaps this
> > > could be merged in a bit more refined form if it proves useful.
> > > 
> > > Not tested in any way.
> > > 
> > >  drivers/media/v4l2-core/v4l2-async.c | 41 ++++++++++++++++++++++++----
> > >  1 file changed, 36 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> > > index 2f1b718a9189..6c13a9488415 100644
> > > --- a/drivers/media/v4l2-core/v4l2-async.c
> > > +++ b/drivers/media/v4l2-core/v4l2-async.c
> > > @@ -86,13 +86,18 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
> > >  	bool sd_fwnode_is_ep;
> > >  	struct device *dev;
> > >  
> > > +	dev_dbg(sd->dev, "async fwnode match %pfw vs. %pfw\n", sd_fwnode,
> > > +		asd->match.fwnode);
> > 
> > Let's be more explicit:
> > 
> > 	dev_dbg(sd->dev, "async fwnode match: need %pfw, trying %pfw\n",
> > 		sd_fwnode, asd->match.fwnode);
> > 
> > (feel free to adjust, as long as we differentiate what we're looking for
> > from what we're testing)
> 
> Yes.
> 
> > > +
> > >  	/*
> > >  	 * 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)
> > > +	if (sd_fwnode == asd->match.fwnode) {
> > > +		dev_dbg(sd->dev, "true\n");
> > 
> > 		dev_dbg(sd->dev, "direct match found\n");
> > 
> > >  		return true;
> > > +	}
> > >  
> > >  	/*
> > >  	 * Otherwise, check if the sd fwnode and the asd fwnode refer to an
> > > @@ -105,8 +110,12 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
> > >  	sd_fwnode_is_ep = fwnode_graph_is_endpoint(sd_fwnode);
> > >  	asd_fwnode_is_ep = fwnode_graph_is_endpoint(asd->match.fwnode);
> > >  
> > > -	if (sd_fwnode_is_ep == asd_fwnode_is_ep)
> > > +	dev_dbg(sd->dev, "async fwnode match %pfw vs. %pfw\n", sd_fwnode,
> > > +		asd->match.fwnode);
> > 
> > You've already printed this above, no need to repeat it.
> > 
> > > +	if (sd_fwnode_is_ep == asd_fwnode_is_ep) {
> > > +		dev_dbg(sd->dev, "unmatching node types (false)\n");
> > 
> > 		dev_dbg(sd->dev, "direct match not found\n");
> > 
> > >  		return false;
> > > +	}
> > >  
> > >  	/*
> > >  	 * The sd and asd fwnodes are of different types. Get the device fwnode
> > > @@ -120,10 +129,15 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
> > >  		other_fwnode = sd_fwnode;
> > >  	}
> > >  
> > > +	dev_dbg(sd->dev, "async fwnode (compat) match %pfw vs. %pfw\n",
> > > +		dev_fwnode, other_fwnode);
> > 
> > Same comment as above regarding "vs." not telling which is which.
> > 
> > > +
> > >  	fwnode_handle_put(dev_fwnode);
> > >  
> > > -	if (dev_fwnode != other_fwnode)
> > > +	if (dev_fwnode != other_fwnode) {
> > > +		dev_dbg(sd->dev, "false\n");
> > 
> > 		dev_dbg(sd->dev, "compat match not found\n");
> > 
> > >  		return false;
> > > +	}
> > >  
> > >  	/*
> > >  	 * We have a heterogeneous match. Retrieve the struct device of the side
> > > @@ -143,6 +157,8 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
> > >  			   dev->driver->name);
> > >  	}
> > >  
> > > +	dev_dbg(sd->dev, "true\n");
> > 
> > 	dev_dbg(sd->dev, "compat match found\n");
> > 
> > > +
> > >  	return true;
> > >  }
> > >  
> > > @@ -255,7 +271,10 @@ v4l2_async_nf_can_complete(struct v4l2_async_notifier *notifier)
> > >  			v4l2_async_find_subdev_notifier(sd);
> > >  
> > >  		if (subdev_notifier &&
> > > -		    !v4l2_async_nf_can_complete(subdev_notifier))
> > > +		    !v4l2_async_nf_can_complete(subdev_notifier)) {
> > > +			if (subdev_notifier->sd)
> > > +				deb_dbg(subdev_notifier->sd->dev,
> > > +					"cannot complete\n");
> > 
> > I'd add a reference to v4l2-async, either directly in the string, or
> > with a "%s: ", __func__ prefix. Otherwise the message will be easy to
> > miss. Same in other messages. Maybe a "v4l2-async: " prefix for all
> > debug messages ?
> 
> How about just "async: " for all of these? It's shorther, still unique, and
> these lines will be long.

"async" is a bit vague, I think you should mention V4L2 too. If this
ends up printing

3-0010 async: cannot complete

someone may wonder what it relates to. We're talking about debugging
messages here, let's make sure they improve debugging as much as
possible.

> > >  			return false;
> > >  	}
> > >  
> > > @@ -273,18 +292,27 @@ v4l2_async_nf_try_complete(struct v4l2_async_notifier *notifier)
> > >  	if (!list_empty(&notifier->waiting))
> > >  		return 0;
> > >  
> > > +	if (notifier->sd)
> > > +		deb_dbg(notifier->sd->dev, "trying to complete\n");
> > > +
> > >  	/* Check the entire notifier tree; find the root notifier first. */
> > >  	while (notifier->parent)
> > >  		notifier = notifier->parent;
> > >  
> > >  	/* This is root if it has v4l2_dev. */
> > > -	if (!notifier->v4l2_dev)
> > > +	if (!notifier->v4l2_dev) {
> > > +		if (notifier->sd)
> > > +			deb_dbg(notifier->sd->dev,
> > > +				"V4L2 device not available\n");
> > >  		return 0;
> > > +	}
> > >  
> > >  	/* Is everything ready? */
> > >  	if (!v4l2_async_nf_can_complete(notifier))
> > >  		return 0;
> > >  
> > > +	deb_dbg(notifier->sd->dev, "complete\n");
> > 
> > You guard against notifier->sd being NULL above, but not here. At least
> > one of the two is wrong.
> 
> I'll add a helper function to get the device safely.
> 
> > > +
> > >  	return v4l2_async_nf_call_complete(notifier);
> > >  }
> > >  
> > > @@ -386,6 +414,9 @@ v4l2_async_nf_try_all_subdevs(struct v4l2_async_notifier *notifier)
> > >  			continue;
> > >  
> > >  		ret = v4l2_async_match_notify(notifier, v4l2_dev, sd, asd);
> > > +		deb_dbg(sd->dev, "bound to %s's notifier (ret %d)\n",
> > > +			notifier->sd ? dev_name(notifier->sd->dev) : "no-dev",
> > > +			ret);
> > >  		if (ret < 0)
> > >  			return ret;
> > >  

-- 
Regards,

Laurent Pinchart