Re: [PATCH v6 02/17] media: v4l2: async: Allow searching for asd of any type

[Steve Longerbeam]

Hi Mauro, Sakari,


On 09/26/2018 03:40 AM, Sakari Ailus wrote:
> Hi Mauro, Steve,
>
> On Wed, Sep 26, 2018 at 06:33:35AM -0300, Mauro Carvalho Chehab wrote:
> > Em Tue, 25 Sep 2018 18:05:36 -0700
> > Steve Longerbeam <steve_longerbeam@xxxxxxxxxx> escreveu:
> >
> > > On 09/25/2018 03:20 PM, Mauro Carvalho Chehab wrote:
> > > > Em Tue, 25 Sep 2018 14:04:21 -0700
> > > > Steve Longerbeam <steve_longerbeam@xxxxxxxxxx> escreveu:
> > > >   
> > > > > >      
> > > > > > > @@ -392,12 +406,11 @@ static int __v4l2_async_notifier_register(struct v4l2_async_notifier *notifier)
> > > > > > >     		case V4L2_ASYNC_MATCH_CUSTOM:
> > > > > > >     		case V4L2_ASYNC_MATCH_DEVNAME:
> > > > > > >     		case V4L2_ASYNC_MATCH_I2C:
> > > > > > > -			break;
> > > > > > >     		case V4L2_ASYNC_MATCH_FWNODE:
> > > > > > > -			if (v4l2_async_notifier_fwnode_has_async_subdev(
> > > > > > > -				    notifier, asd->match.fwnode, i)) {
> > > > > > > +			if (v4l2_async_notifier_has_async_subdev(
> > > > > > > +				    notifier, asd, i)) {
> > > > > > >     				dev_err(dev,
> > > > > > > -					"fwnode has already been registered or in notifier's subdev list\n");
> > > > > > > +					"asd has already been registered or in notifier's subdev list\n");
> > > > > > Please, never use "asd" on messages printed to the user. While someone
> > > > > > may understand it while reading the source code, for a poor use,
> > > > > > "asd" is just a random sequence of 3 characters.
> > > > > I will change the message to read:
> > > > >
> > > > > "subdev descriptor already listed in this or other notifiers".
> > > > Perfect!
> > > But the error message is removed in the subsequent patch
> > > "[PATCH 03/17] media: v4l2: async: Add v4l2_async_notifier_add_subdev".
> > >
> > > I could bring it back as a dev_dbg() in v4l2_async_notifier_asd_valid(), but
> > > this shouldn't be a dev_err() anymore since it is up to the media platform
> > > to decide whether an already existing subdev descriptor is an error.
> > Hmm... that's an interesting discussion... what cases do you think it
> > would be fine to try to register twice an asd notifier?

It should be a fairly common case that a sub-device has multiple fwnode
output ports. In that case it's possible multiple sub-devices downstream
from it will each encounter it when parsing the fwnode graph, and attempt
to add it to their notifiers asd_list multiple times. That isn't an 
error, any
attempt to add it after the first add should be ignored.

imx-media is an example, there is a CSI-2 transmitter with four fwnode
output ports for each CSI-2 virtual channel. Those channels each go to
one of four Camera Sensor Interface in the imx6 IPU. So each CSI will
encounter the CSI-2 transmitter when parsing its fwnode ports.


> Only the error message is removed; this case is still considered an error.
> I think it'd be better to keep this error message; it helps debugging.

Ok I will add it back, but it should be a dev_dbg().

Steve

> > Haven't write myself any piece of code using async framework, on a first
> > glance, trying to register twice sounds like an error to me.
> >
> > Sakari, what do you think?