Hi Geert,
Thanks for your feedback.
On 2017-07-18 09:11:19 +0200, Geert Uytterhoeven wrote:
> Hi Niklas,
>
> On Mon, Jul 17, 2017 at 6:59 PM, Niklas Söderlund
> <niklas.soderlund+rene...@ragnatech.se> wrote:
> > Add a subdevice specific notifier which can be used by a subdevice
> > driver to compliment the master device notifier to extend the subdevice
> > discovery.
> >
> > The master device registers the subdevices closest to itself in its
> > notifier while the subdevice(s) register notifiers for their closest
> > neighboring devices. Subdevice drivers configures a notifier at probe
> > time which are registered by the v4l2-async framework once the subdevice
> > itself is register, since it's only at this point the v4l2_dev is
> > available to the subnotifier.
> >
> > Using this incremental approach two problems can be solved:
> >
> > 1. The master device no longer has to care how many devices exist in
> > the pipeline. It only needs to care about its closest subdevice and
> > arbitrary long pipelines can be created without having to adapt the
> > master device for each case.
> >
> > 2. Subdevices which are represented as a single DT node but register
> > more than one subdevice can use this to improve the pipeline
> > discovery, since the subdevice driver is the only one who knows which
> > of its subdevices is linked with which subdevice of a neighboring DT
> > node.
> >
> > To allow subdevices to provide its own list of subdevices to the
> > v4l2-async framework v4l2_async_subdev_register_notifier() is added.
> > This new function must be called before the subdevice itself is
> > registered with the v4l2-async framework using
> > v4l2_async_register_subdev().
> >
> > Signed-off-by: Niklas Söderlund <niklas.soderlund+rene...@ragnatech.se>
>
> Thanks for your patch!
>
> > --- a/drivers/media/v4l2-core/v4l2-async.c
> > +++ b/drivers/media/v4l2-core/v4l2-async.c
>
> > @@ -217,6 +293,12 @@ void v4l2_async_notifier_unregister(struct
> > v4l2_async_notifier *notifier)
> > "Failed to allocate device cache!\n");
> > }
> >
> > + subdev = kvmalloc_array(n_subdev, sizeof(*subdev), GFP_KERNEL);
> > + if (!dev) {
>
> if (!subdev) {
Wops, copy-past coding strikes again! Will fix.
>
> (noticed accidentally[*] :-)
>
> > + dev_err(notifier->v4l2_dev->dev,
> > + "Failed to allocate subdevice cache!\n");
> > + }
> > +
> > mutex_lock(&list_lock);
> >
> > list_del(¬ifier->list);
> > @@ -224,6 +306,8 @@ void v4l2_async_notifier_unregister(struct
> > v4l2_async_notifier *notifier)
> > list_for_each_entry_safe(sd, tmp, ¬ifier->done, async_list) {
> > if (dev)
> > dev[count] = get_device(sd->dev);
> > + if (subdev)
> > + subdev[count] = sd;
>
> I don't like these "memory allocation fails, let's continue but check the
> pointer first"-games.
> Why not abort when the dev/subdev arrays cannot be allocated? It's not
> like the system is in a good state anyway.
> kmalloc() may have printed a big fat warning and invoked the OOM-killer
> already.
I agree, and I also don't like these "games". In my first attempt to
work with this function I did remove the memory game, but then it hit me
that if I did I would alter behavior of the function and I did not dare
to do so.
Hopefully this can be addressed in the future if someone ever gets
around to reworking the whole mess of re-probing devices which IMOH
looks a but like a hack :-) I also ofc be happy to just remove the
memory game from this function and as you suggest simply abort if the
allocation fails, but I feel I need the blessing from the v4l2 community
before doing so. Sometimes v4l2 do funny stuff for legacy reasons beyond
my understanding.
>
> [*] while checking if you perhaps removed the "dev" games in a later patch.
> No, you added another one :-(
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> ge...@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like
> that.
> -- Linus Torvalds
--
Regards,
Niklas Söderlund
