Em Tue, 25 Aug 2015 09:28:55 +0200
Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:
> On 08/23/2015 10:17 PM, Mauro Carvalho Chehab wrote:
> > By adding an union at media_link, we get for free a way to
> > represent interface->entity links.
> >
> > No need to change anything at the code, just at the internal
> > header file.
> >
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>
> >
> > diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> > index 17bb5cbbd67d..f6e8fa801cf9 100644
> > --- a/include/media/media-entity.h
> > +++ b/include/media/media-entity.h
> > @@ -75,14 +75,20 @@ struct media_pipeline {
> > struct media_link {
> > struct media_gobj graph_obj;
> > struct list_head list;
> > - struct media_pad *source; /* Source pad */
> > - struct media_pad *sink; /* Sink pad */
> > + union {
> > + struct media_gobj *port0;
> > + struct media_pad *source;
> > + };
> > + union {
> > + struct media_gobj *port1;
> > + struct media_pad *sink;
> > + };
> > struct media_link *reverse; /* Link in the reverse direction */
> > unsigned long flags; /* Link flags (MEDIA_LNK_FL_*) */
> > };
> >
> > struct media_pad {
> > - struct media_gobj graph_obj;
> > + struct media_gobj graph_obj; /* should be the first object */
> > struct media_entity *entity; /* Entity this pad belongs to */
> > u16 index; /* Pad index in the entity pads array */
> > unsigned long flags; /* Pad flags (MEDIA_PAD_FL_*) */
> > @@ -105,7 +111,7 @@ struct media_entity_operations {
> > };
> >
> > struct media_entity {
> > - struct media_gobj graph_obj;
> > + struct media_gobj graph_obj; /* should be the first object */
>
> Does adding these "/* should be the first object */" comments in media_entity
> and media_pad belong to this patch? It doesn't seem to be related to the union
> change.
It is related. See:
union {
struct media_gobj *port0;
struct media_pad *source;
};
If we keep the graph_obj as the first part of media_pad, the pad
object can be accessed as either:
link->port0
or
link->source->graph_obj.
In practice, it means that, if one wants to know the type of the
object, it could do:
type = media_type(link->port0)
Technically, we don't need yet to put the comment at the media_entity,
as the patch that will create interface->entity links is patch 20.
But I opted to do the comments change altogether.
>
> I would also suggest that "/* must be first field in struct */" is a better
> phrase.
OK.
>
> Regards,
>
> Hans
>
> > struct list_head list;
> > const char *name; /* Entity name */
> > u32 type; /* Entity type (MEDIA_ENT_T_*) */
> > @@ -119,7 +125,7 @@ struct media_entity {
> > u16 num_backlinks; /* Number of backlinks */
> >
> > struct media_pad *pads; /* Pads array (num_pads objects) */
> > - struct list_head links; /* Links list */
> > + struct list_head links; /* Pad-to-pad links list */
> >
> > const struct media_entity_operations *ops; /* Entity operations */
> >
> >
>
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