Hi Daniel,
On Fri, Jun 17, 2022 at 11:33:03PM +0100, Daniel Scally wrote:
> On 17/06/2022 22:34, Daniel Scally wrote:
> > On 14/06/2022 20:11, Paul Elder wrote:
> >> From: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> >>
> >> The media_entity_remote_pad() helper function returns the first remote
> >> pad it find connected to a given pad. Beside being possibly ill-named
> >> (as it operates on a pad, not an entity) and non-deterministic (as it
> >> stops at the first enabled link), the fact that it returns the first
> >> match makes it unsuitable for drivers that need to guarantee that a
> >> single link is enabled, for instance when an entity can process data
> >> from one of multiple sources at a time.
> >>
> >> For those use cases, add a new helper function,
> >> media_entity_remote_pad_unique(), that operates on an entity and returns
> >> a remote pad, with a guarantee that only one link is enabled. To ease
> >> its use in drivers, also add an inline wrapper that locates source pads
> >> specifically. A wrapper that locates sink pads can easily be added when
> >> needed.
> >>
> >> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> >> ---
> >> Documentation/driver-api/media/mc-core.rst | 4 +-
> >> drivers/media/mc/mc-entity.c | 38 ++++++++++++++++++
> >> include/media/media-entity.h | 45 ++++++++++++++++++++++
> >> 3 files changed, 85 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/Documentation/driver-api/media/mc-core.rst b/Documentation/driver-api/media/mc-core.rst
> >> index 02481a2513b9..a2d1e32e3abb 100644
> >> --- a/Documentation/driver-api/media/mc-core.rst
> >> +++ b/Documentation/driver-api/media/mc-core.rst
> >> @@ -186,8 +186,8 @@ is required and the graph structure can be freed normally.
> >>
> >> Helper functions can be used to find a link between two given pads, or a pad
> >> connected to another pad through an enabled link
> >> -:c:func:`media_entity_find_link()` and
> >> -:c:func:`media_entity_remote_pad()`.
> >> +(:c:func:`media_entity_find_link()`, :c:func:`media_entity_remote_pad()` and
> >> +:c:func:`media_entity_remote_source_pad()`).
> >>
> >> Use count and power handling
> >> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> diff --git a/drivers/media/mc/mc-entity.c b/drivers/media/mc/mc-entity.c
> >> index 11f5207f73aa..1febf5a86be6 100644
> >> --- a/drivers/media/mc/mc-entity.c
> >> +++ b/drivers/media/mc/mc-entity.c
> >> @@ -9,6 +9,7 @@
> >> */
> >>
> >> #include <linux/bitmap.h>
> >> +#include <linux/list.h>
> >> #include <linux/property.h>
> >> #include <linux/slab.h>
> >> #include <media/media-entity.h>
> >> @@ -920,6 +921,43 @@ struct media_pad *media_entity_remote_pad(const struct media_pad *pad)
> >> }
> >> EXPORT_SYMBOL_GPL(media_entity_remote_pad);
> >>
> >> +struct media_pad *
> >> +media_entity_remote_pad_unique(const struct media_entity *entity,
> >> + unsigned int type)
> >> +{
> >> + struct media_pad *pad = NULL;
> >> + struct media_link *link;
> >> +
> >> + list_for_each_entry(link, &entity->links, list) {
> >> + struct media_pad *local_pad;
> >> + struct media_pad *remote_pad;
> >> +
> >> + if (!(link->flags & MEDIA_LNK_FL_ENABLED))
> >> + continue;
> >
> > Does this need another guard here to make sure the link isn't an
> > ancillary link? Only likely to happen at least in the immediate future
> > where the entity represents a camera sensor, so possibly not applicable
> > here - I couldn't find where the new function is used in the series to
> > check. I _think_ it would actually work ok regardless...media_gobj
> > type-punning makes my brain ache, but I think the local_pad->entity ==
> > entity comparison would actually compare the entity->name member of the
> > entity at the end of an ancillary link to the entity parameter, not find
> > a match and so continue the loop without failing, but that feels a bit
> > sub-optimal.
>
> Or perhaps a better approach would be to provide something like a
> "list_for_each_data_link()" iterator - the potential problem here (as
> with Quentin's recent issue with the rkisp1 driver) is the assumption
> that all links are data links, so maybe it's best to just guarantee that
> if we can.
I agree with you, without a dedicated iterator, we're bound to repeat
the mistake over and over.
Would you like to submit a patch to add that iterator, or should I ? I'd
name it for_each_media_entity_data_link() or something similar.
> >> +
> >> + if (type == MEDIA_PAD_FL_SOURCE) {
> >> + local_pad = link->sink;
> >> + remote_pad = link->source;
> >> + } else {
> >> + local_pad = link->source;
> >> + remote_pad = link->sink;
> >> + }
> >> +
> >> + if (local_pad->entity == entity) {
> >> + if (pad)
> >> + return ERR_PTR(-ENOTUNIQ);
> >> +
> >> + pad = remote_pad;
> >> + }
> >> + }
> >> +
> >> + if (!pad)
> >> + return ERR_PTR(-ENOLINK);
> >> +
> >> + return pad;
> >> +}
> >> +EXPORT_SYMBOL_GPL(media_entity_remote_pad_unique);
> >> +
> >> static void media_interface_init(struct media_device *mdev,
> >> struct media_interface *intf,
> >> u32 gobj_type,
> >> diff --git a/include/media/media-entity.h b/include/media/media-entity.h
> >> index a9a1c0ec5d1c..33d5f52719a0 100644
> >> --- a/include/media/media-entity.h
> >> +++ b/include/media/media-entity.h
> >> @@ -859,6 +859,51 @@ struct media_link *media_entity_find_link(struct media_pad *source,
> >> */
> >> struct media_pad *media_entity_remote_pad(const struct media_pad *pad);
> >>
> >> +/**
> >> + * media_entity_remote_pad_unique - Find a remote pad connected to an entity
> >> + * @entity: The entity
> >> + * @type: The type of pad to find (MEDIA_PAD_FL_SINK or MEDIA_PAD_FL_SOURCE)
> >> + *
> >> + * Search for and return a remote pad of @type connected to @entity through an
> >> + * enabled link. If multiple (or no) remote pads match these criteria, an error
> >> + * is returned.
> >> + *
> >> + * The uniqueness constraint makes this helper function suitable for entities
> >> + * that support a single active source or sink at a time.
> >> + *
> >> + * Return: A pointer to the remote pad, or one of the following error pointers
> >> + * if an error occurs:
> >> + *
> >> + * * -ENOTUNIQ - Multiple links are enabled
> >> + * * -ENOLINK - No connected pad found
> >> + */
> >> +struct media_pad *
> >> +media_entity_remote_pad_unique(const struct media_entity *entity,
> >> + unsigned int type);
> >> +
> >> +/**
> >> + * media_entity_remote_source_pad - Find a remote source pad connected to an entity
> >> + * @entity: The entity
> >> + *
> >> + * Search for and return a remote source pad connected to @entity through an
> >> + * enabled link. If multiple (or no) remote pads match these criteria, an error
> >> + * is returned.
> >> + *
> >> + * The uniqueness constraint makes this helper function suitable for entities
> >> + * that support a single active source at a time.
> >> + *
> >> + * Return: A pointer to the remote pad, or one of the following error pointers
> >> + * if an error occurs:
> >> + *
> >> + * * -ENOTUNIQ - Multiple links are enabled
> >> + * * -ENOLINK - No connected pad found
> >> + */
> >> +static inline struct media_pad *
> >> +media_entity_remote_source_pad(const struct media_entity *entity)
> >> +{
> >> + return media_entity_remote_pad_unique(entity, MEDIA_PAD_FL_SOURCE);
> >> +}
> >> +
> >> /**
> >> * media_entity_is_streaming - Test if an entity is part of a streaming pipeline
> >> * @entity: The entity
--
Regards,
Laurent Pinchart
