From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from lb1-smtp-cloud6.xs4all.net ([194.109.24.24]:49980 "EHLO lb1-smtp-cloud6.xs4all.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755427AbcCWO5S (ORCPT ); Wed, 23 Mar 2016 10:57:18 -0400 Subject: Re: [PATCH v5 1/2] media: Add obj_type field to struct media_entity To: Laurent Pinchart References: <1458722756-7269-1-git-send-email-laurent.pinchart+renesas@ideasonboard.com> <20160323073552.18db3b7e@recife.lan> <56F2A2B5.80206@xs4all.nl> <3511467.97gkNM9KCE@avalon> Cc: Mauro Carvalho Chehab , Laurent Pinchart , linux-media@vger.kernel.org, Sakari Ailus From: Hans Verkuil Message-ID: <56F2AEC6.4030209@xs4all.nl> Date: Wed, 23 Mar 2016 15:57:10 +0100 MIME-Version: 1.0 In-Reply-To: <3511467.97gkNM9KCE@avalon> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 03/23/2016 03:45 PM, Laurent Pinchart wrote: > Hi Hans, > > On Wednesday 23 Mar 2016 15:05:41 Hans Verkuil wrote: >> On 03/23/2016 11:35 AM, Mauro Carvalho Chehab wrote: >>> Em Wed, 23 Mar 2016 10:45:55 +0200 Laurent Pinchart escreveu: >>>> Code that processes media entities can require knowledge of the >>>> structure type that embeds a particular media entity instance in order >>>> to cast the entity to the proper object type. This needs is shown by the >>>> presence of the is_media_entity_v4l2_io and is_media_entity_v4l2_subdev >>>> functions. >>>> >>>> The implementation of those two functions relies on the entity function >>>> field, which is both a wrong and an inefficient design, without even >>>> mentioning the maintenance issue involved in updating the functions >>>> every time a new entity function is added. Fix this by adding add an >>>> obj_type field to the media entity structure to carry the information. >>>> >>>> Signed-off-by: Laurent Pinchart >>>> >>>> Acked-by: Hans Verkuil >>>> Acked-by: Sakari Ailus >>>> --- >>>> >>>> drivers/media/media-device.c | 2 + >>>> drivers/media/v4l2-core/v4l2-dev.c | 1 + >>>> drivers/media/v4l2-core/v4l2-subdev.c | 1 + >>>> include/media/media-entity.h | 79 ++++++++++++++++------------- >>>> 4 files changed, 46 insertions(+), 37 deletions(-) >>>> >>>> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c >>>> index 4a97d92a7e7d..88d8de3b7a4f 100644 >>>> --- a/drivers/media/media-device.c >>>> +++ b/drivers/media/media-device.c >>>> @@ -580,6 +580,8 @@ int __must_check media_device_register_entity(struct >>>> media_device *mdev, >>>> "Entity type for entity %s was not initialized!\n", >>>> entity->name); >>>> >>>> + WARN_ON(entity->obj_type == MEDIA_ENTITY_TYPE_INVALID); >>>> + >>> >>> This is not ok. There are valid cases where the entity is not embedded >>> on some other struct. That's the case of connectors/connections, for >>> example: a connector/connection entity doesn't need anything else but >>> struct media device. >> >> Once connectors are enabled, then we do need a MEDIA_ENTITY_TYPE_CONNECTOR >> or MEDIA_ENTITY_TYPE_STANDALONE or something along those lines. > > MEDIA_ENTITY_TYPE_CONNECTOR would make sense, but only if we add a struct > media_connector. I believe that can be a good idea, at least to simplify > management of the entity and the connector pad(s). > >>> Also, this is V4L2 specific. Neither ALSA nor DVB need to use >>> container_of(). Actually, this won't even work there, as the entity is >>> stored as a pointer, and not as an embedded data. > > That's sounds like a strange design decision at the very least. There can be > valid cases that require creation of bare entities, but I don't think they > should be that common. > >> Any other subsystem that *does* embed this can use obj_type. If it doesn't >> embed it in anything, then MEDIA_ENTITY_TYPE_STANDALONE should be used (or >> whatever name we give it). I agree that we need a type define for the case >> where it is not embedded. > > I'd like to point out that I had defined MEDIA_ENTITY_TYPE_MEDIA_ENTITY for > that purpose in v4, and was requested to drop it. I think MEDIA_ENTITY_TYPE_MEDIA_ENTITY is very ugly. Hm, some alternatives: MEDIA_ENTITY_TYPE_NONE MEDIA_ENTITY_TYPE_ME MEDIA_ENTITY_TYPE_SINGLETON MEDIA_ENTITY_TYPE_BASE I personally prefer the last since it is just the media_entity base class by itself. Regards, Hans