linux-kernel - Re: [PATCHv2] ISP:BUILD:FIX: Move media_entity

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Message-Id: <201108241525.47332.laurent.pinchart@ideasonboard.com>
Date:	Wed, 24 Aug 2011 15:25:46 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	"Hiremath, Vaibhav" <hvaibhav@...com>
Cc:	"Ravi, Deepthy" <deepthy.ravi@...com>,
	"mchehab@...radead.org" <mchehab@...radead.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCHv2] ISP:BUILD:FIX: Move media_entity_init() and

Hi Vaibhav,

On Wednesday 24 August 2011 14:19:01 Hiremath, Vaibhav wrote:
> On Wednesday, August 24, 2011 5:00 PM Laurent Pinchart wrote: 
> > On Wednesday 24 August 2011 13:21:27 Ravi, Deepthy wrote:
> > > On Wed, Aug 24, 2011 at 4:47 PM, Laurent Pinchart wrote:
> > > > On Friday 19 August 2011 15:48:45 Deepthy Ravi wrote:
> > > >> From: Vaibhav Hiremath <hvaibhav@...com>
> > > >> 
> > > >> Fix the build break caused when CONFIG_MEDIA_CONTROLLER
> > > >> option is disabled and if any sensor driver has to be used
> > > >> between MC and non MC framework compatible devices.
> > > >> 
> > > >> For example,if tvp514x video decoder driver migrated to
> > > >> MC framework is being built without CONFIG_MEDIA_CONTROLLER
> > > >> option enabled, the following error messages will result.
> > > >> drivers/built-in.o: In function `tvp514x_remove':
> > > >> drivers/media/video/tvp514x.c:1285: undefined reference to
> > > >> `media_entity_cleanup'
> > > >> drivers/built-in.o: In function `tvp514x_probe':
> > > >> drivers/media/video/tvp514x.c:1237: undefined reference to
> > > >> `media_entity_init'
> > > > 
> > > > If the tvp514x is migrated to the MC framework, its Kconfig option
> > > > should depend on MEDIA_CONTROLLER.
> > > 
> > > The same TVP514x driver is being used for both MC and non MC compatible
> > > devices, for example OMAP3 and AM35x. So if it is made dependent on
> > > MEDIA CONTROLLER, we cannot enable the driver for MC independent
> > > devices.
> > 
> > Then you should use conditional compilation in the tvp514x driver itself.
> > Or
> 
> No. I am not in favor of conditional compilation in driver code.

Actually, thinking some more about this, you should make the tvp514x driver 
depend on CONFIG_MEDIA_CONTROLLER unconditionally. This doesn't mean that the 
driver will become unusable by applications that are not MC-aware. 
Hosts/bridges don't have to export subdev nodes, they can just call subdev 
pad-level operations internally and let applications control the whole device 
through a single V4L2 video node.

> > better, port the AM35x driver to the MC API.
> 
> Why should we use MC if I have very simple device (like AM35x) which only
> supports single path? I can very well use simple V4L2 sub-dev based
> approach (master - slave), isn't it?

The AM35x driver should use the in-kernel MC and V4L2 subdev APIs, but it 
doesn't have to expose them to userspace.

-- 
Regards,

Laurent Pinchart
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