linux-kernel - Re: [PATCH 01/15] [media] Move mediabus format definition to a more standard place

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Date:	Tue, 04 Nov 2014 12:09:59 +0100
From:	Hans Verkuil <hansverk@...co.com>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
CC:	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-api@...r.kernel.org, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: [PATCH 01/15] [media] Move mediabus format definition to a more
 standard place

Well, I gave two alternatives :-)

Both are fine as far as I am concerned, but it would be nice to hear
what others think.

Regards,

	Hans

On 11/04/14 11:45, Boris Brezillon wrote:
> Hi Hans,
> 
> On Tue, 04 Nov 2014 11:20:40 +0100
> Hans Verkuil <hansverk@...co.com> wrote:
> 
>> Hi Boris,
>>
>> On 11/04/14 10:54, Boris Brezillon wrote:
>>> Rename mediabus formats and move the enum into a separate header file so
>>> that it can be used by DRM/KMS subsystem without any reference to the V4L2
>>> subsystem.
>>>
>>> Old V4L2_MBUS_FMT_ definitions are now referencing MEDIA_BUS_FMT_ value.
>>
>> I missed earlier that v4l2-mediabus.h contained a struct as well, so it can't be
>> deprecated and neither can a #warning be added.
>>
>> The best approach, I think, is to use a macro in media-bus-format.h
>> that will either define just the MEDIA_BUS value when compiled in the kernel, or
>> define both MEDIA_BUS and V4L2_MBUS values when compiled for userspace.
>>
>> E.g. something like this:
>>
>> #ifdef __KERNEL__
>> #define MEDIA_BUS_FMT_ENTRY(name, val) MEDIA_BUS_FMT_ # name = val
>> #else
>> /* Keep V4L2_MBUS_FMT for backwards compatibility */
>> #define MEDIA_BUS_FMT_ENTRY(name, val) \
>> 	MEDIA_BUS_FMT_ # name = val, \
>> 	V4L2_MBUS_FMT_ # name = val
>> #endif
> 
> Okay, but this means we keep adding V4L2_MBUS_FMT_ definitions even for
> new formats (which definitely doesn't encourage people to move on).
> Moreover, we add a V4L2 prefix in what was supposed to be a subsystem
> neutral header.
> 
> Anyway, these are just nitpicks, and if you prefer this approach
> I'll rework my series :-).
> 
>>
>> An alternative approach is to have v4l2-mediabus.h include media-bus-format.h,
>> put #ifndef __KERNEL__ around the enum v4l2_mbus_pixelcode and add a big comment
>> there that applications should use the defines from media-bus-format.h and that
>> this enum is frozen (i.e. new values are only added to media-bus-format.h).
>>
>> But I think I like the macro idea best.
> 
> As you wish, my only intent is to use those bus format definitions in a
> DRM driver :-).
> 
> Thanks,
> 
> Boris
> 
> 
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