linux-kernel - Re: [PATCH 1/5] video: move mediabus format definition to a more standard place

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Date:	Tue, 23 Sep 2014 18:09:23 +0200
From:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH 1/5] video: move mediabus format definition to a more
 standard place

Hi Guennadi,

On Tue, 23 Sep 2014 14:33:20 +0200 (CEST)
Guennadi Liakhovetski <g.liakhovetski@....de> wrote:

> Hi Boris,
> 
> On Tue, 22 Jul 2014, 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 macros that points to VIDEO_BUS_FMT_
> > definitions.
> > 
> > Signed-off-by: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> 
> In principle I find this a good idea, certainly it's good to reuse code. 
> Just wondering, wouldn't it be better instead of adding those defines to 
> define a macro like
> 
> #define VIDEO_BUS_TO_MBUS(x)	V4L2_MBUS_ ## x = VIDEO_BUS_ ## x
> 
> and then do
> 
> enum v4l2_mbus_pixelcode {
> 	VIDEO_BUS_TO_MBUS(FIXED),
> 	VIDEO_BUS_TO_MBUS(RGB444_2X8_PADHI_BE),
> 	...
> };
> 
> ? I'm not very strong on this, I just think an enum is nicer than a bunch 
> of defines and this way copy-paste errors are less likely, but if you or 
> others strongly disagree - I won't insist :)

I'd say it might be a good solution if we enforce new users (including
user space users) to use video_bus_format enum values instead of
v4l2_mbus_pixelcode ones. But if we keep adding new values to this enum
I'd say this approach is less readable than having the full names
(V4L2_MBUS_XXX) expressed, because users will still have to use those
full names.

Anyway, I can still replace this macro list by an enum:

enum v4l2_mbus_pixelcode {
	V4L2_MBUS_FIXED = VIDEO_BUS_FIXED,
	V4L2_MBUS_RGB444_2X8_PADHI_BE = VIDEO_BUS_RGB444_2X8_PADHI_BE,
	...
};

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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