linux-kernel - Re: [RFC PATCH 06/20] lib: Add video format information library

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Date:   Thu, 21 Mar 2019 09:20:41 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-media@...r.kernel.org
Subject: Re: [RFC PATCH 06/20] lib: Add video format information library

Hi Boris,

On Wed, Mar 20, 2019 at 02:39:44PM +0100, Boris Brezillon wrote:
> On Tue, 19 Mar 2019 22:57:11 +0100
> Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> > Move the DRM formats API to turn this into a more generic image formats API
> > to be able to leverage it into some other places of the kernel, such as
> > v4l2 drivers.
> >
> > Signed-off-by: Maxime Ripard <maxime.ripard@...tlin.com>
> > ---
> >  include/linux/image-formats.h | 240 +++++++++++-
> >  lib/Kconfig                   |   7 +-
> >  lib/Makefile                  |   3 +-
> >  lib/image-formats-selftests.c | 326 +++++++++++++++-
> >  lib/image-formats.c           | 760 +++++++++++++++++++++++++++++++++++-
> >  5 files changed, 1336 insertions(+)
> >  create mode 100644 include/linux/image-formats.h
> >  create mode 100644 lib/image-formats-selftests.c
> >  create mode 100644 lib/image-formats.c
> >
>
> [...]
>
> > --- /dev/null
> > +++ b/lib/image-formats.c
> > @@ -0,0 +1,760 @@
> > +#include <linux/bug.h>
> > +#include <linux/image-formats.h>
> > +#include <linux/kernel.h>
> > +#include <linux/math64.h>
> > +
> > +#include <uapi/drm/drm_fourcc.h>
> > +
> > +static const struct image_format_info formats[] = {
> > +	{
>
> ...
>
> > +	},
> > +};
> > +
> > +#define __image_format_lookup(_field, _fmt)			\
> > +	({							\
> > +		const struct image_format_info *format = NULL;	\
> > +		unsigned i;					\
> > +								\
> > +		for (i = 0; i < ARRAY_SIZE(formats); i++)	\
> > +			if (formats[i]._field == _fmt)		\
> > +				format = &formats[i];		\
> > +								\
> > +		format;						\
> > +	})
> > +
> > +/**
> > + * __image_format_drm_lookup - query information for a given format
> > + * @drm: DRM fourcc pixel format (DRM_FORMAT_*)
> > + *
> > + * The caller should only pass a supported pixel format to this function.
> > + *
> > + * Returns:
> > + * The instance of struct image_format_info that describes the pixel format, or
> > + * NULL if the format is unsupported.
> > + */
> > +const struct image_format_info *__image_format_drm_lookup(u32 drm)
> > +{
> > +	return __image_format_lookup(drm_fmt, drm);
> > +}
> > +EXPORT_SYMBOL(__image_format_drm_lookup);
> > +
> > +/**
> > + * image_format_drm_lookup - query information for a given format
> > + * @drm: DRM fourcc pixel format (DRM_FORMAT_*)
> > + *
> > + * The caller should only pass a supported pixel format to this function.
> > + * Unsupported pixel formats will generate a warning in the kernel log.
> > + *
> > + * Returns:
> > + * The instance of struct image_format_info that describes the pixel format, or
> > + * NULL if the format is unsupported.
> > + */
> > +const struct image_format_info *image_format_drm_lookup(u32 drm)
> > +{
> > +	const struct image_format_info *format;
> > +
> > +	format = __image_format_drm_lookup(drm);
> > +
> > +	WARN_ON(!format);
> > +	return format;
> > +}
> > +EXPORT_SYMBOL(image_format_drm_lookup);
>
> I think this function and the DRM formats table should be moved in
> drivers/gpu/drm/drm_image_format.c since they are DRM specific. The
> remaining functions can IMHO be placed in include/linux/image-formats.h
> as static inline funcs. This way you can get rid of lib/image-formats.c
> and the associated Kconfig entry.

I'm not quite sure what you mean. The whole point of the series is to
split out that table out of DRM so that we can use it in other places,
so surely putting it back into DRM defeats the purpose?

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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