Re: [PATCH libdrm] libdrm: update drm/drm_fourcc.h from kernel to add multi plane formats

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

Hello,

On 04/06/2012 11:22 AM, Kyungmin Park wrote:
> + V4L2 develper
> Sylwester, please give your opinions? How to handle it at v4l2 side.
> 
> Thank you,
> Kyungmin Park
> 
> On Apr 6, 2012 12:44 AM, "Ville Syrjälä" <syrjala@sci.fi
> <mailto:syrjala@sci.fi>> wrote:
> 
>     On Fri, Apr 06, 2012 at 03:05:36PM +0900, Inki Dae wrote:
>     > Hi Ville,
>     >
>     > > -----Original Message-----
>     > > From: Ville Syrjälä [mailto:ville.syrjala@linux.intel.com
>     <mailto:ville.syrjala@linux.intel.com>]
>     > > Sent: Friday, April 06, 2012 3:14 AM
>     > > To: airlied@redhat.com <mailto:airlied@redhat.com>
>     > > Cc: inki.dae@samsung.com <mailto:inki.dae@samsung.com>;
>     kyungmin.park@samsung.com <mailto:kyungmin.park@samsung.com>; dri-
>     > > devel@lists.freedesktop.org <mailto:devel@lists.freedesktop.org>;
>     Seung-Woo Kim
>     > > Subject: Re: [PATCH libdrm] libdrm: update drm/drm_fourcc.h from kernel to
>     > > add multi plane formats
>     > >
>     > > On Fri, Mar 30, 2012 at 01:12:58PM +0300, Ville Syrjälä wrote:
>     > > > On Fri, Mar 30, 2012 at 11:54:50AM +0900, Seung-Woo Kim wrote:
>     > > > > Multi buffer plane pixel formats are added as like kernel header.
>     > > > >
>     > > > > Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com
>     <mailto:sw0312.kim@samsung.com>>
>     > > > > ---
>     > > > >  include/drm/drm_fourcc.h |    7 +++++++
>     > > > >  1 files changed, 7 insertions(+), 0 deletions(-)
>     > > > >
>     > > > > diff --git a/include/drm/drm_fourcc.h b/include/drm/drm_fourcc.h
>     > > > > index 85facb0..7cfd95a 100644
>     > > > > --- a/include/drm/drm_fourcc.h
>     > > > > +++ b/include/drm/drm_fourcc.h
>     > > > > @@ -107,6 +107,10 @@
>     > > > >  #define DRM_FORMAT_NV16                fourcc_code('N', 'V', '1',
>     '6') /*
>     > > 2x1 subsampled Cr:Cb plane */
>     > > > >  #define DRM_FORMAT_NV61                fourcc_code('N', 'V', '6',
>     '1') /*
>     > > 2x1 subsampled Cb:Cr plane */
>     > > > >
>     > > > > +/* 2 non contiguous plane YCbCr */
>     > > > > +#define DRM_FORMAT_NV12M       fourcc_code('N', 'M', '1', '2') /* 2x2
>     > > subsampled Cr:Cb plane */
>     > > >
>     > > > NAK. DRM_FORMAT_NV12 handles this just fine.
>     > >
>     > > And I just realized that I was already too late with my NAK since this a
>     > > libdrm patch. Apparently the kernel drm_fourcc.h changes were snuck in
>     > > via some backdoor without review. Sigh.
>     > >
>     >
>     > We had already requested review for it. for this you can refer to link
>     > below:
>     >
>     > http://lists.freedesktop.org/archives/dri-devel/2011-December/017654.html
> 
>     I see. I couldn't find it in my work mailbox for some reason, and I
>     don't remember having seen the patch before. I suppose I just missed it
>     due to Christmas vacations, and was too blind to see it in my mailbox.
>     Also google decicded to filter my search results too much, so I didn't
>     spot it via the web archives either. I'm sorry for the false accusation.
> 
>     > > So they're now in Linus's tree. But looks like format_check() was never
>     > > updated to accept them, so there's no way anyone could actually be using
>     > > them. So Dave, can we still remove them from the kernel header?
>     > >
>     >
>     > Yes, right. these formats aren't used for any SoCs except Exynos series yet
>     > but just we are first. I think they should be added because anyone may use
>     > them someday at least possible.
> 
>     Since DRM_FORMAT_NV12M is _identical_ to DRM_FORMAT_NV12, I see no point
>     in adding it (similarly for YUV420M vs. YUV420).

In V4L2 the fourcc also determines the number of memory planes in the frame
buffer. The multi-planar API has been added to support devices with odd
alignment requirements (image components, like Y/CbCr in separate physical
memory buffers) for which it was difficult to map whole frame into contiguous
user memory region.

Here is some excample:
http://linuxtv.org/downloads/v4l-dvb-apis/V4L2-PIX-FMT-NV12M.html

I'm not terribly familiar with the buffer structure in DRM, maybe there are
better ways to handle something like this in DRI.

>     --
>     Ville Syrjälä
>     syrjala@sci.fi <mailto:syrjala@sci.fi>
>     http://www.sci.fi/~syrjala/

Regards,
-- 
Sylwester Nawrocki
Samsung Poland R&D Center