From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Subject: Re: [PATCH 3/4] drm/i915: Enabling pre-multiplied alpha
 drm property
Date: Thu, 20 Mar 2014 15:29:42 +0530
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To: Damien Lespiau <damien.lespiau@intel.com>
Cc: David Airlie <airlied@linux.ie>, Daniel Vetter <daniel.vetter@ffwll.ch>, intel-gfx@lists.freedesktop.org, "Srinivas, Vidya" <vidya.srinivas@intel.com>
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Hi Damien,

On Wed, 2014-03-19 at 15:10 +0000, Damien Lespiau wrote:
> On Sat, Mar 08, 2014 at 01:51:18PM +0530, sagar.a.kamble@intel.com wrote:
> > From: Sagar Kamble <sagar.a.kamble@intel.com>
> > 
> > This patch enables property for changin the pixel format
> > of plane to enable/disable pre-multiplied alpha format.
> > Client has to set BIT(DRM_BLEND_PREMULTIPLIED_ALPHA) | 0x0/0x1
> > to disable/enable pre-multiplied alpha format.
> > 
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > Cc: David Airlie <airlied@linux.ie>
> > Signed-off-by: Srinivas, Vidya <vidya.srinivas@intel.com>
> > Signed-off-by: Sagar Kamble <sagar.a.kamble@intel.com>
> 
> Huum, the alpha being premultiplied or not seems to be a property of the
> framebuffer to me, not of the plane. It seems to me that we should
> define alternative premultiplied DRM_FORMATs and make the sprite planes
> advertise support for premultiplied fbs in the format list when the
> hardware indeed supports them.
This is what i think of usage of this property:

Composer/user mode starts using plane with XRGB format and then it wants
to add transparency to the plane. So it will set the format to ARGB
format and provide buffer for that plane that will have pixels with
pre-multiplied alpha (a*r, a*g, a*b, a).
This can be done with primary plane(CRTC) as well, however I have 
not added this as CRTC property since CRTCs are going to be drm_plane
soon.

Will this kind of interface for usermode to toggle the pixel format's
alpha be useful?

Thanks,
Sagar