linux-kernel - Re: [PATCH 09/10] MCDE: Add build files and bus

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Date:	Sun, 5 Dec 2010 12:28:14 +0100
From:	Daniel Vetter <daniel@...ll.ch>
To:	Alex Deucher <alexdeucher@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Jimmy RUBIN <jimmy.rubin@...ricsson.com>,
	Dan JOHANSSON <dan.johansson@...ricsson.com>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>,
	Marcus LORENTZON <marcus.xm.lorentzon@...ricsson.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [PATCH 09/10] MCDE: Add build files and bus

On Sat, Dec 04, 2010 at 04:34:22PM -0500, Alex Deucher wrote:
> This doesn't seem that different from the graphics chips we support
> with kms.  I don't think it would require much work to use KMS.  One
> thing we considered, but never ended up implementing was a generic
> overlay API for KMS.  Most PC hardware still has overlays, but we
> don't use them much any more on the desktop side.  It may be
> worthwhile to design an appropriate API for them for these type of
> hardware.

Just fyi about a generic overlay api: I've looked a bit into this when
doing the intel overlay support and I think adding special overlay crtcs
that can be attached real crtcs gives a nice clean api. We could the reuse
the existing framebuffer/pageflipping api to get the buffers to the
overlay engine.

The real pain starts when we want format discovery from userspace with all
the alignement/size/layout constrains. Add in tiling support and its
almost impossible to do in a generic way. But also for kms userspace needs
to know these constrains (implemented for generic use in libkms). I favor
such an approach for overlays, too (if it ever happens) - i.e. a few
helpers in libkms that allocate an appropriate buffer for a given format
and size and returns the buffer, strides and offsets for the different
planes.

-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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