linux-kernel - Re: [PATCH 2/4 v4] i.MX31: Image Processing Unit DMA and IRQ drivers

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Message-ID: <20081223121300.GL9472@pengutronix.de>
Date:	Tue, 23 Dec 2008 13:13:00 +0100
From:	Robert Schwebel <r.schwebel@...gutronix.de>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net, adaplas@...il.com,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 2/4 v4] i.MX31: Image Processing Unit DMA and IRQ
	drivers

On Tue, Dec 23, 2008 at 11:50:06AM +0100, Sascha Hauer wrote:
> > You mean an output v4l device? I think overlays are handled by framebuffer 
> > drivers... But I'm also not quite sure about it, however, handling overlay 
> > as another framebuffer seems logical to me.
>
> Well the DMA engine seems to suggest that frames should be passed around
> whereas the framebuffer API only has a single frame. That would fit
> better into the v4l API. Also the IPU can do things like colourspace
> conversion and hw scaling which would fit into the V4L API.

Looks like a candidate for gstreamer on the userspace end. Can it be
decoupled enough to make proper plugins out of it?

> BTW is the overlay framebuffer useful in it's current implementation?
> There seems to be no way to adjust the x/y offset or the blending
> modes.

The API Eric Miao just posted for the PXA looks sane to me.

> > If there are no other problems with v5, could we maybe take it as a
> > basis and then I would submit a patch to reduce the number of IRQs?
>
> Please understand my concerns with this driver. It's a quite complex
> beast and experience shows that once a driver is in the kernel it is
> far more complicated to change it than to do it right the first way.

Especially when it comes to userspace visible things.

> You know that I'm also interested in having a MX31 framebuffer (and
> camera) driver in kernel but I want to make sure that it works
> properly and leaves room for feature enhancements without having to
> refactor the whole driver.

Yup, looks like it would be better to cook it another round instead of
trying to bring in a half-tested driver with brute-force.

rsc
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