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

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Message-ID: <20081223125612.GB17159@pengutronix.de>
Date:	Tue, 23 Dec 2008 13:56:12 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Robert Schwebel <r.schwebel@...gutronix.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 01:45:14PM +0100, Guennadi Liakhovetski wrote:
> Hi Robert,
> 
> On Tue, 23 Dec 2008, Robert Schwebel wrote:
> 
> > 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?
> 
> I think, the question is rather "can a driver be written for IPU to 
> support some sane hardware-neutral image data manipulation API, like v4l?" 
> Then you can start writing any user-space apps on top of that API. So, as 
> long as there is such an API, I think, we can put it on IPU, yes. My 
> problems ATM is - no use-case. What concerns overlay, it is not used in 
> the current application, as for image format conversion from the camera - 
> I only have a Bayer camera to test with. I even cannot test monochrome 
> sanely, because of a lack of a cable:-) And Bayer and monochrome don't 
> make good candidates for such conversions - they are not supported by the 
> IPU.
> 
> > > 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.
> 
> I'll have a look, but as I said: -ENOUSER:-)
> 
> > > > 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.
> 
> Ok, no problem. Let's just decide
> 
> 1. is the drivers/dma the final location.
> 2. do dmaengine maintainers accept it in present form or require any 
>    amendments.
> 3. which interrupts we make visible by default for irq_desc[] and what 
>    granularity we want to enable the rest (we could even just make 
>    CONFIG_ALL_IPU_IRQS and be 95% sure noone will ever need them.)
> 4. throw away every trace of overlay support - if anyone ever needs it 
>    they should be able to dig it out in ML archives.

Or from the Freescale BSP. This sounds good to me. It would also enable
someone to write a v4l2 based overlay driver without interfering with
the existing framebuffer driver.

Sascha

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