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Subject: Re: [Linux-fbdev-devel] [PATCH 2.6.20 1/1] fbdev, mm: hecuba/E-Ink
	fbdev driver
From: "Antonino A. Daplas" <adaplas@gmail.com>
To: linux-fbdev-devel@lists.sourceforge.net
Cc: Paul Mundt <lethal@linux-sh.org>, Jaya Kumar <jayakumar.lkml@gmail.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, Geert.Uytterhoeven@sonycom.com,
       jsimmons@infradead.org
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Date: Thu, 22 Feb 2007 07:43:33 +0800
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On Mon, 2007-02-19 at 23:13 -0500, Jaya Kumar wrote: 
> On 2/18/07, Paul Mundt <lethal@linux-sh.org> wrote:
> > Given that, this would have to be something that's dealt with at the
> > subsystem level rather than in individual drivers, hence the desire to
> > see something like this more generically visible.
> >
> 
> Hi Peter, Paul, fbdev folk,
> 
> Ok. Here's what I'm thinking for abstracting this:
> 
> fbdev drivers would setup fb_mmap with their own_mmap as usual. In
> own_mmap, they would do what they normally do and setup a vm_ops. They
> are free to have their own nopage handler but would set the
> page_mkwrite handler to be fbdev_deferred_io_mkwrite().
> fbdev_deferred_io_mkwrite would build up the list of touched pages and
> pass it to a delayed workqueue which would then mkclean on each page

Yes, this functionality is sorely needed by more than a few driver
writers.

> and then pass a copy of that page list down to a driver's callback
> function. The fbdev driver's callback function can then do the actual
> IO to the framebuffer or coalesce DMA based on the provided page list.
> I would like to add something like the following to struct fb_info:
> 
> #ifdef CONFIG_FB_DEFERRED_IO
> struct fb_deferred_io *defio;
> #endif
> 
> to store the mutex (to protect the page list), the touched page list,
> and the driver's callback function.
> 
> I hope this sounds sufficiently generic to meet everyone's (the two of
> us? :) needs.

There's definitely more than two :-).  For the past several years,
various people have been asking for this functionality.  So yes,
implementing this in a generic manner will be a big help.

Tony

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