linux-kernel - Re: staging: udlfb -- staging version does not work, external does

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Date:	Sun, 11 Apr 2010 19:18:56 +0200
From:	Pavel Machek <pavel@....cz>
To:	Bernie Thompson <bernie@...gable.com>
Cc:	roberto@...it.it, gregkh@...e.de, Cyril Hrubis <metan@....cz>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: staging: udlfb -- staging version does not work, external does

On Sun 2010-04-11 10:05:12, Bernie Thompson wrote:
> Roberto - why would any mmap'd writes get immediately displayed on the
> older code?  I wouldn't expect that.
> 
> I'm assuming this is mmio path, and that there's no triggers for
> repaint in the older code?
> 
> Pavel - the issue for mmio access is when to trigger repaint.

I'm not doing any memory mapped access (that's what mmio means,
right?). I even checked with strace -- cat uses plain old
read()/write() syscalls.

cat /bin/bash > /dev/fb1

(can you try it on your system? do we agree that it should fill cca
half of screen with noise?)

> Repainting the entire screen is extremely expensive, and mmio doesn't
> have any built-in trigger point.  This issue is what the whole defio
> circus (page-fault based trigger) has been about for the last few
> months.  Some history at:  http://plugable.com/category/project/udlfb/

Ok, I'll take a look.... ...

   Todo

(this should really go to udlfb/TODO).

  ...
     * Disable defio by default, unfortunately, because of several
bugs without obvious solutions
          * rendering problems with pages (lines) that no longer get
updated - writes to those are
            no longer triggering deferred processing
          * When running 2 USB adapters, dirty pages for one instance
seem to affect the other, and
            vice versa (udlfb has no common state, so appears to be in
defio or mmu handling)
          * cases where we hit a kernel oops in the deferred io
handler when it tries to touch the
            pages it's been asked to handle.
  ...

Aha, so this one is even known. How do I re-enable defio support, so
that it can be debugged?

And... can we do something stupid like full repaint once a second to
get basically working driver?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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