linux-kernel - Re: [PATCH 2/3] fbdev: Make deferred I/O work as advertized

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Date:	Thu, 20 Mar 2008 06:55:11 +0800
From:	"Jaya Kumar" <jayakumar.lkml@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	armbru@...hat.com, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	linux-fbdev-devel@...ts.sourceforge.net, adaplas@....net,
	linux-input@...r.kernel.org, dmitry.torokhov@...il.com
Subject: Re: [PATCH 2/3] fbdev: Make deferred I/O work as advertized

On Thu, Mar 20, 2008 at 6:39 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
>  Well all we have in the changelog is
>
>   Implement support for the E-Ink Metronome controller.  It provides an
>   mmapable interface to the controller using defio support.  It was tested
>   with a gumstix pxa255 with Vizplex media using Xfbdev and various X
>   clients such as xeyes, xpdf, xloadimage.
>
>  grump.  This say nothing at all about the change to drivers/video/fb_defio.c.

I apologize. I should have done better.

>
>  a) the changelog _should_ document this change.  Please send a paragraph and
>    I'll add it.

This patch fixes the following bug. Defio would cause a hang on write
access to the framebuffer as the page fault would be called
ad-infinitum. It fixes fb_defio by setting the mapping to be used by
page_mkclean.

>
>  b) If this discussion hadn't happened, that bug (whatever it is) would
>    have remained unfixed in 2.6.25.  As a direct consequence of poor
>    changelogging.

Understood. The root cause of my flaw was my assumption that other
than me, there weren't any users of defio so I was in no hurry to get
it fixed.

>
>  c) This bugfix (whatever it is) should have been in a separate patch.

Understood. It won't happen again.

Thanks,
jaya
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