linux-kernel - Re: [git pull] drm: previous pull req + 1.

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Date:	Tue, 23 Jun 2009 11:58:44 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Hellström <thomas@...pmail.org>,
	Dave Airlie <airlied@...ux.ie>,
	Alex Deucher <alexdeucher@...il.com>,
	Andrew Lutomirski <luto@....edu>, dri-devel@...ts.sf.net,
	Jerome Glisse <jglisse@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [git pull] drm: previous pull req + 1.

On Mon, 2009-06-22 at 18:18 -0700, Jesse Barnes wrote:
> I think it could work, but ideally we'd keep the kernel fbcon object
> pinned, and keep printing into it even while some other gfx app is
> running.  That way we don't have to dump the whole queue into it when
> a
> panic occurs, we can just switch buffers (something like this would
> also be handy for dual head debugging; one head running your desktop
> and the other a debug console printing all the messages).  That's
> slightly more invasive surgery though...  I should have a chance to do
> something like that as part of the kdb/kms work I'll be doing with
> Jason.
> 
Do we really need that ?

We can easily repaint (ie, regenerate the fb content from the pseudo
vgacon image kept by the console layer).

So if we want the kernel to "take" over, it's reasonably easy to
make it also repaint the content of the fb.

How, of course, kicking out usespace with unmap_mapping_ranges() isn't
going to work well from an oops or something at interrupt time, we
do need to have a reasonably safe path for these things, which is why
I believe that sort of emergency printing should be done without
any acceleration, just basic manual painting in the front buffer...

Should we even bother changing the mode ? Not sure...

Cheers,
Ben.

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