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

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Date:	Tue, 23 Jun 2009 11:04:39 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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 17:24 -0700, Linus Torvalds wrote:
> 
> On Tue, 23 Jun 2009, Benjamin Herrenschmidt wrote:
> > 
> > As far as I can remember, all fbdev operations are done under the
> > console semaphore.
> 
> Yeah, and some of them are horribly broken (ie copying data from user 
> space while doing it - causing horrible things like VC switching latencies 
> and invisible printk's if an oops happens during the op).
> 
> Or maybe that got fixed. 

Well, it does rely on userspace behaving.. ie, no accel ops are done by
the kernel in KD_GRAPHICS and userspace is -supposed- to switch to
KD_GRAPHICS before touching the fb.

In fact, nowdays, we do have the infrastructure to be smart and enforce
that. IE. Instead of using a boring remap_page_ranges() in fb_mmap() we
could use a fault handler. When in KD_TEXT, we fail them, when in
KD_GRAPHICS, we service them, and we unmap_mapping_range() when
switching. Something like that...

Dunno how that interacts with the new DRM thingy though.

Cheers,
Ben.

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