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

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Date:	Tue, 23 Jun 2009 08:39:44 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Michel Dänzer <michel@...nzer.net>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas@...line-mail2.netline.ch, Dave Airlie <airlied@...ux.ie>,
	Andrew Lutomirski <luto@....edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jerome Glisse <jglisse@...hat.com>, dri-devel@...ts.sf.net,
	Alex Deucher <alexdeucher@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [git pull] drm: previous pull req + 1.

On Tue, 23 Jun 2009 09:48:00 +0200
Michel Dänzer <michel@...nzer.net> wrote:
> > > 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.
> > 
> > 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.
> 
> It doesn't need to be pinned for that, does it? I think in the long
> run it's a bad idea to have it pinned all the time, think of machines
> with only 8 MB of VRAM...

Yeah, in the general case we shouldn't have to pin it...

> > (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).
> 
> On a side note, I did precisely that about ten years ago on my
> Amiga. :) Granted, that was using two separate framebuffer devices (X
> glint driver on top of pm2fb, debug messages on amifb), but I think
> even that case isn't possible ATM. I agree it would be nice, though
> realistically there's hardly a way around a second machine for
> graphics driver development anyway.

Oh I know, most operating systems have reasonable debugging facilities,
and have had for a long time.  Linux is the one lagging here.

I agree it probably won't be that helpful for low level gfx debugging,
but I'm trying to think beyond that too. :)

-- 
Jesse Barnes, Intel Open Source Technology Center
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