linux-kernel - Re: [Intel-gfx] [PATCH] drm/intel: Only smash VGA SR01 register if intel is default VGA device

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Date:	Tue, 17 Dec 2013 10:17:24 -0800
From:	Keith Packard <keithp@...thp.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	intel-gfx@...ts.freedesktop.org,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/intel: Only smash VGA SR01 register if intel is default VGA device

Chris Wilson <chris@...is-wilson.co.uk> writes:

> The bspec still says we must assert SR01 bit5 prior to disabling the VGA
> plane.
>
> Perhaps the test should be whether (vga_reg & VGA_DISP_DISABLE) == 0 and
> do nothing if the plane is already off.

The problem is that for some reason we're smashing *some other video
card* when it's being used via efifb.

I'm wondering if vgaarb just doesn't work because efifb isn't telling
vgaarb that it's using those registers (I mean, how would it even know?)

The other simple option is to just not disable VGA if the card isn't
primary; presumably it wasn't ever enabled.

And, yes, I know that the card probably won't work at all if it isn't
primary because so much currently depends on the BIOS setting up bits of
the card that we can't autodetect. So, another simple option would be to
just refuse to load the driver if the card is secondary...

-- 
keith.packard@...el.com

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