From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [PATCH v2 1/1] drm/i915: Fix VGA handling using
 stop_machine() or mmio
Date: Mon, 30 Sep 2013 15:24:37 +0100
Message-ID: <20130930142437.GI744@nuc-i3427.alporthouse.com>
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On Mon, Sep 30, 2013 at 05:08:31PM +0300, ville.syrjala@linux.intel.com wro=
te:
> From: Ville Syrj=E4l=E4 <ville.syrjala@linux.intel.com>
> =

> We have several problems with out VGA handling:
> - We try to use the GMCH control VGA disable bit even though it may
>   be locked
> - If we manage to disable VGA throuh GMCH control, we're no longer
>   able to correctly disable the VGA plane
> - Taking part in the VGA arbitration is too expensive for X [1]

I'd like to emphasize that X disables DRI if it detects 2 vga cards,
effectively breaking all machines with a discrete GPU. Even if one of
those is not being used.
 =

> +/*
> + * 21 devices with 8 functions per device max on the same bus.
> + * We don't need locking for these due to stop_machine().
> + */
> +static u16 vga_cmd[21*8];
> +static u16 vga_ctl[21*8];

Should we just allocate storage for when we need it? We are now adding
several hundred bytes to our module, which is bound to cause us to use
an extra page, and they can be passed around through the stop_machine
closure rather than static.

But anyway, it does what is says on the tin and makes my dGPU testing
box usable again, without breaking any other machine that I've tested on
so far,
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris

-- =

Chris Wilson, Intel Open Source Technology Centre