[Intel-gfx] [PATCH v3] drm/i915: Fix VGA handling using stop_machine() or mmio

Ville Syrjälä ville.syrjala at linux.intel.com
Mon Oct 7 11:25:03 CEST 2013

On Mon, Oct 07, 2013 at 10:15:16AM +0100, Chris Wilson wrote:
> On Wed, Oct 02, 2013 at 04:42:55PM +0300, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at 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]
> > 
> > So let's treat the GMCH control VGA disable bit as read-only and leave
> > it for the BIOS to set, as it was intended. To disable VGA we will use
> > the VGA misc register, and to disable VGA IO we will disable IO space
> > completely via the PCI command register.
> > 
> > But we still need VGA register access during resume (and possibly during
> > lid event on insane BIOSen) to disable the VGA plane. Also we need to
> > re-disable VGA memory decode via the VGA misc register on resume.
> > 
> > Luckily up to gen4, VGA registers can be accessed through MMIO.
> > Unfortunately from gen5 onwards only the legacy VGA IO port range
> > works. So on gen5+ we still need IO space to be enabled during those
> > few special moments when we need to access VGA registers.
> > 
> > We still want to opt out of VGA arbitration on gen5+, so we have keep
> > IO space disabled most of the time. And when we do need to poke at VGA
> > registers, we enable IO space briefly while no one is looking. To
> > guarantee that no one is looking we will use stop_machine().
> > 
> > [1] http://lists.x.org/archives/xorg-devel/2013-September/037763.html
> > 
> > v2: Use SNB_GMCH_TRL on SNB+
> >     Use port IO instead of MMIO on CTG/ELK
> >     Add WaEnableVGAAccessThroughIOPort comment
> >     Fix the max number of devices on the bus limit
> > v3: Allocate the temp space dynamically
> >     Print some errors if we fail to execute the vga "op" due to alloc failure
> Passes the dGPU test, the SNB laptop, but is doa for CTG.

Crap. And v2 still works all right there?

Ville Syrjälä
Intel OTC

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