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

[Chris Wilson <chris@chris-wilson.co.uk>]

On Mon, Oct 07, 2013 at 12:25:03PM +0300, Ville Syrjälä wrote:
> 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@linux.intel.com wrote:
> > > From: Ville Syrjälä <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]
> > > 
> > > 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?

No, appears I mislead you. The last one to successfully work was the
composite v1 patch set. Sorry.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre