Re: [Intel-gfx] [PATCH 1/2] drm/i915: Extend the async flip VT-d w/a to skl/bxt

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Oct 04, 2021 at 10:50:00AM -0700, Matt Roper wrote:
> On Sat, Oct 02, 2021 at 01:01:31AM +0300, Ville Syrjälä wrote:
> > On Fri, Oct 01, 2021 at 02:08:15PM -0700, Matt Roper wrote:
> > > On Thu, Sep 30, 2021 at 10:09:42PM +0300, Ville Syrjala wrote:
> > > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > 
> > > > Looks like skl/bxt/derivatives also need the plane stride
> > > > stretch w/a when using async flips and VT-d is enabled, or
> > > > else we get corruption on screen. To my surprise this was
> > > > even documented in bspec, but only as a note on the
> > > > CHICHKEN_PIPESL register description rather than on the
> > > > w/a list.
> > > > 
> > > > So very much the same thing as on HSW/BDW, except the bits
> > > > moved yet again.
> > > 
> > > Bspec 7522 doesn't say anything about this requirement being tied to
> > > VT-d on these platforms.  Should we drop the intel_vtd_active()
> > > condition to be safe?
> > 
> > I think it's just an oversight in bspec. I read through the hsd and
> > IIRC it did specify that it's VT-d only. Also real life confirms
> > it. No problems whatsoever when VT-d is disabled.
> 
> I notice there are additional bits that we should set to apply this
> workaround to planes 2, 3, and 4, but since i915 still artificially
> limits async flips to just the primary plane, only programming bits 1:0
> should be fine for now; we'll just need to remember to extend this
> workaround if we do start allowing async flips on other planes in the
> future.

Aye. gen8_de_pipe_flip_done_mask() is the other place where we
still hardcode this for plane 1 only. I think the rest of the code
I did end up making more or less plane agnostic already.

I was considering at least parametrizing the register defines but
then I got a nagging feeling that I once ran into some issues while
trying to stick non-constant numbers into REG_BIT & co. So I
decided to hardcode plane 1 for the moment.

> 
> Reviewed-by: Matt Roper <matthew.d.roper@intel.com>

Thanks. Pushed.

-- 
Ville Syrjälä
Intel