[Intel-gfx] [PATCH 7/8] drm/i915: fixup the initial fb base on DG1

[Ville Syrjälä]

On Mon, Mar 07, 2022 at 10:32:36AM +0000, Matthew Auld wrote:
> On 04/03/2022 19:33, Ville Syrjälä wrote:
> > On Fri, Mar 04, 2022 at 05:23:32PM +0000, Matthew Auld wrote:
> >> The offset we get looks to be the exact start of DSM, but the
> >> inital_plane_vma expects the address to be relative.
> >>
> >> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> >> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> >> ---
> >>   .../drm/i915/display/intel_plane_initial.c    | 22 +++++++++++++++----
> >>   1 file changed, 18 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/display/intel_plane_initial.c b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> >> index f797fcef18fc..b39d3a8dfe45 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_plane_initial.c
> >> +++ b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> >> @@ -56,10 +56,24 @@ initial_plane_vma(struct drm_i915_private *i915,
> >>   	if (!mem || plane_config->size == 0)
> >>   		return NULL;
> >>   
> >> -	base = round_down(plane_config->base,
> >> -			  I915_GTT_MIN_ALIGNMENT);
> >> -	size = round_up(plane_config->base + plane_config->size,
> >> -			mem->min_page_size);
> >> +	base = plane_config->base;
> >> +	if (IS_DGFX(i915)) {
> >> +		/*
> >> +		 * On discrete the base address should be somewhere in LMEM, but
> >> +		 * depending on the size of LMEM the base address might
> >> +		 * intersect with the start of DSM, like on DG1, in which case
> >> +		 * we need the relative address. In such cases we might also
> >> +		 * need to choose between inital fb vs fbc, if space is limited.
> >> +		 *
> >> +		 * On future discrete HW, like DG2, we should be able to just
> >> +		 * allocate directly from LMEM, due to larger LMEM size.
> >> +		 */
> >> +		if (base >= i915->dsm.start)
> >> +			base -= i915->dsm.start;
> > 
> > Subsequent code expects the object to actually be inside stolen.
> > If that is not the case we should just give up.
> 
> Thanks for taking a look at this. Is that subsequent code outside 
> initial_plane_vma()? In the next patch this is now using LMEM directly 
> for dg2. Would that blow up somewhere else?

It uses i915_gem_object_create_stolen_for_preallocated() which assumes
the stuff is inside stolen.

> > The fact that we fail to confirm any of that on integrated
> > parts has always bugged me, but not enough to actually do
> > anything about it. Such a check would be somewhat more involved
> > since we'd have to look at the PTEs. But on discrete sounds like
> > we can get away with a trivial check.
> 
> Which PTEs?

The PTEs the plane is actually using. We have no idea where they
actually point to and just assume they represent a 1:1 mapping of
stolen.

I suppose with lmem we'll just start assuming a 1:1 mapping of
the whole lmem rather than just stolen.

-- 
Ville Syrjälä
Intel