Re: [PATCH v2 08/15] drm/i915: Fix region start during initial plane readout

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

On Tue, Dec 19, 2023 at 02:01:15AM +0200, Ville Syrjälä wrote:
> On Mon, Dec 18, 2023 at 02:00:10PM +0100, Andrzej Hajda wrote:
> > On 15.12.2023 11:59, Ville Syrjala wrote:
> > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > 
> > > On MTL the stolen region starts at offset 8MiB from the start of
> > > LMEMBAR. The dma addresses are thus also offset by 8MiB. However the
> > > mm_node/etc. is zero based, and i915_pages_create_for_stolen() will
> > > add the appropriate region.start into the sg dma address. So when
> > > we do the readout we need to convert the dma address read from
> > > the PTE to be zero based as well.
> > > 
> > > Note that currently we don't take this path on MTL, but we should
> > > and thus this needs to be fixed. For lmem this works correctly
> > > already as the lmem region.start==0.
> > > 
> > > While at it let's also make sure the address points to somewhere within
> > > the memory region. We don't need to check the size as
> > > i915_gem_object_create_region_at() should later fail if the object size
> > > exceeds the region size.
> > > 
> > > Cc: Paz Zcharya <pazz@chromium.org>
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > ---
> > >   drivers/gpu/drm/i915/display/intel_plane_initial.c | 8 +++++---
> > >   1 file changed, 5 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/display/intel_plane_initial.c b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> > > index ffc92b18fcf5..db594ccf0323 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_plane_initial.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> > > @@ -79,16 +79,18 @@ initial_plane_vma(struct drm_i915_private *i915,
> > >   		 * We don't currently expect this to ever be placed in the
> > >   		 * stolen portion.
> > >   		 */
> > > -		if (phys_base >= resource_size(&mem->region)) {
> > > +		if (phys_base < mem->region.start || phys_base > mem->region.end) {
> > 
> > Maybe better:
> > phys_base + fb_size > mem->region.end" ?
> > Btw it seems redundant with later checks in 
> > i915_gem_object_create_region_at.
> > IMO at this moment we need only check if "phys_base -= 
> > mem->region.start" makes sense.
> 
> Yeah, I guess that alone would be sufficient. I left out the size
> check exactly because I knew it would fail later, and making an
> accurate check here (with page size rounding and whatnot) would
> be tedious. But this should also be true when the start offset
> is past the end of the region as well, so yeah I suppose I can
> just drop the second check.

After further pondering I think I'm leaning towards keeping this
as is, just to give a slightly more obvious debug message.

> 
> 
> > 
> > Regards
> > Andrzej
> > 
> > 
> > >   			drm_err(&i915->drm,
> > > -				"Initial plane programming using invalid range, phys_base=%pa\n",
> > > -				&phys_base);
> > > +				"Initial plane programming using invalid range, phys_base=%pa (%s [%pa-%pa])\n",
> > > +				&phys_base, mem->region.name, &mem->region.start, &mem->region.end);
> > >   			return NULL;
> > >   		}
> > >   
> > >   		drm_dbg(&i915->drm,
> > >   			"Using phys_base=%pa, based on initial plane programming\n",
> > >   			&phys_base);
> > > +
> > > +		phys_base -= mem->region.start;
> > >   	} else {
> > >   		phys_base = base;
> > >   		mem = i915->mm.stolen_region;
> 
> -- 
> Ville Syrjälä
> Intel

-- 
Ville Syrjälä
Intel