Re: [Intel-gfx] [PATCH v3] drm/i915/mtl: Disable stolen memory backed FB for A0

["Hogander, Jouni" <jouni.hogander@intel.com>]

On Tue, 2023-04-04 at 23:26 +0200, Das, Nirmoy wrote:
> 
> On 4/4/2023 8:27 PM, Ville Syrjälä wrote:
> > On Tue, Apr 04, 2023 at 08:13:42PM +0200, Nirmoy Das wrote:
> > > Stolen memory is not usable for MTL A0 stepping beyond
> > > certain access size and we have no control over userspace
> > > access size of /dev/fb which can be backed by stolen memory.
> > > So disable stolen memory backed fb by setting i915-
> > > >dsm.usable_size
> > > to zero.
> > > 
> > > v2: remove hsdes reference and fix commit message(Andi)
> > > v3: use revid as we want to target SOC stepping(Radhakrishna)
> > > 
> > > Cc: Matthew Auld <matthew.auld@intel.com>
> > > Cc: Andi Shyti <andi.shyti@linux.intel.com>
> > > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> > > Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> > > Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
> > > Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> > > Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
> > > ---
> > >   drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 8 ++++++++
> > >   1 file changed, 8 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> > > b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> > > index 8ac376c24aa2..ee492d823f1b 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> > > @@ -535,6 +535,14 @@ static int i915_gem_init_stolen(struct
> > > intel_memory_region *mem)
> > >         /* Basic memrange allocator for stolen space. */
> > >         drm_mm_init(&i915->mm.stolen, 0, i915->dsm.usable_size);
> > >   
> > > +       /*
> > > +        * Access to stolen lmem beyond certain size for MTL A0
> > > stepping
> > > +        * would crash the machine. Disable stolen lmem for
> > > userspace access
> > > +        * by setting usable_size to zero.
> > > +        */
> > > +       if (IS_METEORLAKE(i915) && INTEL_REVID(i915) == 0x0)
> > > +               i915->dsm.usable_size = 0;
> > That certainly won't prevent FBC from using stolen.
> > Are we sure that FBC accesses are fine?
> 
> I think so. I remember Jouni tested this patch internally to unblock
> a 
> FBC test.
> 
> Jouni, could you please share your thoughts. I can't seem to find the
> internal JIRA reference right now.

I tested this patch and it was fixing the problem it was targeted. I
didn't noticed any issue back then.

> 
> 
> Regards,
> 
> Nirmoy
> 
> > 
> > > +
> > >         return 0;
> > >   }
> > >   
> > > -- 
> > > 2.39.0