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

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

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?

> +
>  	return 0;
>  }
>  
> -- 
> 2.39.0

-- 
Ville Syrjälä
Intel