[PATCH] drm/i915/mtl: Disable stolen memory backed FB for A0

[Nirmoy Das]

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.

Cc: Matthew Auld <matthew.auld at intel.com>
Cc: Andi Shyti <andi.shyti at linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Cc: Lucas De Marchi <lucas.demarchi at intel.com>

Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
index d8e06e783e30..56ccfcbdbce1 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
@@ -535,6 +535,16 @@ 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.
+	 * hsdes: 22016134735
+	 */
+	if (IS_MTL_GRAPHICS_STEP(i915, M, STEP_A0, STEP_B0) ||
+	    IS_MTL_GRAPHICS_STEP(i915, P, STEP_A0, STEP_B0))
+		i915->dsm.usable_size = 0;
+
 	return 0;
 }
 
-- 
2.39.0