[Intel-gfx] [PATCH] drm/i915/gt: Only trust sseu subslice fuse if it is set

[Chris Wilson]

Since userspace cannot run without any subslices, it seems remarkable
that any system would be configured with all fused off. Ignore the fuse
register if it says 0.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/3022
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_sseu.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_sseu.c b/drivers/gpu/drm/i915/gt/intel_sseu.c
index 0d9f74aec8fe..99c992db2ce7 100644
--- a/drivers/gpu/drm/i915/gt/intel_sseu.c
+++ b/drivers/gpu/drm/i915/gt/intel_sseu.c
@@ -341,9 +341,10 @@ static void gen9_sseu_info_init(struct intel_gt *gt)
 	 * The subslice disable field is global, i.e. it applies
 	 * to each of the enabled slices.
 	 */
-	subslice_mask = (1 << sseu->max_subslices) - 1;
-	subslice_mask &= ~((fuse2 & GEN9_F2_SS_DIS_MASK) >>
-			   GEN9_F2_SS_DIS_SHIFT);
+	subslice_mask = (fuse2 & GEN9_F2_SS_DIS_MASK) >> GEN9_F2_SS_DIS_SHIFT;
+	if (!subslice_mask) /* Ignore the fuse if it says there is no HW */
+		subslice_mask = ~0u;
+	subslice_mask &= GENMASK(sseu->max_subslices - 1, 0);
 
 	/*
 	 * Iterate through enabled slices and subslices to
-- 
2.20.1