[PATCH 07/11] drm/i915/skl+: Fail the flip if ddb min requirement exceeds pipe allocation

[Mahesh Kumar <mahesh1.kumar@intel.com>]

DDB minimum requirement of crtc configuration (cumulative of all the
enabled planes in crtc) may exceed the allocated DDB for crtc/pipe.
This patch make changes to fail the flip/ioctl if minimum requirement
for pipe exceeds the total ddb allocated to the pipe.
Previously it succeeded but making alloc_size a negative value. Which
will make subsequent calculations for plane ddb allocation bogus & may
lead to screen corruption or system hang.

Changes from V1:
 - Improve commit message as per Ander's comment
 - Remove extra parentheses (Ander)

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 2a4e9d89cd6f..c0f6aeab0390 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3591,6 +3591,7 @@ skl_allocate_pipe_ddb(struct intel_crtc_state *cstate,
 	int num_active;
 	unsigned plane_data_rate[I915_MAX_PLANES] = {};
 	unsigned plane_y_data_rate[I915_MAX_PLANES] = {};
+	uint16_t total_min_blocks = 0;
 
 	/* Clear the partitioning for disabled planes. */
 	memset(ddb->plane[pipe], 0, sizeof(ddb->plane[pipe]));
@@ -3618,10 +3619,18 @@ skl_allocate_pipe_ddb(struct intel_crtc_state *cstate,
 	 */
 
 	for_each_plane_id_on_crtc(intel_crtc, plane_id) {
-		alloc_size -= minimum[plane_id];
-		alloc_size -= y_minimum[plane_id];
+		total_min_blocks += minimum[plane_id];
+		total_min_blocks += y_minimum[plane_id];
 	}
 
+	if (total_min_blocks > alloc_size) {
+		DRM_DEBUG_KMS("Requested display configuration exceeds system DDB limitations");
+		DRM_DEBUG_KMS("minimum required %d/%d\n", total_min_blocks,
+							alloc_size);
+		return-EINVAL;
+	}
+
+	alloc_size -= total_min_blocks;
 	ddb->plane[pipe][PLANE_CURSOR].start = alloc->end - minimum[PLANE_CURSOR];
 	ddb->plane[pipe][PLANE_CURSOR].end = alloc->end;
 
-- 
2.11.0

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