[PATCH 1/2] drm/i915/guc: Don't check CT descriptor status before CT write / read

[Matthew Brost]

Don't check CT descriptor status, unless CONFIG_DRM_I915_DEBUG_GUC is
set, before CT write / read as this could result in a read across the
PCIe bus thus adding latency to every CT write / read. On well behavied
systems this vaue should always read as zero. For some reason it doesn't
the CT channel is broken and will eventually recover from a GT reset,
albeit the GT reset will not be triggered immediately by seeing that
descriptor status is non-zero.

v2:
 (CI)
  - Fix build error (hide corrupted label in write function behind
    CONFIG_DRM_I915_DEBUG_GUC)

Signed-off-by: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
index de89d40abd38d..948cf31429412 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
@@ -379,8 +379,10 @@ static int ct_write(struct intel_guc_ct *ct,
 	u32 *cmds = ctb->cmds;
 	unsigned int i;
 
+#ifdef CONFIG_DRM_I915_DEBUG_GUC
 	if (unlikely(desc->status))
 		goto corrupted;
+#endif
 
 	GEM_BUG_ON(tail > size);
 
@@ -445,11 +447,13 @@ static int ct_write(struct intel_guc_ct *ct,
 
 	return 0;
 
+#ifdef CONFIG_DRM_I915_DEBUG_GUC
 corrupted:
 	CT_ERROR(ct, "Corrupted descriptor head=%u tail=%u status=%#x\n",
 		 desc->head, desc->tail, desc->status);
 	ctb->broken = true;
 	return -EPIPE;
+#endif
 }
 
 /**
@@ -815,8 +819,10 @@ static int ct_read(struct intel_guc_ct *ct, struct ct_incoming_msg **msg)
 	if (unlikely(ctb->broken))
 		return -EPIPE;
 
+#ifdef CONFIG_DRM_I915_DEBUG_GUC
 	if (unlikely(desc->status))
 		goto corrupted;
+#endif
 
 	GEM_BUG_ON(head > size);
 
-- 
2.34.1