4 files changed, 35 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 7062cde..1238104 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -3326,8 +3326,10 @@ static int i915_engine_info(struct seq_file *m, void *unused)
 			ptr = I915_READ(RING_CONTEXT_STATUS_PTR(engine));
 			read = GEN8_CSB_READ_PTR(ptr);
 			write = GEN8_CSB_WRITE_PTR(ptr);
-			seq_printf(m, "\tExeclist CSB read %d, write %d, interrupt posted? %s\n",
-				   read, write,
+			seq_printf(m, "\tExeclist CSB read %d [%d cached], write %d [%d from hws], interrupt posted? %s\n",
+				   read, engine->csb_head,
+				   write,
+				   intel_read_status_page(engine, intel_hws_csb_write_index(engine->i915)),
 				   yesno(test_bit(ENGINE_IRQ_EXECLIST,
 						  &engine->irq_posted)));
 			if (read >= GEN8_CSB_ENTRIES)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9dba1b2..b657df7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -4400,4 +4400,12 @@ int remap_io_mapping(struct vm_area_struct *vma,
 		     unsigned long addr, unsigned long pfn, unsigned long size,
 		     struct io_mapping *iomap);
 
+static inline int intel_hws_csb_write_index(struct drm_i915_private *i915)
+{
+	if (INTEL_GEN(i915) >= 10)
+		return CNL_HWS_CSB_WRITE_INDEX;
+	else
+		return I915_HWS_CSB_WRITE_INDEX;
+}
+
 #endif
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 6d7bbb9..1960ba5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -539,8 +539,6 @@ static void intel_lrc_irq_handler(unsigned long data)
 	 * new request (outside of the context-switch interrupt).
 	 */
 	while (test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted)) {
-		u32 __iomem *csb_mmio =
-			dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine));
 		/* The HWSP contains a (cacheable) mirror of the CSB */
 		const u32 *buf =
 			&engine->status_page.page_addr[I915_HWS_CSB_BUF0_INDEX];
@@ -550,6 +548,7 @@ static void intel_lrc_irq_handler(unsigned long data)
 		if (unlikely(engine->csb_use_mmio)) {
 			buf = (u32 * __force)
 				(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_BUF_LO(engine, 0)));
+			engine->csb_head = -1; /* force mmio read of CSB ptrs */
 		}
 
 		/* The write will be ordered by the uncached read (itself
@@ -563,9 +562,19 @@ static void intel_lrc_irq_handler(unsigned long data)
 		 * is set and we do a new loop.
 		 */
 		__clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
-		head = readl(csb_mmio);
-		tail = GEN8_CSB_WRITE_PTR(head);
-		head = GEN8_CSB_READ_PTR(head);
+		if (unlikely(engine->csb_head == -1)) { /* following a reset */
+			head = readl(dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)));
+			tail = GEN8_CSB_WRITE_PTR(head);
+			head = GEN8_CSB_READ_PTR(head);
+			engine->csb_head = head;
+		} else {
+			const int write_idx =
+				intel_hws_csb_write_index(dev_priv) -
+				I915_HWS_CSB_BUF0_INDEX;
+
+			head = engine->csb_head;
+			tail = READ_ONCE(buf[write_idx]);
+		}
 		while (head != tail) {
 			struct drm_i915_gem_request *rq;
 			unsigned int status;
@@ -619,8 +628,11 @@ static void intel_lrc_irq_handler(unsigned long data)
 				   !(status & GEN8_CTX_STATUS_ACTIVE_IDLE));
 		}
 
-		writel(_MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, head << 8),
-		       csb_mmio);
+		if (head != engine->csb_head) {
+			engine->csb_head = head;
+			writel(_MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, head << 8),
+			       dev_priv->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)));
+		}
 	}
 
 	if (execlists_elsp_ready(engine))
@@ -1269,6 +1281,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
 	I915_WRITE(GEN8_GT_IIR(gtiir[engine->id]),
 		   GT_CONTEXT_SWITCH_INTERRUPT << engine->irq_shift);
 	clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
+	engine->csb_head = -1;
 
 	/* After a GPU reset, we may have requests to replay */
 	submit = false;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 5c055b6..abf171c 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -391,6 +391,7 @@ struct intel_engine_cs {
 	struct rb_root execlist_queue;
 	struct rb_node *execlist_first;
 	unsigned int fw_domains;
+	unsigned int csb_head;
 	bool csb_use_mmio;
 
 	/* Contexts are pinned whilst they are active on the GPU. The last
@@ -498,6 +499,8 @@ intel_write_status_page(struct intel_engine_cs *engine, int reg, u32 value)
 #define I915_GEM_HWS_SCRATCH_ADDR (I915_GEM_HWS_SCRATCH_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
 
 #define I915_HWS_CSB_BUF0_INDEX		0x10
+#define I915_HWS_CSB_WRITE_INDEX	0x1f
+#define CNL_HWS_CSB_WRITE_INDEX		0x2f
 
 struct intel_ring *
 intel_engine_create_ring(struct intel_engine_cs *engine, int size);