[Intel-gfx] [PATCH] drm/i915/gt: Stall around xcs invalidations on tgl

[Chris Wilson]

Whether this is an arbitrary stall or a vital ingredient, neverthess the
impact is noticeable. If we do not have the stall around the xcs
invalidation before a request, writes within that request sometimes go
astray.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2169
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 353b1717fe84..7d914527d236 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -4761,10 +4761,12 @@ static int gen12_emit_flush_render(struct i915_request *request,
 
 static int gen12_emit_flush(struct i915_request *request, u32 mode)
 {
+#define WA_CNT 16 /* Magic delay or size of some internal pipelined buffer? */
 	intel_engine_mask_t aux_inv = 0;
 	u32 cmd, *cs;
+	int n;
 
-	cmd = 4;
+	cmd = 4 * WA_CNT;
 	if (mode & EMIT_INVALIDATE)
 		cmd += 2;
 	if (mode & EMIT_INVALIDATE)
@@ -4781,7 +4783,8 @@ static int gen12_emit_flush(struct i915_request *request, u32 mode)
 
 	cmd = MI_FLUSH_DW + 1;
 
-	/* We always require a command barrier so that subsequent
+	/*
+	 * We always require a command barrier so that subsequent
 	 * commands, such as breadcrumb interrupts, are strictly ordered
 	 * wrt the contents of the write cache being flushed to memory
 	 * (and thus being coherent from the CPU).
@@ -4794,10 +4797,12 @@ static int gen12_emit_flush(struct i915_request *request, u32 mode)
 			cmd |= MI_INVALIDATE_BSD;
 	}
 
-	*cs++ = cmd;
-	*cs++ = LRC_PPHWSP_SCRATCH_ADDR;
-	*cs++ = 0; /* upper addr */
-	*cs++ = 0; /* value */
+	for (n = 0; n < WA_CNT; n++) {
+		*cs++ = cmd;
+		*cs++ = LRC_PPHWSP_SCRATCH_ADDR;
+		*cs++ = 0; /* upper addr */
+		*cs++ = 0; /* value */
+	}
 
 	if (aux_inv) { /* hsdes: 1809175790 */
 		struct intel_engine_cs *engine;
@@ -4818,6 +4823,7 @@ static int gen12_emit_flush(struct i915_request *request, u32 mode)
 	intel_ring_advance(request, cs);
 
 	return 0;
+#undef WA_CNT
 }
 
 static void assert_request_valid(struct i915_request *rq)
-- 
2.20.1