From dd39014efd5e31ef39c4dd153c94c58d1c028250 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Sun, 10 Nov 2019 18:57:51 +0000
Subject: drm/i915/execlists: Reduce barrier on context switch to a wmb()
Git-commit: 69a48c1d28e05893607b89515442b993cd5326ed
Patch-mainline: v5.6-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322
Having been forced to reduce Braswell back to using the aliasing ppgtt,
the coherency issue we previously observed cannot impact us. Reduce the
performance penalty imposed on all platforms from using the mfence to a
mere sfence.
References: cf66b8a0ba14 ("drm/i915/execlists: Apply a full mb before execution for Braswell")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191110185806.17413-10-chris@chris-wilson.co.uk
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/i915/gt/intel_lrc.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 935655b274f7..f51107e566eb 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1241,13 +1241,8 @@ static u64 execlists_update_context(struct i915_request *rq)
* may not be visible to the HW prior to the completion of the UC
* register write and that we may begin execution from the context
* before its image is complete leading to invalid PD chasing.
- *
- * Furthermore, Braswell, at least, wants a full mb to be sure that
- * the writes are coherent in memory (visible to the GPU) prior to
- * execution, and not just visible to other CPUs (as is the result of
- * wmb).
*/
- mb();
+ wmb();
/* Wa_1607138340:tgl */
if (IS_TGL_REVID(rq->i915, TGL_REVID_A0, TGL_REVID_A0))
--
2.28.0