[PATCH] drm/i915/gt: Do not consider preemption during execlists_dequeue for gen8

[Nitin Gote]

We're seeing a GPU HANG issue on a CHV platform, which was caused by
bac24f59f454 ("drm/i915/execlists: Enable coarse preemption boundaries for gen8").

Gen8 platform has only timeslice and doesn't support a preemption mechanism
as engines do not have a preemption timer and doesn't send an irq if the
preemption timeout expires. So, add a fix to not consider preemption
during dequeuing for gen8 platforms.

Also move can_preemt() above need_preempt() function to resolve implicit
declaration of function ‘can_preempt' error and make can_preempt()
function param as const to resolve error: passing argument 1 of
‘can_preempt’ discards ‘const’ qualifier from the pointer target type.

Fixes: bac24f59f454 ("drm/i915/execlists: Enable coarse preemption boundaries for gen8")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11396
Suggested-by: Andi Shyti <andi.shyti at intel.com>
Signed-off-by: Nitin Gote <nitin.r.gote at intel.com>
Cc: Chris Wilson <chris.p.wilson at linux.intel.com>
CC: <stable at vger.kernel.org> # v5.2+
---
 .../drm/i915/gt/intel_execlists_submission.c  | 24 ++++++++++++-------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
index 21829439e686..30631cc690f2 100644
--- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
+++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
@@ -294,11 +294,26 @@ static int virtual_prio(const struct intel_engine_execlists *el)
 	return rb ? rb_entry(rb, struct ve_node, rb)->prio : INT_MIN;
 }
 
+static bool can_preempt(const struct intel_engine_cs *engine)
+{
+	if (GRAPHICS_VER(engine->i915) > 8)
+		return true;
+
+	if (IS_CHERRYVIEW(engine->i915) || IS_BROADWELL(engine->i915))
+		return false;
+
+	/* GPGPU on bdw requires extra w/a; not implemented */
+	return engine->class != RENDER_CLASS;
+}
+
 static bool need_preempt(const struct intel_engine_cs *engine,
 			 const struct i915_request *rq)
 {
 	int last_prio;
 
+	if ((GRAPHICS_VER(engine->i915) <= 8) && can_preempt(engine))
+		return false;
+
 	if (!intel_engine_has_semaphores(engine))
 		return false;
 
@@ -3313,15 +3328,6 @@ static void remove_from_engine(struct i915_request *rq)
 	i915_request_notify_execute_cb_imm(rq);
 }
 
-static bool can_preempt(struct intel_engine_cs *engine)
-{
-	if (GRAPHICS_VER(engine->i915) > 8)
-		return true;
-
-	/* GPGPU on bdw requires extra w/a; not implemented */
-	return engine->class != RENDER_CLASS;
-}
-
 static void kick_execlists(const struct i915_request *rq, int prio)
 {
 	struct intel_engine_cs *engine = rq->engine;
-- 
2.25.1