drm/i915/gt: Track if an engine requires forcewake w/a

Sometimes an engine might need to keep forcewake active while it is busy
submitting requests for a particular workaround. Track such nuisance
with engine->fw_domain.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200604153145.21068-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_engine_types.h

@@ -24,6 +24,7 @@
 #include "i915_selftest.h"
 #include "intel_sseu.h"
 #include "intel_timeline_types.h"
+#include "intel_uncore.h"
 #include "intel_wakeref.h"
 #include "intel_workarounds_types.h"
 
@@ -313,6 +314,16 @@ struct intel_engine_cs {
 	u32 context_size;
 	u32 mmio_base;
 
+	/*
+	 * Some w/a require forcewake to be held (which prevents RC6) while
+	 * a particular engine is active. If so, we set fw_domain to which
+	 * domains need to be held for the duration of request activity,
+	 * and 0 if none. We try to limit the duration of the hold as much
+	 * as possible.
+	 */
+	enum forcewake_domains fw_domain;
+	atomic_t fw_active;
+
 	unsigned long context_tag;
 
 	struct rb_node uabi_node;

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -1373,6 +1373,8 @@ __execlists_schedule_in(struct i915_request *rq)
 	ce->lrc.ccid |= engine->execlists.ccid;
 
 	__intel_gt_pm_get(engine->gt);
+	if (engine->fw_domain && !atomic_fetch_inc(&engine->fw_active))
+		intel_uncore_forcewake_get(engine->uncore, engine->fw_domain);
 	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_IN);
 	intel_engine_context_in(engine);
 
@@ -1441,6 +1443,8 @@ __execlists_schedule_out(struct i915_request *rq,
 	intel_context_update_runtime(ce);
 	intel_engine_context_out(engine);
 	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
+	if (engine->fw_domain && !atomic_dec_return(&engine->fw_active))
+		intel_uncore_forcewake_put(engine->uncore, engine->fw_domain);
 	intel_gt_pm_put_async(engine->gt);
 
 	/*