[PATCH 5/6] drm/i915/gsc: Disable GSC engine and power well if FW is not selected

[Daniele Ceraolo Spurio]

From: Jonathan Cavitt <jonathan.cavitt at intel.com>

The GSC CS is only used for communicating with the GSC FW, so no need to
initialize it if we're not going to use the FW. If we're not using
neither the engine nor the microcontoller, then we can also disable the
power well.

IMPORTANT: lack of GSC FW breaks media C6 due to opposing requirements
between CS setup and forcewake idleness. See in-code comment for detail.

Signed-off-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Cc: Matt Roper <matthew.d.roper at intel.com>
Cc: John C Harrison <John.C.Harrison at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Vinay Belgaumkar <vinay.belgaumkar at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_engine_cs.c | 18 ++++++++++++++++++
 drivers/gpu/drm/i915/intel_uncore.c       |  3 +++
 2 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index c33e0d72d670..99c4b866addd 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -894,6 +894,24 @@ static intel_engine_mask_t init_engine_mask(struct intel_gt *gt)
 	engine_mask_apply_compute_fuses(gt);
 	engine_mask_apply_copy_fuses(gt);
 
+	/*
+	 * The only use of the GSC CS is to load and communicate with the GSC
+	 * FW, so we have no use for it if we don't have the FW.
+	 *
+	 * IMPORTANT: in cases where we don't have the GSC FW, we have a
+	 * catch-22 situation that breaks media C6 due to 2 requirements:
+	 * 1) once turned on, the GSC power well will not go to sleep unless the
+	 *    GSC FW is loaded.
+	 * 2) to enable idling (which is required for media C6) we need to
+	 *    initialize the IDLE_MSG register for the GSC CS and do at least 1
+	 *    submission, which will wake up the GSC power well.
+	 */
+	if (__HAS_ENGINE(info->engine_mask, GSC0) && !intel_uc_wants_gsc_uc(&gt->uc)) {
+		drm_notice(&gt->i915->drm,
+			   "No GSC FW selected, disabling GSC CS and media C6\n");
+		info->engine_mask &= ~BIT(GSC0);
+	}
+
 	return info->engine_mask;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index c1befa33ff59..e63d957b59eb 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -2701,6 +2701,9 @@ void intel_uncore_prune_engine_fw_domains(struct intel_uncore *uncore,
 		if (fw_domains & BIT(domain_id))
 			fw_domain_fini(uncore, domain_id);
 	}
+
+	if ((fw_domains & BIT(FW_DOMAIN_ID_GSC)) && !HAS_ENGINE(gt, GSC0))
+		fw_domain_fini(uncore, FW_DOMAIN_ID_GSC);
 }
 
 static void driver_flr(struct intel_uncore *uncore)
-- 
2.37.3