drm/xe: enable lite restore

The lite restore is a performance improvement feature which avoids
unnecessary context switch (flush, save and restore) if the incoming
context has a ContextID matching that of the outgoing context. The
scheduling is done by the GuC firmware, so on the driver side it's
just a matter of setting corresponding GUC_CTL_FEATURE flag.
This is supposed to be enabled by default, thus the flag is set
unconditionally.

Signed-off-by: Fei Yang <fei.yang@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241017162710.942553-2-fei.yang@intel.com

drivers/gpu/drm/xe/xe_guc.c

@@ -70,7 +70,7 @@ static u32 guc_ctl_debug_flags(struct xe_guc *guc)
 
 static u32 guc_ctl_feature_flags(struct xe_guc *guc)
 {
-	u32 flags = 0;
+	u32 flags = GUC_CTL_ENABLE_LITE_RESTORE;
 
 	if (!guc_to_xe(guc)->info.skip_guc_pc)
 		flags |= GUC_CTL_ENABLE_SLPC;

drivers/gpu/drm/xe/xe_guc_fwif.h

@@ -105,6 +105,7 @@ struct guc_update_exec_queue_policy {
 
 #define GUC_CTL_FEATURE			2
 #define   GUC_CTL_ENABLE_SLPC		BIT(2)
+#define   GUC_CTL_ENABLE_LITE_RESTORE	BIT(4)
 #define   GUC_CTL_DISABLE_SCHEDULER	BIT(14)
 
 #define GUC_CTL_DEBUG			3