drm/i915/tgl: add GEN12_MAX_CONTEXT_HW_ID

Like Gen11, Gen12 has 11 available bits for the ctx id field. However,
the last value (0x7FF) is reserved to indicate engine idle, so we
need to reduce the maximum number of contexts by 1 compared to Gen11.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190817093902.2171-29-lucas.demarchi@intel.com

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -173,7 +173,9 @@ static inline int new_hw_id(struct drm_i915_private *i915, gfp_t gfp)
 
 	lockdep_assert_held(&i915->contexts.mutex);
 
-	if (INTEL_GEN(i915) >= 11)
+	if (INTEL_GEN(i915) >= 12)
+		max = GEN12_MAX_CONTEXT_HW_ID;
+	else if (INTEL_GEN(i915) >= 11)
 		max = GEN11_MAX_CONTEXT_HW_ID;
 	else if (USES_GUC_SUBMISSION(i915))
 		/*

drivers/gpu/drm/i915/i915_drv.h

@@ -1602,6 +1602,8 @@ struct drm_i915_private {
 #define MAX_CONTEXT_HW_ID (1<<21) /* exclusive */
 #define MAX_GUC_CONTEXT_HW_ID (1 << 20) /* exclusive */
 #define GEN11_MAX_CONTEXT_HW_ID (1<<11) /* exclusive */
+/* in Gen12 ID 0x7FF is reserved to indicate idle */
+#define GEN12_MAX_CONTEXT_HW_ID	(GEN11_MAX_CONTEXT_HW_ID - 1)
 		struct list_head hw_id_list;
 	} contexts;