drm/i915/guc: Prepare for error propagation

Currently guc_mmio_reg_add() relies on having enough memory available in
the array to add a new slot. It uses
`GEM_BUG_ON(count >= regset->size);` to protect going above the
threshold.

In order to allow guc_mmio_reg_add() to handle the memory allocation by
itself, it must return an error in case of failures.  Adjust return code
so this error can be propagated to the callers of guc_mmio_reg_add() and
guc_mmio_regset_init().

No intended change in behavior.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220208070141.2095177-2-lucas.demarchi@intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c

@@ -224,7 +224,7 @@ static int guc_mmio_reg_cmp(const void *a, const void *b)
 	return (int)ra->offset - (int)rb->offset;
 }
 
-static void guc_mmio_reg_add(struct temp_regset *regset,
+static long __must_check guc_mmio_reg_add(struct temp_regset *regset,
 					  u32 offset, u32 flags)
 {
 	u32 count = regset->used;
@@ -244,7 +244,7 @@ static void guc_mmio_reg_add(struct temp_regset *regset,
 	 */
 	if (bsearch(&reg, regset->registers, count,
 		    sizeof(reg), guc_mmio_reg_cmp))
-		return;
+		return 0;
 
 	slot = &regset->registers[count];
 	regset->used++;
@@ -257,6 +257,8 @@ static void guc_mmio_reg_add(struct temp_regset *regset,
 
 		swap(slot[1], slot[0]);
 	}
+
+	return 0;
 }
 
 #define GUC_MMIO_REG_ADD(regset, reg, masked) \
@@ -264,32 +266,35 @@ static void guc_mmio_reg_add(struct temp_regset *regset,
 			 i915_mmio_reg_offset((reg)), \
 			 (masked) ? GUC_REGSET_MASKED : 0)
 
-static void guc_mmio_regset_init(struct temp_regset *regset,
+static int guc_mmio_regset_init(struct temp_regset *regset,
 				struct intel_engine_cs *engine)
 {
 	const u32 base = engine->mmio_base;
 	struct i915_wa_list *wal = &engine->wa_list;
 	struct i915_wa *wa;
 	unsigned int i;
+	int ret = 0;
 
 	regset->used = 0;
 
-	GUC_MMIO_REG_ADD(regset, RING_MODE_GEN7(base), true);
-	GUC_MMIO_REG_ADD(regset, RING_HWS_PGA(base), false);
-	GUC_MMIO_REG_ADD(regset, RING_IMR(base), false);
+	ret |= GUC_MMIO_REG_ADD(regset, RING_MODE_GEN7(base), true);
+	ret |= GUC_MMIO_REG_ADD(regset, RING_HWS_PGA(base), false);
+	ret |= GUC_MMIO_REG_ADD(regset, RING_IMR(base), false);
 
 	for (i = 0, wa = wal->list; i < wal->count; i++, wa++)
-		GUC_MMIO_REG_ADD(regset, wa->reg, wa->masked_reg);
+		ret |= GUC_MMIO_REG_ADD(regset, wa->reg, wa->masked_reg);
 
 	/* Be extra paranoid and include all whitelist registers. */
 	for (i = 0; i < RING_MAX_NONPRIV_SLOTS; i++)
-		GUC_MMIO_REG_ADD(regset,
+		ret |= GUC_MMIO_REG_ADD(regset,
 					RING_FORCE_TO_NONPRIV(base, i),
 					false);
 
 	/* add in local MOCS registers */
 	for (i = 0; i < GEN9_LNCFCMOCS_REG_COUNT; i++)
-		GUC_MMIO_REG_ADD(regset, GEN9_LNCFCMOCS(i), false);
+		ret |= GUC_MMIO_REG_ADD(regset, GEN9_LNCFCMOCS(i), false);
+
+	return ret ? -1 : 0;
 }
 
 static int guc_mmio_reg_state_query(struct intel_guc *guc)