iommu/arm-smmu-v3: Properly handle the return value of arm_smmu_cmdq_build_cmd()

1. Build command CMD_SYNC cannot fail. So the return value can be ignored.
2. The arm_smmu_cmdq_build_cmd() almost never fails, the addition of
   "unlikely()" can optimize the instruction pipeline.
3. Check the return value in arm_smmu_cmdq_batch_add().

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20210818080452.2079-2-thunder.leizhen@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -409,10 +409,7 @@ static void __arm_smmu_cmdq_skip_err(struct arm_smmu_device *smmu,
 		dev_err(smmu->dev, "\t0x%016llx\n", (unsigned long long)cmd[i]);
 
 	/* Convert the erroneous command into a CMD_SYNC */
-	if (arm_smmu_cmdq_build_cmd(cmd, &cmd_sync)) {
-		dev_err(smmu->dev, "failed to convert to CMD_SYNC\n");
-		return;
-	}
+	arm_smmu_cmdq_build_cmd(cmd, &cmd_sync);
 
 	queue_write(Q_ENT(q, cons), cmd, q->ent_dwords);
 }
@@ -860,7 +857,7 @@ static int __arm_smmu_cmdq_issue_cmd(struct arm_smmu_device *smmu,
 {
 	u64 cmd[CMDQ_ENT_DWORDS];
 
-	if (arm_smmu_cmdq_build_cmd(cmd, ent)) {
+	if (unlikely(arm_smmu_cmdq_build_cmd(cmd, ent))) {
 		dev_warn(smmu->dev, "ignoring unknown CMDQ opcode 0x%x\n",
 			 ent->opcode);
 		return -EINVAL;
@@ -885,11 +882,20 @@ static void arm_smmu_cmdq_batch_add(struct arm_smmu_device *smmu,
 				    struct arm_smmu_cmdq_batch *cmds,
 				    struct arm_smmu_cmdq_ent *cmd)
 {
+	int index;
+
 	if (cmds->num == CMDQ_BATCH_ENTRIES) {
 		arm_smmu_cmdq_issue_cmdlist(smmu, cmds->cmds, cmds->num, false);
 		cmds->num = 0;
 	}
-	arm_smmu_cmdq_build_cmd(&cmds->cmds[cmds->num * CMDQ_ENT_DWORDS], cmd);
+
+	index = cmds->num * CMDQ_ENT_DWORDS;
+	if (unlikely(arm_smmu_cmdq_build_cmd(&cmds->cmds[index], cmd))) {
+		dev_warn(smmu->dev, "ignoring unknown CMDQ opcode 0x%x\n",
+			 cmd->opcode);
+		return;
+	}
+
 	cmds->num++;
 }