RDMA/hns: Add a check to ensure integer mtu is positive

GCC may reports an running time assert error when a value calculated from
ib_mtu_enum_to_int() is using as 'val' in FIELD_PREDP:

include/linux/compiler_types.h:328:38: error: call to
'__compiletime_assert_1524' declared with attribute error: FIELD_PREP:
value too large for the field

So a check is added about whether integer mtu from ib_mtu_enum_to_int() is
negative to avoid this warning.

Link: https://lore.kernel.org/r/1624262443-24528-3-git-send-email-liweihang@huawei.comReported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/hns/hns_roce_hw_v2.c

@@ -4509,12 +4509,13 @@ static int modify_qp_init_to_rtr(struct ib_qp *ibqp,
 	struct ib_device *ibdev = &hr_dev->ib_dev;
 	dma_addr_t trrl_ba;
 	dma_addr_t irrl_ba;
-	enum ib_mtu mtu;
+	enum ib_mtu ib_mtu;
 	u8 lp_pktn_ini;
 	u64 *mtts;
 	u8 *dmac;
 	u8 *smac;
 	u32 port;
+	int mtu;
 	int ret;
 
 	ret = config_qp_rq_buf(hr_dev, hr_qp, context, qpc_mask);
@@ -4598,19 +4599,23 @@ static int modify_qp_init_to_rtr(struct ib_qp *ibqp,
 	roce_set_field(qpc_mask->byte_52_udpspn_dmac, V2_QPC_BYTE_52_DMAC_M,
 		       V2_QPC_BYTE_52_DMAC_S, 0);
 
-	mtu = get_mtu(ibqp, attr);
-	hr_qp->path_mtu = mtu;
+	ib_mtu = get_mtu(ibqp, attr);
+	hr_qp->path_mtu = ib_mtu;
+
+	mtu = ib_mtu_enum_to_int(ib_mtu);
+	if (WARN_ON(mtu < 0))
+		return -EINVAL;
 
 	if (attr_mask & IB_QP_PATH_MTU) {
 		roce_set_field(context->byte_24_mtu_tc, V2_QPC_BYTE_24_MTU_M,
-			       V2_QPC_BYTE_24_MTU_S, mtu);
+			       V2_QPC_BYTE_24_MTU_S, ib_mtu);
 		roce_set_field(qpc_mask->byte_24_mtu_tc, V2_QPC_BYTE_24_MTU_M,
 			       V2_QPC_BYTE_24_MTU_S, 0);
 	}
 
 #define MAX_LP_MSG_LEN 65536
 	/* MTU * (2 ^ LP_PKTN_INI) shouldn't be bigger than 64KB */
-	lp_pktn_ini = ilog2(MAX_LP_MSG_LEN / ib_mtu_enum_to_int(mtu));
+	lp_pktn_ini = ilog2(MAX_LP_MSG_LEN / mtu);
 
 	roce_set_field(context->byte_56_dqpn_err, V2_QPC_BYTE_56_LP_PKTN_INI_M,
 		       V2_QPC_BYTE_56_LP_PKTN_INI_S, lp_pktn_ini);