[PATCH 5.14 098/172] RDMA/hns: Work around broken constant propagation in gcc 8

Greg Kroah-Hartman
2021-10-04T13:38:30Z

From: Jason Gunthorpe <jgg@nvidia.com>

[ Upstream commit 14351f08ed5c8b888cdd95651152db7e096ee27f ]

gcc 8.3 and 5.4 throw this:

In function 'modify_qp_init_to_rtr',
././include/linux/compiler_types.h:322:38: error: call to '__compiletime_assert_1859' declared with attribute error: FIELD_PREP: value too large for the field
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
[..]
drivers/infiniband/hw/hns/hns_roce_common.h:91:52: note: in expansion of macro 'FIELD_PREP'
*((__le32 *)ptr + (field_h) / 32) |= cpu_to_le32(FIELD_PREP( \
^~~~~~~~~~
drivers/infiniband/hw/hns/hns_roce_common.h:95:39: note: in expansion of macro '_hr_reg_write'
#define hr_reg_write(ptr, field, val) _hr_reg_write(ptr, field, val)
^~~~~~~~~~~~~
drivers/infiniband/hw/hns/hns_roce_hw_v2.c:4412:2: note: in expansion of macro 'hr_reg_write'
hr_reg_write(context, QPC_LP_PKTN_INI, lp_pktn_ini);

Because gcc has miscalculated the constantness of lp_pktn_ini:

mtu = ib_mtu_enum_to_int(ib_mtu);
if (WARN_ON(mtu < 0)) [..]
lp_pktn_ini = ilog2(MAX_LP_MSG_LEN / mtu);

Since mtu is limited to {256,512,1024,2048,4096} lp_pktn_ini is between 4
and 8 which is compatible with the 4 bit field in the FIELD_PREP.

Work around this broken compiler by adding a 'can never be true'
constraint on lp_pktn_ini's value which clears out the problem.

Fixes: f0cb411aad23 ("RDMA/hns: Use new interface to modify QP context")
Link: https://lore.kernel.org/r/0-v1-c773ecb137bc+11f-hns_gcc8_jgg@nvidia.com
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/infiniband/hw/hns/hns_roce_hw_v2.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/hns/hns_roce_hw_v2.c b/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
index c320891c8763..6cb4a4e10837 100644
--- a/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
+++ b/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
@@ -4411,7 +4411,12 @@ static int modify_qp_init_to_rtr(struct ib_qp *ibqp,
hr_qp->path_mtu = ib_mtu;

mtu = ib_mtu_enum_to_int(ib_mtu);
- if (WARN_ON(mtu < 0))
+ if (WARN_ON(mtu <= 0))
+ return -EINVAL;
+#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 / mtu);
+ if (WARN_ON(lp_pktn_ini >= 0xF))
return -EINVAL;

if (attr_mask & IB_QP_PATH_MTU) {
@@ -4419,10 +4424,6 @@ static int modify_qp_init_to_rtr(struct ib_qp *ibqp,
hr_reg_clear(qpc_mask, QPC_MTU);
}

-#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 / mtu);
-
hr_reg_write(context, QPC_LP_PKTN_INI, lp_pktn_ini);
hr_reg_clear(qpc_mask, QPC_LP_PKTN_INI);

--
2.33.0