1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
index f272247d1708..d4bf0e694541 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
@@ -328,7 +328,18 @@ __emit_shf(struct nfp_prog *nfp_prog, u16 dst, enum alu_dst_ab dst_ab,
                 return;
         }
 
-        if (sc == SHF_SC_L_SHF)
+        /* NFP shift instruction has something special. If shift direction is
+         * left then shift amount of 1 to 31 is specified as 32 minus the amount
+         * to shift.
+         *
+         * But no need to do this for indirect shift which has shift amount be
+         * 0. Even after we do this subtraction, shift amount 0 will be turned
+         * into 32 which will eventually be encoded the same as 0 because only
+         * low 5 bits are encoded, but shift amount be 32 will fail the
+         * FIELD_PREP check done later on shift mask (0x1f), due to 32 is out of
+         * mask range.
+         */
+        if (sc == SHF_SC_L_SHF && shift)
                 shift = 32 - shift;
 
         insn = OP_SHF_BASE |