Messages in this thread Patch in this message |  | | From | Nikolay Borisov <> | | Subject | [PATCH] RAS/AMD/ATL: Replace bitwise_xor_bits() with hweight16() | | Date | Mon, 24 Nov 2025 16:25:17 +0200 |
| |
Doing hweight16 and checking whether the lsb is set is functionally equivalent to what bitwise_xor_bits() does. In addition it results in better generated code as before gcc would inline the function 4 times. With hweight, the resulting code boils down to 2 instructions - popcnt and andl as all cpus we care about has popcnt. No functional changes.
An alternative would have been to use the __builtin_parity() function provided by both Clang/GCC, however under some circumstances the compiler can choose not to inline it but generate a library call which is unsupported in the kernel.
Signed-off-by: Nikolay Borisov <nik.borisov@suse.com> --- drivers/ras/amd/atl/umc.c | 21 +++++---------------- 1 file changed, 5 insertions(+), 16 deletions(-)
diff --git a/drivers/ras/amd/atl/umc.c b/drivers/ras/amd/atl/umc.c index 6e072b7667e9..8d1363237eee 100644 --- a/drivers/ras/amd/atl/umc.c +++ b/drivers/ras/amd/atl/umc.c @@ -49,17 +49,6 @@ static u8 get_coh_st_inst_id_mi300(struct atl_err *err) return i; }
-/* XOR the bits in @val. */ -static u16 bitwise_xor_bits(u16 val) -{ - u16 tmp = 0; - u8 i; - - for (i = 0; i < 16; i++) - tmp ^= (val >> i) & 0x1; - - return tmp; -}
struct xor_bits { bool xor_enable; @@ -250,17 +239,17 @@ static unsigned long convert_dram_to_norm_addr_mi300(unsigned long addr) if (!addr_hash.bank[i].xor_enable) continue;
- temp = bitwise_xor_bits(col & addr_hash.bank[i].col_xor); - temp ^= bitwise_xor_bits(row & addr_hash.bank[i].row_xor); + temp = hweight16(col & addr_hash.bank[i].col_xor) & 1; + temp ^= hweight16(row & addr_hash.bank[i].row_xor) & 1; bank ^= temp << i; }
/* Calculate hash for PC bit. */ if (addr_hash.pc.xor_enable) { - temp = bitwise_xor_bits(col & addr_hash.pc.col_xor); - temp ^= bitwise_xor_bits(row & addr_hash.pc.row_xor); + temp = hweight16(col & addr_hash.pc.col_xor) & 1; + temp ^= hweight16(row & addr_hash.pc.row_xor) & 1; /* Bits SID[1:0] act as Bank[5:4] for PC hash, so apply them here. */ - temp ^= bitwise_xor_bits((bank | sid << NUM_BANK_BITS) & addr_hash.bank_xor); + temp ^= hweight16((bank | sid << NUM_BANK_BITS) & addr_hash.bank_xor) & 1; pc ^= temp; }
-- 2.52.0
|  |