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RAS/AMD/ATL: Replace bitwise_xor_bits() with hweight16() 

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 hweight16(),
the resulting code boils down to 2 instructions -  POPCNT and AND, and all
relevant CPUs support POPCNT.

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.

No functional changes.

  [ bp: Massage commit message. ]

Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251124142517.1708451-1-nik.borisov@suse.com
This commit is contained in:
Nikolay Borisov 2025-11-24 16:25:17 +02:00 committed by Borislav Petkov (AMD)
parent 187d1b27a1
commit 69acbdbbef
1 changed files with 5 additions and 16 deletions
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21
drivers/ras/amd/atl/umc.c
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@ -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;
}