Commit 69acbdbb authored by Nikolay Borisov's avatar Nikolay Borisov Committed by Borislav Petkov (AMD)
Browse files

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: default avatarNikolay Borisov <nik.borisov@suse.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251124142517.1708451-1-nik.borisov@suse.com
parent 187d1b27

drivers/ras/amd/atl/umc.c

+5 −16
Original line number Diff line number Diff line
@@ -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;

	}