linux-kernel - Re: [PATCH] RAS/AMD/ATL: Replace bitwise_xor

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Message-ID: <20251124170257.GHaSSPwe1nDUQgI5MQ@fat_crate.local>
Date: Mon, 24 Nov 2025 18:02:57 +0100
From: Borislav Petkov <bp@...en8.de>
To: Nikolay Borisov <nik.borisov@...e.com>
Cc: linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
	Yazen.Ghannam@....com
Subject: Re: [PATCH] RAS/AMD/ATL: Replace bitwise_xor_bits() with hweight16()

On Mon, Nov 24, 2025 at 04:25:17PM +0200, Nikolay Borisov wrote:
> 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@...e.com>
> ---
>  drivers/ras/amd/atl/umc.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)

Applied, thanks.

-- 
Regards/Gruss,
    Boris.

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