linux-kernel - Re: [PATCH v2 01/24] EDAC, mc: Fix grain

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Date:   Sat, 3 Aug 2019 12:08:37 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Robert Richter <rrichter@...vell.com>
Cc:     James Morse <james.morse@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 01/24] EDAC, mc: Fix grain_bits calculation

On Mon, Jun 24, 2019 at 03:08:55PM +0000, Robert Richter wrote:
> The grain in edac is defined as "minimum granularity for an error
> report, in bytes". The following calculation of the grain_bits in
> edac_mc is wrong:
> 
> 	grain_bits = fls_long(e->grain) + 1;
> 
> Where grain_bits is defined as:
> 
> 	grain = 1 << grain_bits
> 
> Example:
> 
> 	grain = 8	# 64 bit (8 bytes)
> 	grain_bits = fls_long(8) + 1
> 	grain_bits = 4 + 1 = 5
> 
> 	grain = 1 << grain_bits
> 	grain = 1 << 5 = 32
> 
> Replacing it with the correct calculation:
> 
> 	grain_bits = fls_long(e->grain - 1);
> 
> The example gives now:
> 
> 	grain_bits = fls_long(8 - 1)
> 	grain_bits = fls_long(8 - 1)
> 	grain_bits = 3
> 
> 	grain = 1 << 3 = 8
> 
> Note: We need to check if the hardware reports a reasonable grain != 0
> and fallback with a warn_once and 1 byte granularity otherwise.
> 
> Signed-off-by: Robert Richter <rrichter@...vell.com>
> ---
>  drivers/edac/edac_mc.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

Applied to the new EDAC repo:

https://git.kernel.org/pub/scm/linux/kernel/git/ras/ras.git/log/?h=edac-for-next

Thx.

-- 
Regards/Gruss,
    Boris.

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