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From:   Robert Richter <rrichter@marvell.com>
To:     James Morse <james.morse@arm.com>
CC:     Borislav Petkov <bp@alien8.de>, Tony Luck <tony.luck@intel.com>,
        "Mauro Carvalho Chehab" <mchehab@kernel.org>,
        "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 11/21] EDAC, ghes: Unify trace_mc_event() code with
 edac_mc driver
Thread-Topic: [PATCH 11/21] EDAC, ghes: Unify trace_mc_event() code with
 edac_mc driver
Thread-Index: AQHVIjaakgBofopjtEaC8Krw4A3kQQ==
Date:   Thu, 13 Jun 2019 22:23:18 +0000
Message-ID: <20190613222305.eqvpom2bgcavq5it@rric.localdomain>
References: <20190529084344.28562-1-rrichter@marvell.com>
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 <37d47356-a40b-2739-10df-f5ab83fa2b36@arm.com>
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On 04.06.19 18:15:50, James Morse wrote:
> On 03/06/2019 14:10, Robert Richter wrote:
> > The +1 looks odd to me also for the edac_mc driver, but I need to take
> > a closer look here as well as some logs suggest the grain is
> > calculated correctly.
>=20
> My theory on this is that ghes_edac.c is generating a grain like 0x1000, =
fls() does the
> right thing. Other edac drivers are generating a grain like 0xfff to desc=
ribe the same
> size, fls() is now off-by-one, hence the addition.
> I don't have a platform where I can trigger any other edac driver to test=
 this though.
>=20
> The way round this would be to put the grain_bits in struct edac_raw_erro=
r_desc so that
> ghes_edac.c can calculate it directly.

I think the grain calculation in edac_mc is broken from the beginning:

 53f2d0289875 RAS: Add a tracepoint for reporting memory controller events

The log we see in the patch desc is:

 mc_event: 1 Corrected error:memory read on memory stick DIMM_1A (mc:0 loca=
tion:0:0:0 page:0x586b6e offset:0xa66 grain:32 syndrome:0x0 area:DMA)

The grain reported in mc_event there is probably 8 (quad word,
granularity in bytes) and calculates as follows:

 dimm->grain =3D 8
 e->grain =3D dimm->grain
 grain_bits =3D fls_long(e->grain) + 1 =3D 4 + 1 =3D 5
 __entry->grain_bits =3D grain_bits
 TP_printk() =3D 1 << __entry->grain_bits =3D 2 << 5 =3D 32

So the reported grain of 32 should actually be 8.

I think the following is correct:

 grain_bits =3D fls_long(e->grain ? e->grain - 1 : 0);

This also handles the case if e->grain is not a power of 2.

Thoughts?

-Robert