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Subject[PATCH 5.3 072/344] EDAC/mc: Fix grain_bits calculation
Date
From: Robert Richter <rrichter@marvell.com>

[ Upstream commit 3724ace582d9f675134985727fd5e9811f23c059 ]

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

Replace 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(7)
grain_bits = 3

grain = 1 << 3 = 8

Also, check if the hardware reports a reasonable grain != 0 and fallback
with a warning to 1 byte granularity otherwise.

[ bp: massage a bit. ]

Signed-off-by: Robert Richter <rrichter@marvell.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20190624150758.6695-2-rrichter@marvell.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/edac/edac_mc.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
index 64922c8fa7e3b..d899d86897d06 100644
--- a/drivers/edac/edac_mc.c
+++ b/drivers/edac/edac_mc.c
@@ -1235,9 +1235,13 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
if (p > e->location)
*(p - 1) = '\0';

- /* Report the error via the trace interface */
- grain_bits = fls_long(e->grain) + 1;
+ /* Sanity-check driver-supplied grain value. */
+ if (WARN_ON_ONCE(!e->grain))
+ e->grain = 1;
+
+ grain_bits = fls_long(e->grain - 1);

+ /* Report the error via the trace interface */
if (IS_ENABLED(CONFIG_RAS))
trace_mc_event(type, e->msg, e->label, e->error_count,
mci->mc_idx, e->top_layer, e->mid_layer,
--
2.20.1


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