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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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