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    Subject[PATCH v2 01/24] EDAC, mc: Fix grain_bits calculation
    Date
    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@marvell.com>
    ---
    drivers/edac/edac_mc.c | 10 ++++++++--
    1 file changed, 8 insertions(+), 2 deletions(-)

    diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
    index 64922c8fa7e3..45cac74ab833 100644
    --- a/drivers/edac/edac_mc.c
    +++ b/drivers/edac/edac_mc.c
    @@ -1235,9 +1235,15 @@ 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;
    + /*
    + * We expect the hw to report a reasonable grain, fallback to
    + * 1 byte granularity otherwise.
    + */
    + 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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