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    Subject[PATCH 4.16 265/279] mtd: rawnand: Fix return type of __DIVIDE() when called with 32-bit
    Date
    4.16-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Geert Uytterhoeven <geert@linux-m68k.org>

    [ Upstream commit 9f825e74d761c13b0cfaa5f65344d64ff970e252 ]

    The __DIVIDE() macro checks whether it is called with a 32-bit or 64-bit
    dividend, to select the appropriate divide-and-round-up routine.
    As the check uses the ternary operator, the result will always be
    promoted to a type that can hold both results, i.e. unsigned long long.

    When using this result in a division on a 32-bit system, this may lead
    to link errors like:

    ERROR: "__udivdi3" [drivers/mtd/nand/raw/nand.ko] undefined!

    Fix this by casting the result of the division to the type of the
    dividend.

    Fixes: 8878b126df769831 ("mtd: nand: add ->exec_op() implementation")
    Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
    Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    include/linux/mtd/rawnand.h | 16 +++++++++++-----
    1 file changed, 11 insertions(+), 5 deletions(-)

    --- a/include/linux/mtd/rawnand.h
    +++ b/include/linux/mtd/rawnand.h
    @@ -824,12 +824,18 @@ struct nand_op_instr {
    * tBERS (during an erase) which all of them are u64 values that cannot be
    * divided by usual kernel macros and must be handled with the special
    * DIV_ROUND_UP_ULL() macro.
    + *
    + * Cast to type of dividend is needed here to guarantee that the result won't
    + * be an unsigned long long when the dividend is an unsigned long (or smaller),
    + * which is what the compiler does when it sees ternary operator with 2
    + * different return types (picks the largest type to make sure there's no
    + * loss).
    */
    -#define __DIVIDE(dividend, divisor) ({ \
    - sizeof(dividend) == sizeof(u32) ? \
    - DIV_ROUND_UP(dividend, divisor) : \
    - DIV_ROUND_UP_ULL(dividend, divisor); \
    - })
    +#define __DIVIDE(dividend, divisor) ({ \
    + (__typeof__(dividend))(sizeof(dividend) <= sizeof(unsigned long) ? \
    + DIV_ROUND_UP(dividend, divisor) : \
    + DIV_ROUND_UP_ULL(dividend, divisor)); \
    + })
    #define PSEC_TO_NSEC(x) __DIVIDE(x, 1000)
    #define PSEC_TO_MSEC(x) __DIVIDE(x, 1000000000)


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