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SubjectRe: [PATCH] mtd: ubi: avoid expensive do_div() on 32-bit machines
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在 2024/3/13 16:46, Arnd Bergmann 写道:
> From: Arnd Bergmann <arnd@arndb.de>
>
> The use of do_div() in ubi_nvmem_reg_read() makes calling it on
> 32-bit machines rather expensive. Since the 'from' variable is
> known to be a 32-bit quantity, it is clearly never needed and
> can be optimized into a regular division operation.
>
> Fixes: b8a77b9a5f9c ("mtd: ubi: fix NVMEM over UBI volumes on 32-bit systems")
> Fixes: 3ce485803da1 ("mtd: ubi: provide NVMEM layer over UBI volumes")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/mtd/ubi/nvmem.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
>
> diff --git a/drivers/mtd/ubi/nvmem.c b/drivers/mtd/ubi/nvmem.c
> index 8aeb9c428e51..a94a1a9aaec1 100644
> --- a/drivers/mtd/ubi/nvmem.c
> +++ b/drivers/mtd/ubi/nvmem.c
> @@ -6,7 +6,6 @@
> /* UBI NVMEM provider */
> #include "ubi.h"
> #include <linux/nvmem-provider.h>
> -#include <asm/div64.h>
>
> /* List of all NVMEM devices */
> static LIST_HEAD(nvmem_devices);
> @@ -27,14 +26,15 @@ static int ubi_nvmem_reg_read(void *priv, unsigned int from,
> struct ubi_nvmem *unv = priv;
> struct ubi_volume_desc *desc;
> uint32_t offs;
> - uint64_t lnum = from;
> + uint32_t lnum;
> int err = 0;
>
> desc = ubi_open_volume(unv->ubi_num, unv->vol_id, UBI_READONLY);
> if (IS_ERR(desc))
> return PTR_ERR(desc);
>
> - offs = do_div(lnum, unv->usable_leb_size);
> + offs = from % unv->usable_leb_size;
> + lnum = from / unv->usable_leb_size;
> while (bytes_left) {
> to_read = unv->usable_leb_size - offs;
>
>


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