Re: [PATCH] mtd: spi-nor: replace unnecessary div64_u64() with div_u64()

Michael Walle
2024-04-29T13:47:36Z

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Hi,

On Mon Apr 29, 2024 at 3:27 PM CEST, Pratyush Yadav wrote:
> On Mon, Apr 29 2024, Michael Walle wrote:
>
> > Both occurences of div64_u64() just have a u8 or u32 divisor. Use
> > div_u64() instead.
>
> Does this improve performance or is this only for correctness?

See function doc for div_u64():

* This is the most common 64bit divide and should be used if possible,
* as many 32bit archs can optimize this variant better than a full 64bit
* divide.

> Patch LGTM otherwise.
>
> Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
>
> BTW, I also noticed that there is a do_div() call in spi_nor_write()
> that also uses a u64 dividend and u32 divisor. I was wondering why it
> uses do_div() and not div_u64() (I am not sure what the difference
> between the two is) but I suppose it doesn't matter much since your
> spring cleaning series will delete that code anyway.

do_div() is a macro and is modifying the dividend in place, whereas
div_u64() will return it. do_div() is using u32 for the divisor
anyway.

-michael

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