linux-kernel - Re: [PATCH] staging: pi433: use div

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Date:   Fri, 28 Jul 2017 16:21:05 +0200 (CEST)
From:   Marcus Wolf <marcus.wolf@...f-entwicklungen.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: Re: [PATCH] staging: pi433: use div_u64 for 64-bit division

Hi Arnd,

we already have a patch for this: 
[PATCH 1/1] staging: pi433: fix problem with division in rf69_set_deviation
 from 20.07.2017

Maybe I did something wrong, but my first solution was exactly like your
proposal. As far as I remeber, I wasn't able to compile it that way. Therefore I
made a little bit more complicated fix. If I did something wrong and yours is
fine, we should go for yours, because it is a shorter solution.

Thanks,

Marcus

> Arnd Bergmann <arnd@...db.de> hat am 28. Juli 2017 um 15:23 geschrieben:
>
>
> I ran into this link error on an ARM OABI build:
>
> drivers/staging/pi433/rf69.o: In function `rf69_set_frequency':
> rf69.c:(.text+0xc9c): undefined reference to `__udivdi3'
>
> No idea why I didn't see it with the default EABI configurations,
> but the right solution here seems to be to use div_u64()
> to get the external division implementation.
>
> Fixes: 874bcba65f9a ("staging: pi433: New driver")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> drivers/staging/pi433/rf69.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/pi433/rf69.c b/drivers/staging/pi433/rf69.c
> index e391ce777bc7..e5267b5638c0 100644
> --- a/drivers/staging/pi433/rf69.c
> +++ b/drivers/staging/pi433/rf69.c
> @@ -238,7 +238,7 @@ int rf69_set_frequency(struct spi_device *spi, u32
> frequency)
> do_div(f_step, 524288); // 524288 = 2^19
>
> // check input value
> - f_max = f_step * 8388608 / factor;
> + f_max = div_u64(f_step * 8388608, factor);
> if (frequency > f_max)
> {
> dev_dbg(&spi->dev, "setFrequency: illegal input param");
> --
> 2.9.0
>
>