linux-kernel - Re: [PATCH] m68k: Implement ndelay() as an inline function to force type checking/casting

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Date:   Mon, 14 May 2018 12:52:33 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michael Schmitz <schmitzmic@...il.com>
Subject: Re: [PATCH] m68k: Implement ndelay() as an inline function to force
 type checking/casting

Hi Boris,

On Mon, May 14, 2018 at 11:29 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Sun, May 13, 2018 at 4:02 PM, Boris Brezillon
> <boris.brezillon@...tlin.com> wrote:
>> ndelay() is supposed to take an unsigned long, but if you define
>> ndelay() as a macro and the caller pass an unsigned long long instead
>> of an unsigned long, the unsigned long long to unsigned long cast is
>> not done and we end up with an "undefined reference to `__udivdi3'"
>> error at link time.
>>
>> Fix that by making ndelay() an inline function and then defining dummy
>> ndelay() macro that redirects to the ndelay() function (it's how most
>> archs do to implement ndelay()).
>>
>> Fixes: c8ee038bd148 ("m68k: Implement ndelay() based on the existing udelay() logic")
>> Signed-off-by: Boris Brezillon <boris.brezillon@...tlin.com>
>> ---
>> Hello Geert,
>>
>> This patch is fixing the bug reported by kbuild test robot here [1].
>> I could have patched the PSEC_TO_NSEC() macro to cast the result of
>> the division on a u32, but I thought making m68k consistent with what
>> other archs do would be preferable.
>>
>> Let me know if don't like the solution, and I'll patch the ndelay()
>> caller instead.
>
> Thanks for your patch!
>
> With the comment a few lines above removed:
>
>     - * This is a macro so that the const version can factor out the first
>     - * multiply and shift.
>
> Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>

I've just posted a fix for the root cause ("[PATCH] mtd: nand: Fix return
type of __DIVIDE() when called with 32-bit",
https://lkml.org/lkml/2018/5/14/578), so the fix for m68k's ndelay() is not
that urgent anymore.

As your patch is still a valid fix, I'll apply it, and queue it up for v4.18.

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds