Re: [PATCH 1/4] bitops: Introduce assign_bit()

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Aug 21, 2017 at 3:12 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote:

> A common idiom is to assign a value to a bit with:
>
>     if (value)
>         set_bit(nr, addr);
>     else
>         clear_bit(nr, addr);
>
> Likewise common is the one-line expression variant:
>
>     value ? set_bit(nr, addr) : clear_bit(nr, addr);
>
> Commit 9a8ac3ae682e ("dm mpath: cleanup QUEUE_IF_NO_PATH bit
> manipulation by introducing assign_bit()") introduced assign_bit()
> to the md subsystem for brevity.
>
> Make it available to others, in particular gpiolib and the upcoming
> driver for Maxim MAX3191x industrial serializer chips.
>
> Cc: Bart Van Assche <bart.vanassche@xxxxxxx>
> Cc: Alasdair Kergon <agk@xxxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>

Looks reasonable.

> +static __always_inline void assign_bit(bool value, long nr,
> +                                      volatile unsigned long *addr)
> +{
> +       if (value)
> +               set_bit(nr, addr);
> +       else
> +               clear_bit(nr, addr);
> +}
> +
> +static __always_inline void __assign_bit(bool value, long nr,
> +                                        volatile unsigned long *addr)
> +{
> +       if (value)
> +               __set_bit(nr, addr);
> +       else
> +               __clear_bit(nr, addr);
> +}

What I have never understood is the semantic difference between
bitop_foo() and __bitop_foo().

And I even use them quite a lot.

Can someone explain when I use the bitop_foo() and when I
use the __bitop_foo(). I am asking so I can understand patch
2/4 in this series.

I guess this is why I generally detest the __annotation, since it is
so unspecific and unclear, but that is not something I expect you
to solve in this patch.

Yours,
Linus Walleij
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