linux-kernel - Re: [PATCH] bitops: add equivalent of BIT(x) for bitfields

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Date:   Mon, 5 Dec 2016 18:47:38 +0100
From:   Sebastian Frias <sf84@...oste.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     zijun_hu <zijun_hu@....com>, Sasha Levin <sasha.levin@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mason <slash.tmp@...e.fr>,
        Maxime Coquelin <maxime.coquelin@...com>,
        Harvey Harrison <harvey.harrison@...il.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] bitops: add equivalent of BIT(x) for bitfields

On 05/12/16 18:13, Linus Torvalds wrote:
> On Mon, Dec 5, 2016 at 5:36 AM, Sebastian Frias <sf84@...oste.net> wrote:
>> Introduce SETBITFIELD(msb, lsb, value) macro to ease dealing with
>> continuous bitfields, just as BIT(x) does for single bits.
>>
>> SETBITFIELD_ULL(msb, lsb, value) macro is also added.
> 
> No. No, no, no.
> 
> Didn't we have this discussion already? Or was that for one of the
> other silly naming things?
> 
> That thing doesn't "SET" anything at all. It generates a value, nothing more.
> 
> So the name is completely unacceptable. It follows the convention of
> GENMASK, so maybe GENVALUE?
> 

Thanks for your input.
I was looking for suggestions on the name, thanks for yours, I will submit
a v2 with the name changed as you proposed.

> I also absolutely hate the stupid "big bit first" idiocy, but we did
> that for GENMASK too, so I guess we're stuck with that retarded model.
> 

Yes, I followed the same convention.

> Yes, I understand why it happened - people look at register definition
> graphics, and the high bits are to the left.
> 
> But when you then read the documentation, it will still say things
> like "bits 9 through 12 contain the value XYZ", because while
> individual numbers are written MSB first, we actuall _read_ left to
> right. You'd never give a range as "12 to 5", you'd say "5 to 12".
> 
>            Linus
>