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Message-ID: <01b44b38c087c151171f8d45a2090474c2559306.camel@sipsolutions.net>
Subject: Re: [PATCH 01/17] bitfield: Add non-constant field_{prep,get}()
 helpers
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Geert Uytterhoeven <geert+renesas@glider.be>,
        Tony Lindgren <tony@atomide.com>,
        Russell King <linux@armlinux.org.uk>,
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Date:   Mon, 22 Nov 2021 17:32:43 +0100
In-Reply-To: <3a54a6703879d10f08cf0275a2a69297ebd2b1d4.1637592133.git.geert+renesas@glider.be>
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On Mon, 2021-11-22 at 16:53 +0100, Geert Uytterhoeven wrote:
> The existing FIELD_{GET,PREP}() macros are limited to compile-time
> constants.  However, it is very common to prepare or extract bitfield
> elements where the bitfield mask is not a compile-time constant.
> 

I'm not sure it's really a good idea to add a third API here?

We have the upper-case (constant) versions, and already
{u32,...}_get_bits()/etc.

Also, you're using __ffs(), which doesn't work for 64-bit on 32-bit
architectures (afaict), so that seems a bit awkward.

Maybe we can make {u32,...}_get_bits() be doing compile-time only checks
if it is indeed a constant? The __field_overflow() usage is already only
done if __builtin_constant_p(v), so I guess we can do the same with
__bad_mask()?

johannes