[PATCH 01/17] bitfield: Add non-constant field_{prep,get}() helpers
From: Johannes Berg <johannes@sipsolutions.net>
Date: 2021-11-22 16:34:44
Also in:
alsa-devel, linux-clk, linux-gpio, linux-iio, linux-media, linux-mmc, linux-omap, linux-pm, linux-renesas-soc, linux-wireless, lkml, netdev
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