Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Tue, 23 Nov 2021 09:20:23 +0100 | Subject | Re: [PATCH 00/17] Non-const bitfield helper conversions |
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Hi Alexandre,
On Mon, Nov 22, 2021 at 6:50 PM Alexandre Belloni <alexandre.belloni@bootlin.com> wrote: > On 22/11/2021 16:53:53+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. > > To avoid this limitation, the AT91 clock driver already has its own > > field_{prep,get}() macros. > > My understanding was that this (being compile time only) was actually > done on purpose. Did I misunderstand?
Yes, it was done on purpose, to maximize type safety.
However, this imposes a severe limitation: we cannot use them in case the mask is non-const (i.e. stored in some data structure). This is a quite common use-case, given the examples I found and converted, and given you added field_{get,prep}() to the AT91 clock driver.
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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
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