Re: [PATCH 1/2] asm-generic: io: remove {read,write} string functions

Will Deacon
2012-05-01T13:35:24Z

On Sat, Apr 28, 2012 at 12:26:11AM +0100, Mike Frysinger wrote:
> On Friday 27 April 2012 16:52:34 Arnd Bergmann wrote:
> > The main reasons I can see for not making it a general purpose API are:
> >
> > * It's a very confusing interface, because the endianess rules are
> > different from the non-string variants and counterintuitive.
> >
> > * Almost all the users are ancient ARM specific drivers, the others are
> > either new ARM specific drivers or drivers that started out as ARM-only
> > and were ported later to other architectures (sh, avr32, mips, mn10300
> > and blackfin)
> >
> > * On all these architectures, the PCI I/O space is memory mapped (or
> > non-existent), so the ioread* functions are trivial wrappers without
> > additional overhead.
> >
> > * Most architectures don't implement them today, but all architectures
> > that support MMIO also implement the ioread string operations.
>
> i'm ambivalent with keeping or tossing these funcs. Blackfin (afaik) picked
> them up really only for the reasons Arnd cited -- drivers using memory mapped
> registers originally for ARM (or m68k/coldfire i think) used this API, and it
> was easier for us to implement these defines in our asm/io.h and get the
> drivers "for free".

Makes sense and there's no compelling reason to convert drivers if they're
not being used by architectures without these functions.

> i am strongly in favor though of agreeing on & documenting the baseline API
> first before attempting to clean anything up. sorry to keep harping on this.

It would be nice if we could just use asm-generic/io.h as the documention,
i.e. if you want to write a portable driver, just stick to the functions
implemented there. Apart from the string accessors, I think it's already
fairly accurate. The __raw_* functions seem to be missing on s390 but I
don't think driver portability is a huge concern for that architecture.

Will