Re: [PATCH 1 of 3] Introduce __memcpy_toio32

[Adrian Bunk]

On Fri, Dec 30, 2005 at 04:23:46PM -0800, Linus Torvalds wrote:
>...
> > > Where's the problem with the __HAVE_ARCH_* mechanism?
>...
> And no, I don't like the __HAVE_ARCH_xxx mechanisms at all. They are 
> pointless, and hard to follow. If an architecture wants to use a generic 
> mechanism, it should do one of the following (or a combination):
> 
>  - use the config file mechanism, and use
> 
> 	obj-$(CONFIG_GENERIC_FOO) += generic-foo.c
> 
>    in a Makefile to link in the generic version.
> 
>    Examples: CONFIG_RWSEM_GENERIC_SPINLOCK.
> 
>  - just include the generic header from its own header, eg just do a
> 
> 	#include <asm-generic/div64.h>
> 
>    or similar.
> 
> Now, the latter in particular is very easy to follow: if you look into the 
> <asm/div64.h> file and see that it just includes <asm-generic/div64.h>, 
> it's very obvious what is going on and where to find the real 
> implementation. You never have to wonder what the indirection means. 
>...
> Now, the CONFIG_GENERIC_FOO thing is a bit less obvious, and you may have 
> to know about that config option in order to realize that a particular 
> architecture is using a generic library routine, but at least with those 
> Kconfig options, the language to describe them is clean these days, and 
> it's _the_ standard way to express configuration information. So it may be 
> a bit subtler and more indirect, but once you get used to it, it too is 
> very clean.
>...

OK, this I don't have any problem with.

I'm not yet fully convinced that __HAVE_ARCH_xxx is really that bad, but 
your proposed solution doesn't have the problems I had in mind.

What is OK:
  obj-$(CONFIG_GENERIC_FOO) += generic-foo.o

What is not OK:
  lib-y += generic-foo.o

The latter has the following disadvantages:
- it's non-obvious whether the object actually gets included in the 
  kernel
- if the contents of generic-foo.o is only used in modules, 
  generic-foo.o is _not_ included in the kernel resulting in an
  obvious breakage

> 			Linus

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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