Re: [PATCH] asm-generic: add a dma-mapping.h file
From: FUJITA Tomonori
Date: Tue May 26 2009 - 23:59:20 EST
On Tue, 26 May 2009 13:35:41 +0100
Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Tuesday 26 May 2009, FUJITA Tomonori wrote:
> > > dma_get_cache_alignment() is still less generic than
> > > the other functions, as this is still architecture
> > > specific. Should I leave that out as well then?
> > Yes, I think that only adding generic functions is a better
> > approach. Overriding with #ifdef is really ugly.
> Ok, will do.
> [trimming Cc list a bit, as the subject has changed]
> Could you be more specific as to why you think the #ifdef
> in this file is ugly? I agree that we should always avoid
> #ifdef in a device driver file or around the usage of an
> API, but we use it everywhere when defining an optional
Seems that people think regard #ifdef in *.c bad, I think.
> API, e.g.
> #ifdef CONFIG_DMA_API_DEBUG
> extern void dma_debug_add_bus(struct bus_type *bus);
> static inline void dma_debug_add_bus(struct bus_type *bus)
This example is inappropriate; a different way to use #ifdef.
This just ensures that dma_debug_add_bus() is available even if
CONFIG_DMA_API_DEBUG is disabled.
It's completely different from a way how you use #ifdef.
> #ifndef clear_user_highpage
> static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
> void *addr = kmap_atomic(page, KM_USER0);
> clear_user_page(addr, vaddr, page);
> kunmap_atomic(addr, KM_USER0);
#define clear_user_highpage(page,vaddr) \
Personally, I don't fancy this style but it's a matter of taste, I
> This has always made a lot of sense to me when you are defining
> something that you want to become a No-op in certain configurations
> or that only needs special handling in a few cases. IIRC, Linus
> has stated that he prefers the second of the two styles above when
> you have the choice, which is why I started out that way, while
> for the dma_debug stuff, the CONFIG_ symbol clearly makes sense.
> Arnd <><
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