On Tue, Aug 27, 2013 at 9:16 PM, Felipe Balbi <balbi@xxxxxx> wrote:
> On Mon, Aug 19, 2013 at 09:24:01AM +0800, Peter Chen wrote:
>> On Sun, Aug 18, 2013 at 10:20:44PM +0200, Geert Uytterhoeven wrote:
>> > If NO_DMA=y:
>> >
>> > drivers/built-in.o: In function `dma_set_coherent_mask':
>> > include/linux/dma-mapping.h:93: undefined reference to `dma_supported'
>> >
>> > Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
>> > ---
>> > drivers/usb/chipidea/Kconfig | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/usb/chipidea/Kconfig b/drivers/usb/chipidea/Kconfig
>> > index d1bd8ef..dbd5232 100644
>> > --- a/drivers/usb/chipidea/Kconfig
>> > +++ b/drivers/usb/chipidea/Kconfig
>> > @@ -1,6 +1,6 @@
>> > config USB_CHIPIDEA
>> > tristate "ChipIdea Highspeed Dual Role Controller"
>> > - depends on USB || USB_GADGET
>> > + depends on (USB || USB_GADGET) && HAS_DMA
>> > help
>> > Say Y here if your system has a dual role high speed USB
>> > controller based on ChipIdea silicon IP. Currently, only the
>>
>> I can't understand why the DMA can't be changed to fix this instead
>> of changing every driver?
>
> I'm with you. It'd be nicer to just provide empty stubs when !HAS_DMA
That would give us drivers that compile but don't work.
Not having stubs is intentional, cfr. the comment at the top of
include/asm-generic/dma-mapping-broken.h:
/* define the dma api to allow compilation but not linking of
* dma dependent code. Code that depends on the dma-mapping
* API needs to set 'depends on HAS_DMA' in its Kconfig
*/
and the comments in the commit that introduced it:
commit 1b0fac45878bb88759eec347c273285195649ff7
Author: Dan Williams <dan.j.williams@xxxxxxxxx>
Date: Sun Jul 15 23:40:26 2007 -0700
dma-mapping: prevent dma dependent code from linking on !HAS_DMA archs
Continuing the work started in 411f0f3edc141a582190d3605cadd1d993abb6df ...
This enables code with a dma path, that compiles away, to build without
requiring additional code factoring. It also prevents code that calls
dma_alloc_coherent and dma_free_coherent from linking whereas previously
the code would hit a BUG() at run time. Finally, it allows archs that set
!HAS_DMA to delete their asm/dma-mapping.h file.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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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