I think that it's better to detect DMA misuse at build time rather than
calling BUG_ON. Architectures that can't do DMA need to define
CONFIG_NO_DMA.
Thanks to Sam Ravnborg for explaining how CONFIG_NO_DMA and CONFIG_HAS_DMA
work:
http://marc.info/?l=linux-kernel&m=128359913825550&w=2
HAS_DMA is defined like this:
config HAS_DMA
boolean
depends on !NO_DMA
default y
So to set HAS_DMA to true an arch should do:
1) Do not define NO_DMA
2) Define NO_DMA abd set it to 'n'
Must archs - including um - used principle 1).
In the um case we want to say that we do NOT have any DMA.
This can be done in two ways.
a) define NO_DMA and set it to 'y'
b) redefine HAS_DMA and set it to 'n'.
The patch you provided used principle b) where other archs use principle a).
So I suggest you should use principle a) for um too.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
d911202e3f