• FUJITA Tomonori's avatar
    uml: define CONFIG_NO_DMA · d911202e
    FUJITA Tomonori authored
    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: default avatarFUJITA 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: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    d911202e
Kconfig.um 5.1 KB