• Christoph Lameter's avatar
    [PATCH] Set CONFIG_ZONE_DMA for arches with GENERIC_ISA_DMA · 5ac6da66
    Christoph Lameter authored
    As Andi pointed out: CONFIG_GENERIC_ISA_DMA only disables the ISA DMA
    channel management.  Other functionality may still expect GFP_DMA to
    provide memory below 16M.  So we need to make sure that CONFIG_ZONE_DMA is
    set independent of CONFIG_GENERIC_ISA_DMA.  Undo the modifications to
    mm/Kconfig where we made ZONE_DMA dependent on GENERIC_ISA_DMA and set
    theses explicitly in each arches Kconfig.
    Reviews must occur for each arch in order to determine if ZONE_DMA can be
    switched off.  It can only be switched off if we know that all devices
    supported by a platform are capable of performing DMA transfers to all of
    memory (Some arches already support this: uml, avr32, sh sh64, parisc and
    In order to switch ZONE_DMA off conditionally, one would have to establish
    a scheme by which one can assure that no drivers are enabled that are only
    capable of doing I/O to a part of memory, or one needs to provide an
    alternate means of performing an allocation from a specific range of memory
    (like provided by alloc_pages_range()) and insure that all drivers use that
    call.  In that case the arches alloc_dma_coherent() may need to be modified
    to call alloc_pages_range() instead of relying on GFP_DMA.
    Signed-off-by: default avatarChristoph Lameter <clameter@sgi.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Kconfig 41.2 KB