Re: [PATCH 2/6] Introduce CONFIG_ZONE_DMA

Paul Mundt
2006-09-18T15:22:43Z

On Mon, Sep 18, 2006 at 02:55:59PM +0100, Christoph Hellwig wrote:
> On Mon, Sep 11, 2006 at 03:27:39PM -0700, Christoph Lameter wrote:
> > Second, arches may use ZONE_DMA in an unknown way. We set CONFIG_ZONE_DMA
> > for all arches that do not set CONFIG_GENERIC_ISA_DMA in order to insure
> > backwards compatibility. The arches may later undefine ZONE_DMA
> > if their arch code has been verified to not depend on ZONE_DMA.
>
> Let's pass this on to linux-arch so that the arch maintainers can give input
> whether they need ZONE_DMA or not. If this just sneaks in unseen I'd bet
> various architectures will just keept it around despite not needing it.
>
sh and sh64 have no use for ZONE_DMA, it's effectively ZONE_DMA =
ZONE_NORMAL anyways, so it can be safely switched off (though
arch/sh/mm/init.c should then be changed to use ZONE_NORMAL if ZONE_DMA
goes away, as we currently place all lowmem in ZONE_DMA, likewise for
sh64). None of our DMA controllers have any particular limitations where
ZONE_DMA would be useful at least.