Re: [PATCH 2/6] Introduce CONFIG_ZONE_DMA

[Christoph Hellwig <hch@infradead.org>]

On Mon, Sep 11, 2006 at 03:27:39PM -0700, Christoph Lameter wrote:
> Introduce CONFIG_ZONE_DMA
> 
> This patch simply defines CONFIG_ZONE_DMA for all arches. We later do
> special things with CONFIG_ZONE_DMA after the VM and an arch are
> prepared to work without ZONE_DMA.
> 
> CONFIG_ZONE_DMA can be defined in two ways depending on how
> an architecture handles ISA DMA.
> 
> First if CONFIG_GENERIC_ISA_DMA is set by the arch then we know that
> the arch needs ZONE_DMA because ISA DMA devices are supported. We
> can catch this in mm/Kconfig and do not need to modify arch code.
> 
> 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.