[PATCH 01/10] ARM: change ARM_DMA_ZONE_SIZE into a variable

[Nicolas Pitre]

On Thu, 7 Jul 2011, Russell King - ARM Linux wrote:

> On Tue, Jul 05, 2011 at 11:12:16PM -0400, Nicolas Pitre wrote:
> > On Wed, 6 Jul 2011, Barry Song wrote:
> > 
> > > 2011/7/6 Nicolas Pitre <nicolas.pitre at linaro.org>:
> > > > Having this value defined at compile time prevents multiple machines with
> > > > conflicting definitions to coexist.  Move it to a variable in preparation
> > > > for having a per machine value selected at run time.  This is relevant
> > > > only when CONFIG_ZONE_DMA is selected.
> > > >
> > > > Signed-off-by: Nicolas Pitre <nicolas.pitre at linaro.org>
> > > 
> > > that is definitely good. i am not sure whether it will be better if
> > > dma zone becomes a property in memory node of DT.
> > 
> > Certainly.  But one thing at a time.  This is the first step. Then, 
> > those machines that are converted to DT could more easily provide the 
> > information via this mechanism if they so desire.
> 
> Actually, putting that information into DT is probably not right -
> you're describing something which is specific to Linux, not something
> which is due to hardware.
> 
> What I mean is that the DMA zone is a Linux specific thing.  Another OS
> could have a different way of dealing with the DMA restrictions (it
> may be possible to allocate memory within a certain set of bounds.)
> 
> What is hardware specific is that the DMA devices can only address a
> limited range of memory.  IMHO it's that which should be described in
> DT, not that we'll have a DMA zone of X bytes in size.

I think that we all agree on the principle.  I certainly never intended 
to suggest that the DMA zone size be stored as is in the device tree.


Nicolas