[Linux-ia64] Re: PCI DAC routines for SN

[Jesse Barnes <jbarnes@sgi.com>]

On Wed, Apr 24, 2002 at 05:08:08PM -0700, David S. Miller wrote:
>    So if performance isn't an obstacle to implementing a new call, and
>    I've shown that there are platforms where 64 bit consistent mappings
>    are better to use than 32 bit mappings when possible, why can't we add
>    it?  Or maybe just a seperate consistent_mask that drivers could set
>    to indicate they support the operation and let the platform take care
>    of it?
>    
> Where is the platform where it is a problem to keep around
> enough of the _4_ __GIGABYTES__ of consistent memory available
> at bootup?
> 
> If you can't keep around enough consistent memory within the
> lower 4GB, you have other problems.
> 
> Devices use, EACH, something like a few kilobytes of consistent
> memory for descriptors.  If you are going to tell me this is
> a big deal, you have to be kidding me.
> 
> Why don't you tell me what the real problem is?

I thought I did.  The issue isn't keeping 4gb around, it's using up
the 32 bit mappings in the bridge for 64 bit capable cards.

Jesse