[alsa-devel] [LKML] Re: USB transfer_buffer allocations on 64bit systems

[Alan Stern]

On Fri, 9 Apr 2010, Konrad Rzeszutek Wilk wrote:

> On Fri, Apr 09, 2010 at 03:34:06PM -0400, Alan Stern wrote:
> > On Fri, 9 Apr 2010, Pedro Ribeiro wrote:
> > 
> > > > The DMA pointers do indeed look sane. I wanted to take a deeper look at
> > > > this and set up a 64bit system today. However, I fail to see the problem
> > > > here. Pedro, how much RAM does your machine have installed?
> > 
> > > It has 4 GB.
> > 
> > That means DMA mapping cannot be the cause of the problem.  :-(
> 
> That isn't entirely true. The BIOS usually allocates a 256 MB ACPI/PCI hole
> that is under the 4GB.
> 
> So end up with 3.7 GB, then the 256MB hole, and then right above the 4GB
> you the the remaining memory: 4.3GB.

How can Pedro find out what physical addresses are in use on his 
system?

Alan Stern