Re: [Linux-ia64] LINUX IA64 Memory Support

From: Jes Sorensen <>
Date: 2000-02-16 08:03:03
>>>>> "Venkatesh" == Venkatesh Ramamurthy <> writes:

Venkatesh> Hi, Is there any way in which one can allocate memory say
Venkatesh> below 4 GB ( physical address )in drivers.  TIA Venkatesh

This is not IA64 specific actually, so consider it a general answer
rather than an IA64 one.

A regular GFP_KERNEL should give you memory within the PCI DMA'able
area, which with the old PCI system meant within the 4GB
range. GFP_DMA will give you something within the ISA DMA
space. However, in principle none of the above means that the memory
is within the lower 4GB memory range, if the machine in question has
an IOMMU type device, you may be handed memory which is in the middle
of the memory space, but which is mapped to the 4GB the PCI bus in the
machine can see.

With the new PCI allocation system it is even more flexible, here you
may get addresess anywhere and you then tell the PCI subsystem at run
time to map the memory to the space the PCI bus can address. This
means it will be possible to support systems with for instance 200 PCI
busses (if someone feels like building such) etc.

Received on Tue Feb 15 13:03:11 2000

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