RE: [Linux-ia64] RE: DMA memory limitation?

["White, Charles" <Charles.White@COMPAQ.com>]

Sorry, just to clarify...  
My device has the limitation that the command buffers I send must be in 32
bit space, but the IO can be in 64 bit.  But there is only ONE dma_mask for
the device.  The way I figured out how to do 64 bit DMA (from reading the
information in the DMA-mapping.txt) was to set my DMA mask of the pci_dev
for my device to allow 64 bit DMA, but when I allocated my command buffers(
with pci_alloc_consistent)  send a pci_dev of NULL.  So I would get the
default of memory that was 24bit addressable.  

This Seg faulted in earlier versions of the IA64 port, but works great in
the latest versions.  But now I have been asked if I can get this to work
with the kernels that are released IA64 CDs.  

So, I was wondering if there was already a patch that would fix this one
problem with the some of the older trees.  

		-----Original Message-----
		From:	Matt_Domsch@Dell.com [mailto:Matt_Domsch@Dell.com]
		Sent:	Monday, July 09, 2001 9:47 AM
		To:	White, Charles
		Cc:	linux-ia64@linuxia64.org
		Subject:	RE: [Linux-ia64] RE: DMA memory limitation?

		> Is there a patch that fixes the pci_alloc_consistent for 
		> older versions of
		> the IA-64 kernels?  To do 64bit DMA in my driver I need to
pass
		> pci_alloc_consistent pci_dev pointer of NULL.  

		You're not going to find such a thing, and it wouldn't make
sense even if
		you did.  See Jeff Garzik's note again:

		>> The important thing is that pci_alloc_consistent and the
other PCI DMA
		>> functions work as advertised on IA64.  If you pass NULL
to
		>> pci_alloc_consistent, IA64 should give you an ISA
DMA-able
		>> address.  If you don't, you get a 32-bit PCI DMA address.

		Never have I seen a using NULL pci_dev pointer give you a
64-bit DMA
		address.  Per Jeff's comment, it should give you an address
with a mask of
		24-bits (within ISA space, i.e. <16MB), but since you can't
add in any ISA
		cards on IA-64, this wouldn't make much sense either.

		At present, the DMA address is entirely dependent upon
pci_dev->dma_mask,
		which by default is a 32-bit mask, and which you can set to
be a 64-bit
		mask.  If you need a 64-bit DMA address, create a new
pci_dev structure, set
		the mask to ~0L and pass that in.  (This may cause other
problems, I can't
		say for certain.)

		Thanks,
		Matt

		--
		Matt Domsch
		Sr. Software Engineer
		Dell Linux Solutions
		www.dell.com/linux
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