Re: alpha iommu fixes

Jonathan Lundell (jlundell@pobox.com)
Tue, 22 May 2001 13:48:23 -0700

At 1:28 PM -0700 2001-05-22, Richard Henderson wrote:
>On Tue, May 22, 2001 at 05:00:16PM +0200, Andrea Arcangeli wrote:
>> I'm also wondering if ISA needs the sg to start on a 64k boundary,
>
>Traditionally, ISA could not do DMA across a 64k boundary.
>
>The only ISA card I have (a soundblaster compatible) appears
>to work without caring for this, but I suppose we should pay
>lip service to pedantics.

64KB for 8-bit DMA; 128KB for 16-bit DMA. It's a limitation of the
legacy third-party-DMA controllers, which had only 16-bit address
registers (the high part of the address lives in a non-counting
register). This doesn't apply to bus-master DMA, just the legacy
(8237) stuff. There was also a 24-bit address limitation.

-- 
/Jonathan Lundell.
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