linux-kernel - Re: [PATCH] firewire: Enable physical DMA above 4GB

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Date:	Tue, 26 Mar 2013 19:22:55 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Stefan Richter <stefanr@...6.in-berlin.de>,
	linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firewire: Enable physical DMA above 4GB

Peter Hurley wrote:
> On Tue, 2013-03-26 at 17:12 +0100, Clemens Ladisch wrote:
>> Peter Hurley wrote:
>>> Write the PhyUpperBound register with the end-of-memory value. If
>>> end-of-memory is beyond the OHCI limit of 0x0000ffff00000000,
>>> clamp to that value.
>>
>> You will have to lower this limit; there are protcols that assume that
>> addresses like 0xecc000000000 are available for software.
>
> Maybe 0x0000e80000000000 is a better maximum upper bound?

Why the space of 0x04c000000000?  ;-)

There's also 0xc007dedadada (although this address isn't used on the PC
side).  Maybe we should just round down to 0x800000000000 and revisit
the question when there are 256 TB memory machines.  (Directly accessing
the full 256 TB will not be possible in any case.)


Regards,
Clemens
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