From: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
To: Timur Tabi <timur-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
Cc: Yoder Stuart-B08248
<B08248-KZfg59tc24xl57MIdRCFDg@public.gmane.org>,
devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org
Subject: Re: question about dma-ranges
Date: Wed, 27 Oct 2010 13:42:27 +1100 [thread overview]
Message-ID: <20101027024227.GD7023@yookeroo> (raw)
In-Reply-To: <AANLkTikTu_p0-Uk7=FuUay4mvCEEU0e9V5eY6bjuK5RQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Tue, Oct 26, 2010 at 08:37:55PM -0500, Timur Tabi wrote:
> On Tue, Oct 26, 2010 at 7:51 PM, Mitch Bradley <wmb-D5eQfiDGL7eakBO8gow8eQ@public.gmane.org> wrote:
> > It's probably unnecessary on modern machines, but old PCs were fairly
> > restrictive about DMA addresses due to short counters. The buses on which
> > such restrictions applied are no longer at the root level, but they were
> > once there...
>
> It's still necessary. The QE, which we ship on several of our current
> parts, can only DMA to/from 32-bit addresses, even on SOCs that
> support 36-bit addressing for everything else.
But the QE is not at the top-level, IIRC, so its restrictions can be
encoded in the dma-ranges on its own bus. We're talking specifically
about the special case of dma-ranges in the root node, not the utility
of dma-ranges in general which is clear.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
next prev parent reply other threads:[~2010-10-27 2:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-27 0:48 question about dma-ranges Yoder Stuart-B08248
[not found] ` <9696D7A991D0824DBA8DFAC74A9C5FA306911C5F-ofAVchDyotYzzZk0BCvKg5jmvxFtTJ+o0e7PPNI6Mm0@public.gmane.org>
2010-10-27 0:51 ` Mitch Bradley
[not found] ` <4CC77784.2070701-D5eQfiDGL7eakBO8gow8eQ@public.gmane.org>
2010-10-27 1:37 ` Timur Tabi
[not found] ` <AANLkTikTu_p0-Uk7=FuUay4mvCEEU0e9V5eY6bjuK5RQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-10-27 2:42 ` David Gibson [this message]
2010-10-27 19:46 ` Scott Wood
[not found] ` <20101027144602.2c5ef098-N/eSCTBpGwP7j4BuCOFQISmX4OfbXNuMKnGXBo5VDl8@public.gmane.org>
2010-10-27 19:47 ` Timur Tabi
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