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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20101027024227.GD7023@yookeroo \
--to=david-xt8fgy+axnrb3ne2bgzf6laj5h9x9tb+@public.gmane.org \
--cc=B08248-KZfg59tc24xl57MIdRCFDg@public.gmane.org \
--cc=devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org \
--cc=timur-KZfg59tc24xl57MIdRCFDg@public.gmane.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.