From: "David S. Miller" <davem@redhat.com>
To: James.Bottomley@HansenPartnership.com
Cc: jes@sunsite.dk, linuxopinion@yahoo.com, linux-kernel@vger.kernel.org
Subject: Re: how to get virtual address from dma address
Date: Wed, 03 Oct 2001 17:24:39 -0700 (PDT) [thread overview]
Message-ID: <20011003.172439.66056954.davem@redhat.com> (raw)
In-Reply-To: <200110032244.f93MiI103485@localhost.localdomain>
In-Reply-To: <200110032244.f93MiI103485@localhost.localdomain>
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Date: Wed, 03 Oct 2001 17:44:18 -0500
(although I can see it may be expensive to walk iommu page tables)
I know of hardware where doing the reverse mapping would not even be
possible, the page tables are in hardware registers and are "write
only". This means you can't even read the PTEs back, you'd have to
keep track of them in software and that is totally unacceptable
overhead when it won't even be used %99 of the time.
The DMA API allows us to support such hardware cleanly and
efficiently, but once we add this feature which "everyone absolutely
needs" we have a problem with the above mentioned piece of hardware.
Franks a lot,
David S. Miller
davem@redhat.com
next prev parent reply other threads:[~2001-10-04 0:24 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.1002355920.6872.linux-kernel2news@redhat.com>
2001-10-03 22:44 ` James Bottomley
2001-10-04 0:24 ` David S. Miller [this message]
2001-10-04 10:11 ` BALBIR SINGH
2001-10-04 11:16 ` David S. Miller
2001-10-04 15:37 ` James Bottomley
2001-10-05 14:06 ` Jes Sorensen
2001-10-06 8:38 ` David S. Miller
2001-10-06 18:19 ` Pete Zaitcev
2001-10-06 18:04 ` Pete Zaitcev
2001-10-06 8:06 ` Paul Mackerras
2001-10-06 12:18 ` Paul Mackerras
2001-10-06 14:45 ` James Bottomley
2001-10-06 16:51 ` Gérard Roudier
2001-10-06 17:23 ` Jes Sorensen
2001-10-07 7:21 ` Gérard Roudier
2001-10-07 16:23 ` James Bottomley
2001-10-07 18:24 ` Gérard Roudier
2001-10-07 23:02 ` James Bottomley
2001-10-08 21:06 ` Gérard Roudier
2001-10-07 2:13 ` Paul Mackerras
2001-10-07 17:40 ` Jes Sorensen
[not found] <Pine.LNX.4.21.0110031525370.14852-100000@pogo.esscom.com>
2001-10-03 21:48 ` Linux Bigot
2001-10-03 22:03 ` Ben Collins
2001-10-05 14:04 ` Jes Sorensen
2001-10-03 21:30 Manfred Spraul
-- strict thread matches above, loose matches on Subject: below --
2001-10-03 16:37 Linux Bigot
2001-10-03 19:32 ` Ben Collins
2001-10-03 21:11 ` Linux Bigot
2001-10-03 21:23 ` Ben Collins
2001-10-03 14:11 Linux Bigot
2001-10-03 15:25 ` Jes Sorensen
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