From: Roland Dreier <rdreier@cisco.com>
To: "Caitlin Bestler" <caitlinb@broadcom.com>
Cc: "Grant Grundler" <iod00d@hp.com>,
openib-general@openib.org, linux-kernel@vger.kernel.org,
"Segher Boessenkool" <segher@kernel.crashing.org>
Subject: Re: [openib-general] Re: [PATCH 21 of 53] ipath - use phys_to_virt instead of bus_to_virt
Date: Mon, 15 May 2006 16:50:11 -0700 [thread overview]
Message-ID: <adabqtyrgp8.fsf@cisco.com> (raw)
In-Reply-To: <54AD0F12E08D1541B826BE97C98F99F149F34B@NT-SJCA-0751.brcm.ad.broadcom.com> (Caitlin Bestler's message of "Mon, 15 May 2006 16:40:35 -0700")
Caitlin> True, but how does that constrain the local interfaces by
Caitlin> which the driver is informed of the set of pages that
Caitlin> back a given memory region? The driver must still
Caitlin> ultimately provide dma accessible addresses to the
Caitlin> device. RDMA just changes the timing of the steps, albeit
Caitlin> radically, but not what the steps are.
It's only a problem for "reserved L_Key" types of things, where the
device is supposed to just use the address given in a work request
without translating it. No translation means that work requests have
to contain "bus addresses" -- addresses that are what the device would
put on the bus to access memory. But if a device needs to simulate
DMA in software, then it really needs a kernel virtual address, not a
bus address. But it's pretty ugly to have to put that knowledge in
every consumer.
- R.
next prev parent reply other threads:[~2006-05-15 23:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-15 23:40 [openib-general] Re: [PATCH 21 of 53] ipath - use phys_to_virt instead of bus_to_virt Caitlin Bestler
2006-05-15 23:50 ` Roland Dreier [this message]
-- strict thread matches above, loose matches on Subject: below --
2006-05-12 23:43 Bryan O'Sullivan
2006-05-15 15:50 ` Roland Dreier
2006-05-15 21:21 ` Bryan O'Sullivan
2006-05-15 21:28 ` Roland Dreier
2006-05-15 23:13 ` [openib-general] " Grant Grundler
2006-05-15 23:16 ` Roland Dreier
2006-05-15 23:30 ` Grant Grundler
2006-05-15 23:34 ` Roland Dreier
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