From: Stefan Richter <firstname.lastname@example.org>
To: Bernhard Kaindl <email@example.com>
Cc: Andi Kleen <firstname.lastname@example.org>, Bernhard Kaindl <email@example.com>,
Thomas Renninger <firstname.lastname@example.org>,
Benjamin Herrenschmidt <email@example.com>
Subject: Re: [PATCH] Early boot debugging via FireWire (ohci1394_dma=early)
Date: Thu, 06 Dec 2007 21:23:41 +0100 [thread overview]
Message-ID: <47585A4D.firstname.lastname@example.org> (raw)
Bernhard Kaindl wrote:
> after summing up the discussion on previous patches, I'm now submitting the
> patch below for formal review and adoption on branches for mainline inclusion.
I will look a bit more into the details later; for now I have just a
quick comment on the documentation.
> --- linux-2.6.24-rc4/Documentation/debugging-via-ohci1394.txt
> +++ linux-2.6.24-rc4/Documentation/debugging-via-ohci1394.txt
> @@ -0,0 +1,179 @@
> + Using physical DMA provided by OHCI-1394 FireWire controllers for debugging
> + ---------------------------------------------------------------------------
There are some really long sentences in it.
Try to use the "." character more often. :-)
> +Basically all FireWire controllers which are in use today are compliant
> +to the OHCI-1394 specification which defines the controller to be a PCI
> +bus master which uses DMA to offload data transfers from the CPU and has
> +a "Physical Response Unit" which executes specific requests by employing
> +PCI-Bus master DMA after applying filters defined by the OHCI-1394 driver.
> +Once properly configured, remote machines can send these requests to
> +ask the OHCI-1394 controller to perform read and write requests on
> +physical system memory and, for read requests, send the result of
> +the physical memory read back to the requester.
In other words, the FireWire controller can be configured to work as a
bus bridge between FireWire bus and local bus (PCI or PCIe).
And yes, there are security implications.
> +The OHCI-1394 drivers in drivers/firewire and drivers/ieee1394 initialize
> +the OHCI-1394 controllers to a working state and can be used to enable
> +physical DMA. By default you only have to load the driver, and physical
> +DMA access will be granted to all remote nodes, but it can be turned off
> +when using the ohci1394 driver.
This is correct for ohci1394, and it's a bug.
firewire-ohci however implements filtered physical DMA. The only user
of that is the firewire-sbp2 driver which grants SBP-2 targets access
through the physical response unit. firewire-ohci has at the moment no
option for either unfiltered physical DMA (as needed by firescope at al,
tracked at http://wiki.linux1394.org/ToDo) nor to completely disable
-=====-=-=== ==-- --==-
next prev parent reply other threads:[~2007-12-06 20:24 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-10 11:42 What will be in the x86-64/x86 2.6.21 merge Andi Kleen
2007-02-10 13:43 ` [discuss] " Muli Ben-Yehuda
2007-02-10 13:52 ` Andi Kleen
2007-02-10 13:56 ` Muli Ben-Yehuda
2007-02-10 14:03 ` Andi Kleen
2007-02-10 13:51 ` remote debugging via FireWire (was What will be in the x86-64/x86 2.6.21 merge) Stefan Richter
2007-02-10 14:02 ` Andi Kleen
2007-02-10 15:14 ` remote debugging via FireWire Stefan Richter
2007-02-10 15:41 ` Andi Kleen
2007-02-10 19:16 ` Stefan Richter
2007-02-11 21:35 ` Benjamin Herrenschmidt
2007-02-12 6:49 ` Andi Kleen
2007-02-12 7:29 ` Benjamin Herrenschmidt
2007-12-04 3:45 ` remote debugging via FireWire * __fast__ firedump! Bernhard Kaindl
2007-12-04 7:39 ` Andi Kleen
2007-12-06 16:02 ` Bernhard Kaindl
2007-12-04 22:15 ` Stefan Richter
2007-12-04 22:34 ` Stefan Richter
2007-12-04 22:40 ` Stefan Richter
2007-12-06 18:36 ` [feedback discussion] Early boot debugging via FireWire (ohci1394_dma=early) Bernhard Kaindl
2007-12-06 19:23 ` Stefan Richter
2007-12-06 19:23 ` [PATCH] " Bernhard Kaindl
2007-12-06 20:23 ` Stefan Richter [this message]
2007-12-17 13:49 ` Ingo Molnar
2007-12-06 16:32 ` remote debugging via FireWire * __fast__ firedump! Bernhard Kaindl
2007-02-12 14:11 ` What will be in the x86-64/x86 2.6.21 merge James Morris
2007-02-12 14:14 ` Andi Kleen
2007-02-12 14:46 ` James Morris
2007-02-14 6:53 ` Rusty Russell
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