Messages in this thread | | | Date | Thu, 06 Dec 2007 21:23:41 +0100 | From | Stefan Richter <> | Subject | Re: [PATCH] Early boot debugging via FireWire (ohci1394_dma=early) |
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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 > + --------------------------------------------------------------------------- > + > +Introduction > +------------
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. http://bugzilla.kernel.org/show_bug.cgi?id=7794
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 physical DMA. -- Stefan Richter -=====-=-=== ==-- --==- http://arcgraph.de/sr/
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