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authorStefan Richter <stefanr@s5r6.in-berlin.de>2014-01-18 17:32:20 +0100
committerStefan Richter <stefanr@s5r6.in-berlin.de>2014-01-20 01:11:13 +0100
commitfcd46b34425da52703fe65b7f08850c509dcb0ed (patch)
treea133fd9d86111bbf3de37d882c00e8c3709eea8e /Documentation/debugging-via-ohci1394.txt
parent8bc588e0e585bc9085df75e84d4d5635f45cf360 (diff)
firewire: Enable remote DMA above 4 GB
This makes all of a machine's memory accessible to remote debugging via FireWire, using the physical response unit (i.e. RDMA) of OHCI-1394 link layer controllers. This requires actual support by the controller. The only ones currently known to support it are Agere/LSI FW643. Most if not all other OHCI-1394 controllers do not implement the optional Physical Upper Bound register. With them, RDMA will continue to be limited to the lowermost 4 GB. firewire-ohci's startup message in the kernel log is augmented to tell whether the controller does expose more than 4 GB to RDMA. While OHCI-1394 allows for a maximum Physical Upper Bound of 0xffff'0000'0000 (near 256 TB), this implementation sets it to 0x8000'0000'0000 (128 TB) in order to avoid interference with applications that require interrupt-served asynchronous request reception at respectively low addresses. Note, this change does not switch remote DMA on. It only increases the range of remote access to all memory (instead of just 4 GB) whenever remote DMA was switched on by other means. The latter is achieved by setting firewire-ohci's remote_dma parameter, or if the physical DMA filter is opened through firewire-sbp2. Derived from patch "firewire: Enable physical DMA above 4GB" by Peter Hurley <peter@hurleysoftware.com> from March 27, 2013. Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Diffstat (limited to 'Documentation/debugging-via-ohci1394.txt')
-rw-r--r--Documentation/debugging-via-ohci1394.txt13
1 files changed, 9 insertions, 4 deletions
diff --git a/Documentation/debugging-via-ohci1394.txt b/Documentation/debugging-via-ohci1394.txt
index 73473aa8d861..fa0151a712f9 100644
--- a/Documentation/debugging-via-ohci1394.txt
+++ b/Documentation/debugging-via-ohci1394.txt
@@ -22,10 +22,12 @@ locations such as buffers like the printk buffer or the process table.
Retrieving a full system memory dump is also possible over the FireWire,
using data transfer rates in the order of 10MB/s or more.
-Memory access is currently limited to the low 4G of physical address
-space which can be a problem on IA64 machines where memory is located
-mostly above that limit, but it is rarely a problem on more common
-hardware such as hardware based on x86, x86-64 and PowerPC.
+With most FireWire controllers, memory access is limited to the low 4 GB
+of physical address space. This can be a problem on IA64 machines where
+memory is located mostly above that limit, but it is rarely a problem on
+more common hardware such as x86, x86-64 and PowerPC. However, at least
+Agere/LSI FW643e and FW643e2 controllers are known to support access to
+physical addresses above 4 GB.
Together with a early initialization of the OHCI-1394 controller for debugging,
this facility proved most useful for examining long debugs logs in the printk
@@ -99,6 +101,9 @@ Step-by-step instructions for using firescope with early OHCI initialization:
compliant, they are based on TI PCILynx chips and require drivers for Win-
dows operating systems.
+ The mentioned kernel log message contains ">4 GB phys DMA" in case of
+ OHCI-1394 controllers which support accesses above this limit.
+
2) Establish a working FireWire cable connection:
Any FireWire cable, as long at it provides electrically and mechanically