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>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/firewire/core.h b/drivers/firewire/core.h
index 515a42c..c98764a 100644
--- a/drivers/firewire/core.h
+++ b/drivers/firewire/core.h
@@ -237,6 +237,9 @@ static inline bool is_next_generation(int new_generation, int old_generation)
 
 #define LOCAL_BUS 0xffc0
 
+/* arbitrarily chosen maximum range for physical DMA: 128 TB */
+#define FW_MAX_PHYSICAL_RANGE		(128ULL << 40)
+
 void fw_core_handle_request(struct fw_card *card, struct fw_packet *request);
 void fw_core_handle_response(struct fw_card *card, struct fw_packet *packet);
 int fw_get_response_length(struct fw_request *request);