linux-kernel - [PATCH] firewire: Enable remote DMA above 4 GB

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Date:	Sat, 18 Jan 2014 16:33:15 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	linux1394-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>,
	Clemens Ladisch <clemens@...isch.de>
Subject: [PATCH] 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.

Derived from patch "firewire: Enable physical DMA above 4GB" by
Peter Hurley <peter@...leysoftware.com> from March 27, 2013.

Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
---
 drivers/firewire/core-transaction.c |    6 +++---
 drivers/firewire/core.h             |    3 +++
 drivers/firewire/ohci.c             |    8 +++++---
 3 files changed, 11 insertions(+), 6 deletions(-)

--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -523,11 +523,11 @@ static DEFINE_SPINLOCK(address_handler_l
 static LIST_HEAD(address_handler_list);
 
 const struct fw_address_region fw_high_memory_region =
-	{ .start = 0x000100000000ULL, .end = 0xffffe0000000ULL,  };
+	{ .start = FW_MAX_PHYSICAL_RANGE, .end = 0xffffe0000000ULL, };
 EXPORT_SYMBOL(fw_high_memory_region);
 
 static const struct fw_address_region low_memory_region =
-	{ .start = 0x000000000000ULL, .end = 0x000100000000ULL,  };
+	{ .start = 0x000000000000ULL, .end = FW_MAX_PHYSICAL_RANGE, };
 
 #if 0
 const struct fw_address_region fw_private_region =
@@ -1217,7 +1217,7 @@ static void handle_low_memory(struct fw_
 }
 
 static struct fw_address_handler low_memory = {
-	.length			= 0x000100000000ULL,
+	.length			= FW_MAX_PHYSICAL_RANGE,
 	.address_callback	= handle_low_memory,
 };
 
--- a/drivers/firewire/core.h
+++ b/drivers/firewire/core.h
@@ -237,6 +237,9 @@ static inline bool is_next_generation(in
 
 #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);
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -2367,7 +2367,7 @@ static int ohci_enable(struct fw_card *c
 	reg_write(ohci, OHCI1394_FairnessControl, 0);
 	card->priority_budget_implemented = ohci->pri_req_max != 0;
 
-	reg_write(ohci, OHCI1394_PhyUpperBound, 0x00010000);
+	reg_write(ohci, OHCI1394_PhyUpperBound, FW_MAX_PHYSICAL_RANGE >> 16);
 	reg_write(ohci, OHCI1394_IntEventClear, ~0);
 	reg_write(ohci, OHCI1394_IntMaskClear, ~0);
 
@@ -3723,9 +3723,11 @@ static int pci_probe(struct pci_dev *dev
 	version = reg_read(ohci, OHCI1394_Version) & 0x00ff00ff;
 	ohci_notice(ohci,
 		    "added OHCI v%x.%x device as card %d, "
-		    "%d IR + %d IT contexts, quirks 0x%x\n",
+		    "%d IR + %d IT contexts, quirks 0x%x%s\n",
 		    version >> 16, version & 0xff, ohci->card.index,
-		    ohci->n_ir, ohci->n_it, ohci->quirks);
+		    ohci->n_ir, ohci->n_it, ohci->quirks,
+		    reg_read(ohci, OHCI1394_PhyUpperBound) ?
+			", >4 GB phys DMA" : "");
 
 	return 0;
 


-- 
Stefan Richter
-=====-====- ---= =--=-
http://arcgraph.de/sr/
--
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