10 files changed, 526 insertions, 1 deletions

diff --git a/Documentation/debugging-via-ohci1394.txt b/Documentation/debugging-via-ohci1394.txt
new file mode 100644
index 000000000000..de4804e8b396
--- /dev/null
+++ b/Documentation/debugging-via-ohci1394.txt
@@ -0,0 +1,179 @@
+
+  Using physical DMA provided by OHCI-1394 FireWire controllers for debugging
+  ---------------------------------------------------------------------------
+
+Introduction
+------------
+
+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.
+
+With that, it is possible to debug issues by reading interesting memory
+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.
+
+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
+buffer on to debug early boot problems in areas like ACPI where the system
+fails to boot and other means for debugging (serial port) are either not
+available (notebooks) or too slow for extensive debug information (like ACPI).
+
+Drivers
+-------
+
+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.
+
+Because these drivers depend on the PCI enumeration to be completed, an
+initialization routine which can runs pretty early (long before console_init(),
+which makes the printk buffer appear on the console can be called) was written.
+
+To activate it, enable CONFIG_PROVIDE_OHCI1394_DMA_INIT (Kernel hacking menu:
+Provide code for enabling DMA over FireWire early on boot) and pass the
+parameter "ohci1394_dma=early" to the recompiled kernel on boot.
+
+Tools
+-----
+
+firescope - Originally developed by Benjamin Herrenschmidt, Andi Kleen ported
+it from PowerPC to x86 and x86_64 and added functionality, firescope can now
+be used to view the printk buffer of a remote machine, even with live update.
+
+Bernhard Kaindl enhanced firescope to support accessing 64-bit machines
+from 32-bit firescope and vice versa:
+- ftp://ftp.suse.de/private/bk/firewire/tools/firescope-0.2.2.tar.bz2
+
+and he implemented fast system dump (alpha version - read README.txt):
+- ftp://ftp.suse.de/private/bk/firewire/tools/firedump-0.1.tar.bz2
+
+There is also a gdb proxy for firewire which allows to use gdb to access
+data which can be referenced from symbols found by gdb in vmlinux:
+- ftp://ftp.suse.de/private/bk/firewire/tools/fireproxy-0.33.tar.bz2
+
+The latest version of this gdb proxy (fireproxy-0.34) can communicate (not
+yet stable) with kgdb over an memory-based communication module (kgdbom).
+
+Getting Started
+---------------
+
+The OHCI-1394 specification regulates that the OHCI-1394 controller must
+disable all physical DMA on each bus reset.
+
+This means that if you want to debug an issue in a system state where
+interrupts are disabled and where no polling of the OHCI-1394 controller
+for bus resets takes place, you have to establish any FireWire cable
+connections and fully initialize all FireWire hardware __before__ the
+system enters such state.
+
+Step-by-step instructions for using firescope with early OHCI initialization:
+
+1) Verify that your hardware is supported:
+
+   Load the ohci1394 or the fw-ohci module and check your kernel logs.
+   You should see a line similar to
+
+   ohci1394: fw-host0: OHCI-1394 1.1 (PCI): IRQ=[18]  MMIO=[fe9ff800-fe9fffff]
+   ... Max Packet=[2048]  IR/IT contexts=[4/8]
+
+   when loading the driver. If you have no supported controller, many PCI,
+   CardBus and even some Express cards which are fully compliant to OHCI-1394
+   specification are available. If it requires no driver for Windows operating
+   systems, it most likely is. Only specialized shops have cards which are not
+   compliant, they are based on TI PCILynx chips and require drivers for Win-
+   dows operating systems.
+
+2) Establish a working FireWire cable connection:
+
+   Any FireWire cable, as long at it provides electrically and mechanically
+   stable connection and has matching connectors (there are small 4-pin and
+   large 6-pin FireWire ports) will do.
+
+   If an driver is running on both machines you should see a line like
+
+   ieee1394: Node added: ID:BUS[0-01:1023]  GUID[0090270001b84bba]
+
+   on both machines in the kernel log when the cable is plugged in
+   and connects the two machines.
+
+3) Test physical DMA using firescope:
+
+   On the debug host,
+        - load the raw1394 module,
+        - make sure that /dev/raw1394 is accessible,
+   then start firescope:
+
+        $ firescope
+        Port 0 (ohci1394) opened, 2 nodes detected
+
+        FireScope
+        ---------
+        Target : <unspecified>
+        Gen    : 1
+        [Ctrl-T] choose target
+        [Ctrl-H] this menu
+        [Ctrl-Q] quit
+
+    ------> Press Ctrl-T now, the output should be similar to:
+
+        2 nodes available, local node is: 0
+         0: ffc0, uuid: 00000000 00000000 [LOCAL]
+         1: ffc1, uuid: 00279000 ba4bb801
+
+   Besides the [LOCAL] node, it must show another node without error message.
+
+4) Prepare for debugging with early OHCI-1394 initialization:
+
+   4.1) Kernel compilation and installation on debug target
+
+   Compile the kernel to be debugged with CONFIG_PROVIDE_OHCI1394_DMA_INIT
+   (Kernel hacking: Provide code for enabling DMA over FireWire early on boot)
+   enabled and install it on the machine to be debugged (debug target).
+
+   4.2) Transfer the System.map of the debugged kernel to the debug host
+
+   Copy the System.map of the kernel be debugged to the debug host (the host
+   which is connected to the debugged machine over the FireWire cable).
+
+5) Retrieving the printk buffer contents:
+
+   With the FireWire cable connected, the OHCI-1394 driver on the debugging
+   host loaded, reboot the debugged machine, booting the kernel which has
+   CONFIG_PROVIDE_OHCI1394_DMA_INIT enabled, with the option ohci1394_dma=early.
+
+   Then, on the debugging host, run firescope, for example by using -A:
+
+        firescope -A System.map-of-debug-target-kernel
+
+   Note: -A automatically attaches to the first non-local node. It only works
+   reliably if only connected two machines are connected using FireWire.
+
+   After having attached to the debug target, press Ctrl-D to view the
+   complete printk buffer or Ctrl-U to enter auto update mode and get an
+   updated live view of recent kernel messages logged on the debug target.
+
+   Call "firescope -h" to get more information on firescope's options.
+
+Notes
+-----
+Documentation and specifications: ftp://ftp.suse.de/private/bk/firewire/docs
+
+FireWire is a trademark of Apple Inc. - for more information please refer to:
+http://en.wikipedia.org/wiki/FireWire
diff --git a/arch/x86/kernel/setup_32.c b/arch/x86/kernel/setup_32.c
index 9c0ef4945a58..62adc5f20be5 100644
--- a/arch/x86/kernel/setup_32.c
+++ b/arch/x86/kernel/setup_32.c
@@ -45,6 +45,7 @@
 #include <linux/dmi.h>
 #include <linux/pfn.h>
 #include <linux/pci.h>
+#include <linux/init_ohci1394_dma.h>
 
 #include <video/edid.h>
 
@@ -787,6 +788,16 @@ void __init setup_arch(char **cmdline_p)
         smp_alloc_memory(); /* AP processor realmode stacks in low memory*/
 #endif
         paging_init();
+
+        /*
+         * NOTE: On x86-32, only from this point on, fixmaps are ready for use.
+         */
+
+#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
+        if (init_ohci1394_dma_early)
+                init_ohci1394_dma_on_all_controllers();
+#endif
+
         remapped_pgdat_init();
         sparse_init();
         zone_sizes_init();
diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
index 697533e86822..77fb87bf6e5a 100644
--- a/arch/x86/kernel/setup_64.c
+++ b/arch/x86/kernel/setup_64.c
@@ -41,6 +41,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/ctype.h>
 #include <linux/uaccess.h>
+#include <linux/init_ohci1394_dma.h>
 
 #include <asm/mtrr.h>
 #include <asm/uaccess.h>
@@ -253,6 +254,11 @@ void __attribute__((weak)) __init memory_setup(void)
        machine_specific_memory_setup();
 }
 
+/*
+ * setup_arch - architecture-specific boot-time initializations
+ *
+ * Note: On x86_64, fixmaps are ready for use even before this is called.
+ */
 void __init setup_arch(char **cmdline_p)
 {
         unsigned i;
@@ -302,6 +308,11 @@ void __init setup_arch(char **cmdline_p)
 
         parse_early_param();
 
+#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
+        if (init_ohci1394_dma_early)
+                init_ohci1394_dma_on_all_controllers();
+#endif
+
         finish_e820_parsing();
 
         early_gart_iommu_check();
diff --git a/drivers/Makefile b/drivers/Makefile
index 8cb37e3557d4..d92d4d82d001 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -38,7 +38,7 @@ obj-$(CONFIG_SCSI)		+= scsi/
 obj-$(CONFIG_ATA)               += ata/
 obj-$(CONFIG_FUSION)            += message/
 obj-$(CONFIG_FIREWIRE)          += firewire/
-obj-$(CONFIG_IEEE1394)          += ieee1394/
+obj-y                           += ieee1394/
 obj-$(CONFIG_UIO)               += uio/
 obj-y                           += cdrom/
 obj-y                           += auxdisplay/
diff --git a/drivers/ieee1394/Makefile b/drivers/ieee1394/Makefile
index 489c133664d5..1f8153b57503 100644
--- a/drivers/ieee1394/Makefile
+++ b/drivers/ieee1394/Makefile
@@ -15,3 +15,4 @@ obj-$(CONFIG_IEEE1394_SBP2) += sbp2.o
 obj-$(CONFIG_IEEE1394_DV1394) += dv1394.o
 obj-$(CONFIG_IEEE1394_ETH1394) += eth1394.o
 
+obj-$(CONFIG_PROVIDE_OHCI1394_DMA_INIT) += init_ohci1394_dma.o
diff --git a/drivers/ieee1394/init_ohci1394_dma.c b/drivers/ieee1394/init_ohci1394_dma.c
new file mode 100644
index 000000000000..ddaab6eb8ace
--- /dev/null
+++ b/drivers/ieee1394/init_ohci1394_dma.c
@@ -0,0 +1,285 @@
+/*
+ * init_ohci1394_dma.c - Initializes physical DMA on all OHCI 1394 controllers
+ *
+ * Copyright (C) 2006-2007      Bernhard Kaindl <bk@suse.de>
+ *
+ * Derived from drivers/ieee1394/ohci1394.c and arch/x86/kernel/early-quirks.c
+ * this file has functions to:
+ * - scan the PCI very early on boot for all OHCI 1394-compliant controllers
+ * - reset and initialize them and make them join the IEEE1394 bus and
+ * - enable physical DMA on them to allow remote debugging
+ *
+ * All code and data is marked as __init and __initdata, respective as
+ * during boot, all OHCI1394 controllers may be claimed by the firewire
+ * stack and at this point, this code should not touch them anymore.
+ *
+ * To use physical DMA after the initialization of the firewire stack,
+ * be sure that the stack enables it and (re-)attach after the bus reset
+ * which may be caused by the firewire stack initialization.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#include <linux/interrupt.h>    /* for ohci1394.h */
+#include <linux/delay.h>
+#include <linux/pci.h>          /* for PCI defines */
+#include <linux/init_ohci1394_dma.h>
+#include <asm/pci-direct.h>     /* for direct PCI config space access */
+#include <asm/fixmap.h>
+
+#include "ieee1394_types.h"
+#include "ohci1394.h"
+
+int __initdata init_ohci1394_dma_early;
+
+/* Reads a PHY register of an OHCI-1394 controller */
+static inline u8 __init get_phy_reg(struct ti_ohci *ohci, u8 addr)
+{
+        int i;
+        quadlet_t r;
+
+        reg_write(ohci, OHCI1394_PhyControl, (addr << 8) | 0x00008000);
+
+        for (i = 0; i < OHCI_LOOP_COUNT; i++) {
+                if (reg_read(ohci, OHCI1394_PhyControl) & 0x80000000)
+                        break;
+                mdelay(1);
+        }
+        r = reg_read(ohci, OHCI1394_PhyControl);
+
+        return (r & 0x00ff0000) >> 16;
+}
+
+/* Writes to a PHY register of an OHCI-1394 controller */
+static inline void __init set_phy_reg(struct ti_ohci *ohci, u8 addr, u8 data)
+{
+        int i;
+
+        reg_write(ohci, OHCI1394_PhyControl, (addr << 8) | data | 0x00004000);
+
+        for (i = 0; i < OHCI_LOOP_COUNT; i++) {
+                u32 r = reg_read(ohci, OHCI1394_PhyControl);
+                if (!(r & 0x00004000))
+                        break;
+                mdelay(1);
+        }
+}
+
+/* Resets an OHCI-1394 controller (for sane state before initialization) */
+static inline void __init init_ohci1394_soft_reset(struct ti_ohci *ohci) {
+        int i;
+
+        reg_write(ohci, OHCI1394_HCControlSet, OHCI1394_HCControl_softReset);
+
+        for (i = 0; i < OHCI_LOOP_COUNT; i++) {
+                if (!(reg_read(ohci, OHCI1394_HCControlSet)
+                                   & OHCI1394_HCControl_softReset))
+                        break;
+                mdelay(1);
+        }
+}
+
+/* Basic OHCI-1394 register and port inititalization */
+static inline void __init init_ohci1394_initialize(struct ti_ohci *ohci)
+{
+        quadlet_t bus_options;
+        int num_ports, i;
+
+        /* Put some defaults to these undefined bus options */
+        bus_options = reg_read(ohci, OHCI1394_BusOptions);
+        bus_options |=  0x60000000; /* Enable CMC and ISC */
+        bus_options &= ~0x00ff0000; /* XXX: Set cyc_clk_acc to zero for now */
+        bus_options &= ~0x18000000; /* Disable PMC and BMC */
+        reg_write(ohci, OHCI1394_BusOptions, bus_options);
+
+        /* Set the bus number */
+        reg_write(ohci, OHCI1394_NodeID, 0x0000ffc0);
+
+        /* Enable posted writes */
+        reg_write(ohci, OHCI1394_HCControlSet,
+                        OHCI1394_HCControl_postedWriteEnable);
+
+        /* Clear link control register */
+        reg_write(ohci, OHCI1394_LinkControlClear, 0xffffffff);
+
+        /* enable phys */
+        reg_write(ohci, OHCI1394_LinkControlSet,
+                        OHCI1394_LinkControl_RcvPhyPkt);
+
+        /* Don't accept phy packets into AR request context */
+        reg_write(ohci, OHCI1394_LinkControlClear, 0x00000400);
+
+        /* Clear the Isochonouys interrupt masks */
+        reg_write(ohci, OHCI1394_IsoRecvIntMaskClear, 0xffffffff);
+        reg_write(ohci, OHCI1394_IsoRecvIntEventClear, 0xffffffff);
+        reg_write(ohci, OHCI1394_IsoXmitIntMaskClear, 0xffffffff);
+        reg_write(ohci, OHCI1394_IsoXmitIntEventClear, 0xffffffff);
+
+        /* Accept asyncronous transfer requests from all nodes for now */
+        reg_write(ohci,OHCI1394_AsReqFilterHiSet, 0x80000000);
+
+        /* Specify asyncronous transfer retries */
+        reg_write(ohci, OHCI1394_ATRetries,
+                  OHCI1394_MAX_AT_REQ_RETRIES |
+                  (OHCI1394_MAX_AT_RESP_RETRIES<<4) |
+                  (OHCI1394_MAX_PHYS_RESP_RETRIES<<8));
+
+        /* We don't want hardware swapping */
+        reg_write(ohci, OHCI1394_HCControlClear, OHCI1394_HCControl_noByteSwap);
+
+        /* Enable link */
+        reg_write(ohci, OHCI1394_HCControlSet, OHCI1394_HCControl_linkEnable);
+
+        /* If anything is connected to a port, make sure it is enabled */
+        num_ports = get_phy_reg(ohci, 2) & 0xf;
+        for (i = 0; i < num_ports; i++) {
+                unsigned int status;
+
+                set_phy_reg(ohci, 7, i);
+                status = get_phy_reg(ohci, 8);
+
+                if (status & 0x20)
+                        set_phy_reg(ohci, 8, status & ~1);
+        }
+}
+
+/**
+ * init_ohci1394_wait_for_busresets - wait until bus resets are completed
+ *
+ * OHCI1394 initialization itself and any device going on- or offline
+ * and any cable issue cause a IEEE1394 bus reset. The OHCI1394 spec
+ * specifies that physical DMA is disabled on each bus reset and it
+ * has to be enabled after each bus reset when needed. We resort
+ * to polling here because on early boot, we have no interrupts.
+ */
+static inline void __init init_ohci1394_wait_for_busresets(struct ti_ohci *ohci)
+{
+        int i, events;
+
+        for (i=0; i < 9; i++) {
+                mdelay(200);
+                events = reg_read(ohci, OHCI1394_IntEventSet);
+                if (events & OHCI1394_busReset)
+                        reg_write(ohci, OHCI1394_IntEventClear,
+                                        OHCI1394_busReset);
+        }
+}
+
+/**
+ * init_ohci1394_enable_physical_dma - Enable physical DMA for remote debugging
+ * This enables remote DMA access over IEEE1394 from every host for the low
+ * 4GB of address space. DMA accesses above 4GB are not available currently.
+ */
+static inline void __init init_ohci1394_enable_physical_dma(struct ti_ohci *hci)
+{
+        reg_write(hci, OHCI1394_PhyReqFilterHiSet, 0xffffffff);
+        reg_write(hci, OHCI1394_PhyReqFilterLoSet, 0xffffffff);
+        reg_write(hci, OHCI1394_PhyUpperBound, 0xffff0000);
+}
+
+/**
+ * init_ohci1394_reset_and_init_dma - init controller and enable DMA
+ * This initializes the given controller and enables physical DMA engine in it.
+ */
+static inline void __init init_ohci1394_reset_and_init_dma(struct ti_ohci *ohci)
+{
+        /* Start off with a soft reset, clears everything to a sane state. */
+        init_ohci1394_soft_reset(ohci);
+
+        /* Accessing some registers without LPS enabled may cause lock up */
+        reg_write(ohci, OHCI1394_HCControlSet, OHCI1394_HCControl_LPS);
+
+        /* Disable and clear interrupts */
+        reg_write(ohci, OHCI1394_IntEventClear, 0xffffffff);
+        reg_write(ohci, OHCI1394_IntMaskClear, 0xffffffff);
+
+        mdelay(50); /* Wait 50msec to make sure we have full link enabled */
+
+        init_ohci1394_initialize(ohci);
+        /*
+         * The initialization causes at least one IEEE1394 bus reset. Enabling
+         * physical DMA only works *after* *all* bus resets have calmed down:
+         */
+        init_ohci1394_wait_for_busresets(ohci);
+
+        /* We had to wait and do this now if we want to debug early problems */
+        init_ohci1394_enable_physical_dma(ohci);
+}
+
+/**
+ * init_ohci1394_controller - Map the registers of the controller and init DMA
+ * This maps the registers of the specified controller and initializes it
+ */
+static inline void __init init_ohci1394_controller(int num, int slot, int func)
+{
+        unsigned long ohci_base;
+        struct ti_ohci ohci;
+
+        printk(KERN_INFO "init_ohci1394_dma: initializing OHCI-1394"
+                         " at %02x:%02x.%x\n", num, slot, func);
+
+        ohci_base = read_pci_config(num, slot, func, PCI_BASE_ADDRESS_0+(0<<2))
+                                                   & PCI_BASE_ADDRESS_MEM_MASK;
+
+        set_fixmap_nocache(FIX_OHCI1394_BASE, ohci_base);
+
+        ohci.registers = (void *)fix_to_virt(FIX_OHCI1394_BASE);
+
+        init_ohci1394_reset_and_init_dma(&ohci);
+}
+
+/**
+ * debug_init_ohci1394_dma - scan for OHCI1394 controllers and init DMA on them
+ * Scans the whole PCI space for OHCI1394 controllers and inits DMA on them
+ */
+void __init init_ohci1394_dma_on_all_controllers(void)
+{
+        int num, slot, func;
+
+        if (!early_pci_allowed())
+                return;
+
+        /* Poor man's PCI discovery, the only thing we can do at early boot */
+        for (num = 0; num < 32; num++) {
+                for (slot = 0; slot < 32; slot++) {
+                        for (func = 0; func < 8; func++) {
+                                u32 class = read_pci_config(num,slot,func,
+                                                        PCI_CLASS_REVISION);
+                                if ((class == 0xffffffff))
+                                        continue; /* No device at this func */
+
+                                if (class>>8 != PCI_CLASS_SERIAL_FIREWIRE_OHCI)
+                                        continue; /* Not an OHCI-1394 device */
+
+                                init_ohci1394_controller(num, slot, func);
+                                break; /* Assume one controller per device */
+                        }
+                }
+        }
+        printk(KERN_INFO "init_ohci1394_dma: finished initializing OHCI DMA\n");
+}
+
+/**
+ * setup_init_ohci1394_early - enables early OHCI1394 DMA initialization
+ */
+static int __init setup_ohci1394_dma(char *opt)
+{
+        if (!strcmp(opt, "early"))
+                init_ohci1394_dma_early = 1;
+        return 0;
+}
+
+/* passing ohci1394_dma=early on boot causes early OHCI1394 DMA initialization */
+early_param("ohci1394_dma", setup_ohci1394_dma);
diff --git a/include/asm-x86/fixmap_32.h b/include/asm-x86/fixmap_32.h
index fde140fd6d95..a7404d50686b 100644
--- a/include/asm-x86/fixmap_32.h
+++ b/include/asm-x86/fixmap_32.h
@@ -104,6 +104,9 @@ enum fixed_addresses {
                         (__end_of_permanent_fixed_addresses & 511),
         FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_NESTING - 1,
         FIX_WP_TEST,
+#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
+        FIX_OHCI1394_BASE,
+#endif
         __end_of_fixed_addresses
 };
 
diff --git a/include/asm-x86/fixmap_64.h b/include/asm-x86/fixmap_64.h
index 8f44782e5fe5..70ddb21e6458 100644
--- a/include/asm-x86/fixmap_64.h
+++ b/include/asm-x86/fixmap_64.h
@@ -44,6 +44,9 @@ enum fixed_addresses {
         FIX_IO_APIC_BASE_END = FIX_IO_APIC_BASE_0 + MAX_IO_APICS-1,
         FIX_EFI_IO_MAP_LAST_PAGE,
         FIX_EFI_IO_MAP_FIRST_PAGE = FIX_EFI_IO_MAP_LAST_PAGE+MAX_EFI_IO_PAGES-1,
+#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
+        FIX_OHCI1394_BASE,
+#endif
         __end_of_fixed_addresses
 };
 
diff --git a/include/linux/init_ohci1394_dma.h b/include/linux/init_ohci1394_dma.h
new file mode 100644
index 000000000000..3c03a4bba5e4
--- /dev/null
+++ b/include/linux/init_ohci1394_dma.h
@@ -0,0 +1,4 @@
+#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
+extern int __initdata init_ohci1394_dma_early;
+extern void __init init_ohci1394_dma_on_all_controllers(void);
+#endif
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index aa56e631580d..89f4035b526c 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -586,5 +586,33 @@ config LATENCYTOP
           Enable this option if you want to use the LatencyTOP tool
           to find out which userspace is blocking on what kernel operations.
 
+config PROVIDE_OHCI1394_DMA_INIT
+        bool "Provide code for enabling DMA over FireWire early on boot"
+        depends on PCI && X86
+        help
+          If you want to debug problems which hang or crash the kernel early
+          on boot and the crashing machine has a FireWire port, you can use
+          this feature to remotely access the memory of the crashed machine
+          over FireWire. This employs remote DMA as part of the OHCI1394
+          specification which is now the standard for FireWire controllers.
+
+          With remote DMA, you can monitor the printk buffer remotely using
+          firescope and access all memory below 4GB using fireproxy from gdb.
+          Even controlling a kernel debugger is possible using remote DMA.
+
+          Usage:
+
+          If ohci1394_dma=early is used as boot parameter, it will initialize
+          all OHCI1394 controllers which are found in the PCI config space.
+
+          As all changes to the FireWire bus such as enabling and disabling
+          devices cause a bus reset and thereby disable remote DMA for all
+          devices, be sure to have the cable plugged and FireWire enabled on
+          the debugging host before booting the debug target for debugging.
+
+          This code (~1k) is freed after boot. By then, the firewire stack
+          in charge of the OHCI-1394 controllers should be used instead.
+
+          See Documentation/debugging-via-ohci1394.txt for more information.
 
 source "samples/Kconfig"