firewire: fw-ohci: add option for remote debugging

This way firewire-ohci can be used for remote debugging like ohci1394.
Version with amendment from Fri, 11 Apr 2008 00:08:08 +0200.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Bernhard Kaindl <bk@suse.de>

Documentation/debugging-via-ohci1394.txt

@@ -41,15 +41,19 @@ to a working state and enables physical DMA by default for all remote nodes.
 This can be turned off by ohci1394's module parameter phys_dma=0.
 
 The alternative firewire-ohci driver in drivers/firewire uses filtered physical
-DMA, hence is not yet suitable for remote debugging.
+DMA by default, which is more secure but not suitable for remote debugging.
+Compile the driver with CONFIG_FIREWIRE_OHCI_REMOTE_DMA (Kernel hacking menu:
+Remote debugging over FireWire with firewire-ohci) to get unfiltered physical
+DMA.
 
-Because ohci1394 depends on the PCI enumeration to be completed, an
-initialization routine which runs pretty early (long before console_init()
-which makes the printk buffer appear on the console can be called) was written.
+Because ohci1394 and firewire-ohci depend on the PCI enumeration to be
+completed, an initialization routine which runs pretty early has been
+implemented for x86.  This routine runs long before console_init() can be
+called, i.e. before the printk buffer appears on the console.
 
 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.
+Remote debugging over FireWire early on boot) and pass the parameter
+"ohci1394_dma=early" to the recompiled kernel on boot.
 
 Tools
 -----

drivers/firewire/fw-ohci.c

@@ -1097,6 +1097,11 @@ static void bus_reset_tasklet(unsigned long data)
 		reg_write(ohci, OHCI1394_ConfigROMhdr, ohci->next_header);
 	}
 
+#ifdef CONFIG_FIREWIRE_OHCI_REMOTE_DMA
+	reg_write(ohci, OHCI1394_PhyReqFilterHiSet, ~0);
+	reg_write(ohci, OHCI1394_PhyReqFilterLoSet, ~0);
+#endif
+
 	spin_unlock_irqrestore(&ohci->lock, flags);
 
 	if (free_rom)
@@ -1435,6 +1440,9 @@ static int ohci_cancel_packet(struct fw_card *card, struct fw_packet *packet)
 static int
 ohci_enable_phys_dma(struct fw_card *card, int node_id, int generation)
 {
+#ifdef CONFIG_FIREWIRE_OHCI_REMOTE_DMA
+	return 0;
+#else
 	struct fw_ohci *ohci = fw_ohci(card);
 	unsigned long flags;
 	int n, retval = 0;
@@ -1466,6 +1474,7 @@ ohci_enable_phys_dma(struct fw_card *card, int node_id, int generation)
  out:
 	spin_unlock_irqrestore(&ohci->lock, flags);
 	return retval;
+#endif /* CONFIG_FIREWIRE_OHCI_REMOTE_DMA */
 }
 
 static u64

lib/Kconfig.debug

@@ -593,7 +593,7 @@ config LATENCYTOP
 	  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"
+	bool "Remote debugging over FireWire early on boot"
 	depends on PCI && X86
 	help
 	  If you want to debug problems which hang or crash the kernel early
@@ -621,4 +621,15 @@ config PROVIDE_OHCI1394_DMA_INIT
 
 	  See Documentation/debugging-via-ohci1394.txt for more information.
 
+config FIREWIRE_OHCI_REMOTE_DMA
+	bool "Remote debugging over FireWire with firewire-ohci"
+	depends on FIREWIRE_OHCI
+	help
+	  This option lets you use the FireWire bus for remote debugging
+	  with help of the firewire-ohci driver. It enables unfiltered
+	  remote DMA in firewire-ohci.
+	  See Documentation/debugging-via-ohci1394.txt for more information.
+
+	  If unsure, say N.
+
 source "samples/Kconfig"