[PATCH v8 3/5] x86: add support for earlyprintk via USB3 debug port

[Lu Baolu <baolu.lu@linux.intel.com>]

Add support for earlyprintk by writing debug messages to the
USB3 debug port. Users can use this type of early printk by
specifying the kernel parameter of "earlyprintk=xdbc". This
gives users a chance of providing debugging output.

The hardware for USB3 debug port requires DMA memory blocks.
This requires to delay setting up debugging hardware and
registering boot console until the memblocks are filled.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: x86@kernel.org
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 1 +
 arch/x86/kernel/early_printk.c                  | 5 +++++
 arch/x86/kernel/setup.c                         | 4 ++++
 3 files changed, 10 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2ba45ca..ea1293d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -989,6 +989,7 @@
 			earlyprintk=ttySn[,baudrate]
 			earlyprintk=dbgp[debugController#]
 			earlyprintk=pciserial,bus:device.function[,baudrate]
+			earlyprintk=xdbc[xhciController#]
 
 			earlyprintk is useful when the kernel crashes before
 			the normal console is initialized. It is not enabled by
diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index 8a12199..0f08403 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -17,6 +17,7 @@
 #include <asm/intel-mid.h>
 #include <asm/pgtable.h>
 #include <linux/usb/ehci_def.h>
+#include <linux/usb/xhci-dbgp.h>
 #include <linux/efi.h>
 #include <asm/efi.h>
 #include <asm/pci_x86.h>
@@ -381,6 +382,10 @@ static int __init setup_early_printk(char *buf)
 		if (!strncmp(buf, "efi", 3))
 			early_console_register(&early_efi_console, keep);
 #endif
+#ifdef CONFIG_EARLY_PRINTK_USB_XDBC
+		if (!strncmp(buf, "xdbc", 4))
+			early_xdbc_parse_parameter(buf + 4);
+#endif
 
 		buf++;
 	}
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index e70204e..2600b1d 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -70,6 +70,7 @@
 #include <linux/tboot.h>
 #include <linux/jiffies.h>
 
+#include <linux/usb/xhci-dbgp.h>
 #include <video/edid.h>
 
 #include <asm/mtrr.h>
@@ -1144,6 +1145,9 @@ void __init setup_arch(char **cmdline_p)
 	memblock_set_current_limit(ISA_END_ADDRESS);
 	memblock_x86_fill();
 
+	if (!early_xdbc_setup_hardware())
+		early_xdbc_register_console();
+
 	reserve_bios_regions();
 
 	if (efi_enabled(EFI_MEMMAP)) {
-- 
2.1.4