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Commit 72548e83 authored by Matt Fleming's avatar Matt Fleming
Browse files

x86/efi: Add EFI framebuffer earlyprintk support 



It's incredibly difficult to diagnose early EFI boot issues without
special hardware because earlyprintk=vga doesn't work on EFI systems.

Add support for writing to the EFI framebuffer, via earlyprintk=efi,
which will actually give users a chance of providing debug output.

Cc: H. Peter Anvin <hpa@zytor.com>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Jones <pjones@redhat.com>
Signed-off-by: default avatarMatt Fleming <matt.fleming@intel.com>
parent c158c3bf

Documentation/kernel-parameters.txt

+5 −3
Original line number Diff line number Diff line
@@ -792,6 +792,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 


	earlyprintk=	[X86,SH,BLACKFIN,ARM]

			earlyprintk=vga

			earlyprintk=efi

			earlyprintk=xen

			earlyprintk=serial[,ttySn[,baudrate]]

			earlyprintk=serial[,0x...[,baudrate]]
@@ -805,7 +806,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			Append ",keep" to not disable it when the real console

			takes over.



			Only vga or serial or usb debug port at a time.

			Only one of vga, efi, serial, or usb debug port can

			be used at a time.



			Currently only ttyS0 and ttyS1 may be specified by

			name.  Other I/O ports may be explicitly specified
@@ -819,8 +821,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			Interaction with the standard serial driver is not

			very good.



			The VGA output is eventually overwritten by the real

			console.

			The VGA and EFI output is eventually overwritten by

			the real console.



			The xen output can only be used by Xen PV guests.

arch/x86/Kconfig.debug

+10 −0
Original line number Diff line number Diff line
@@ -59,6 +59,16 @@ config EARLY_PRINTK_DBGP 
	  with klogd/syslogd or the X server. You should normally N here,

	  unless you want to debug such a crash. You need usb debug device.



config EARLY_PRINTK_EFI

	bool "Early printk via the EFI framebuffer"

	depends on EFI && EARLY_PRINTK

	select FONT_SUPPORT

	---help---

	  Write kernel log output directly into the EFI framebuffer.



	  This is useful for kernel debugging when your machine crashes very

	  early before the console code is initialized.



config X86_PTDUMP

	bool "Export kernel pagetable layout to userspace via debugfs"

	depends on DEBUG_KERNEL

arch/x86/include/asm/efi.h

+2 −0
Original line number Diff line number Diff line
@@ -109,6 +109,8 @@ static inline bool efi_is_native(void) 
	return IS_ENABLED(CONFIG_X86_64) == efi_enabled(EFI_64BIT);

}



extern struct console early_efi_console;



#else

/*

 * IF EFI is not configured, have the EFI calls return -ENOSYS.

arch/x86/kernel/early_printk.c

+7 −0
Original line number Diff line number Diff line
@@ -17,6 +17,8 @@ 
#include <asm/mrst.h>

#include <asm/pgtable.h>

#include <linux/usb/ehci_def.h>

#include <linux/efi.h>

#include <asm/efi.h>



/* Simple VGA output */

#define VGABASE		(__ISA_IO_base + 0xb8000)
@@ -234,6 +236,11 @@ static int __init setup_early_printk(char *buf) 
			early_console_register(&early_hsu_console, keep);

		}

#endif

#ifdef CONFIG_EARLY_PRINTK_EFI

		if (!strncmp(buf, "efi", 3))

			early_console_register(&early_efi_console, keep);

#endif



		buf++;

	}

	return 0;

arch/x86/platform/efi/Makefile

+1 −0
Original line number Diff line number Diff line 
obj-$(CONFIG_EFI) 		+= efi.o efi_$(BITS).o efi_stub_$(BITS).o

obj-$(CONFIG_ACPI_BGRT) += efi-bgrt.o

obj-$(CONFIG_EARLY_PRINTK_EFI)	+= early_printk.o