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x86/efi: Add EFI framebuffer earlyprintk support

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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: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Jones <pjones@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
This commit is contained in:
Matt Fleming
2013-10-04 09:36:56 +01:00
parent c158c3bf59
commit 72548e836b
6 changed files with 216 additions and 3 deletions
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8
Documentation/kernel-parameters.txt
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@@ -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.