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powerpc: Add an in memory udbg console

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This patch adds a new udbg early debug console which utilises
statically defined input and output buffers stored within the kernel
BSS. It is primarily designed to assist with bring up of new hardware
which may not have a working console but which has a method of
reading/writing kernel memory.

This version incorporates comments made by Ben H (thanks!).

Changes from v1:
	- Add memory barriers.
	- Ensure updating of read/write positions is atomic.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Alistair Popple
2013-04-29 18:07:47 +00:00
committed by Benjamin Herrenschmidt
parent 5737789c83
commit 30650239ad
5 changed files with 134 additions and 0 deletions
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23
arch/powerpc/Kconfig.debug
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@@ -262,8 +262,31 @@ config PPC_EARLY_DEBUG_OPAL_HVSI
Select this to enable early debugging for the PowerNV platform
using an "hvsi" console
config PPC_EARLY_DEBUG_MEMCONS
bool "In memory console"
help
Select this to enable early debugging using an in memory console.
This console provides input and output buffers stored within the
kernel BSS and should be safe to select on any system. A debugger
can then be used to read kernel output or send input to the console.
endchoice
config PPC_MEMCONS_OUTPUT_SIZE
int "In memory console output buffer size"
depends on PPC_EARLY_DEBUG_MEMCONS
default 4096
help
Selects the size of the output buffer (in bytes) of the in memory
console.
config PPC_MEMCONS_INPUT_SIZE
int "In memory console input buffer size"
depends on PPC_EARLY_DEBUG_MEMCONS
default 128
help
Selects the size of the input buffer (in bytes) of the in memory
console.
config PPC_EARLY_DEBUG_OPAL
def_bool y
depends on PPC_EARLY_DEBUG_OPAL_RAW || PPC_EARLY_DEBUG_OPAL_HVSI