On 06/25/2013 01:11:00 PM, Leif Lindholm wrote:
This patch provides documentation of the [U]EFI runtime services and
configuration features.
Signed-off-by: Leif Lindholm <leif.lindholm@xxxxxxxxxx>
---
Documentation/arm/00-INDEX | 3 +++
Documentation/arm/uefi.txt | 39
+++++++++++++++++++++++++++++++++++++++
2 files changed, 42 insertions(+)
create mode 100644 Documentation/arm/uefi.txt
diff --git a/Documentation/arm/00-INDEX b/Documentation/arm/00-INDEX
index 4978456..87e01d1 100644
--- a/Documentation/arm/00-INDEX
+++ b/Documentation/arm/00-INDEX
@@ -36,3 +36,6 @@ nwfpe/
- NWFPE floating point emulator documentation
swp_emulation
- SWP/SWPB emulation handler/logging description
+
+uefi.txt
+ - [U]EFI configuration and runtime services documentation
diff --git a/Documentation/arm/uefi.txt b/Documentation/arm/uefi.txt
new file mode 100644
index 0000000..5c48271
--- /dev/null
+++ b/Documentation/arm/uefi.txt
@@ -0,0 +1,39 @@
+The nomenclature EFI and UEFI are used interchangeably in this
document.
+
And the acronym expands to...?
+The implementation depends on receiving pointers to the UEFI memory
map
+and System Table in a Flattened Device Tree - so is only available
with
+CONFIG_OF.
+
+It (early) parses the FDT for the following parameters:
+- 'efi-system-table':
+ Physical address of the system table. (required)
+- 'efi-runtime-mmap':
+ Physical address of an EFI memory map, containing at least
+ the regions to be preserved. (required)
+- 'efi-runtime-mmap-size':
+ Size in bytes of the provided memory map. (required)
+- 'efi-mmap-desc-size':
+ Size of each descriptor in the memory map. (override default)
+- 'efi-mmap-desc-ver':
+ Memory descriptor format version. (override default)
+
+Since UEFI firmware on ARM systems are required to use a 1:1 memory
map
+even on LPAE-capable systems, the above fields are 32-bit regardless.
+
+It also depends on early_ioremap to parse the memory map and preserve
+the regions required for runtime services.
+
+For actually enabling [U]EFI support, enable:
+- CONFIG_EFI=y
+- CONFIG_EFI_VARS=y or m
+
+After the kernel has mapped the required regions into its address
space,
+a SetVirtualAddressMap() call is made into UEFI in order to update
+relocations. This call must be performed with all the code in a 1:1
+mapping. This implementation achieves this by temporarily disabling
the
+MMU for the duration of this call. This can only be done safely:
+- before secondary CPUs are brought online.
+- after early_initcalls have completed, sinze it uses
setup_mm_for_reboot().
Typo: since
+
+For verbose debug messages, specify 'uefi_debug' on the kernel
command
+line.
At a wild guess, this parses a memory descriptor table to find out
where the physical and device memory on an arm board live, according to
some standard? I'm guessing because the file never quite says what this
mechanism is _for_, just describes knobs on a black box...
(I can google, but it's a touch newbie-unfriendly. I tend to prefer
documentation that's aimed at people who _don't_ already know whatever
it is. Personal idiosyncrasy.)
Acked-by: Rob Landley <rob@xxxxxxxxxxx>
Rob--
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