linux-kernel - Re: [PATCH 1/4] Documentation: arm: [U]EFI runtime services

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Message-ID: <51C9E58E.5050004@codeaurora.org>
Date:	Tue, 25 Jun 2013 14:46:38 -0400
From:	Christopher Covington <cov@...eaurora.org>
To:	Leif Lindholm <leif.lindholm@...aro.org>
CC:	linux-arm-kernel@...ts.infradead.org, linux-efi@...r.kernel.org,
	patches@...aro.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, matt.fleming@...el.com,
	tglx@...utronix.de, hpa@...ux.intel.com
Subject: Re: [PATCH 1/4] Documentation: arm: [U]EFI runtime services

On 06/25/2013 02:11 PM, Leif Lindholm wrote:
> This patch provides documentation of the [U]EFI runtime services and
> configuration features.
> 
> Signed-off-by: Leif Lindholm <leif.lindholm@...aro.org>
> ---
>  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.
> +
> +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().

since

> +
> +For verbose debug messages, specify 'uefi_debug' on the kernel command
> +line.
> 

Christopher

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