linux-kernel - Re: [PATCH 0/6] Apple device properties

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Message-ID: <20160815115414.GE30909@codeblueprint.co.uk>
Date:	Mon, 15 Aug 2016 12:54:14 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Lukas Wunner <lukas@...ner.de>
Cc:	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andreas Noever <andreas.noever@...il.com>, x86@...nel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 0/6] Apple device properties

On Tue, 09 Aug, at 03:38:16PM, Lukas Wunner wrote:
> @@ -208,7 +201,10 @@ struct efi_config {
>  __pure const struct efi_config *__efi_early(void);
>  
>  #define efi_call_early(f, ...)						\
> -	__efi_early()->call(__efi_early()->f, __VA_ARGS__);
> +	__efi_early()->call(__efi_early()->is64 ?			\
> +	((efi_boot_services_64_t *)__efi_early()->boot_services)->f :	\
> +	((efi_boot_services_32_t *)__efi_early()->boot_services)->f,	\
> +						       __VA_ARGS__);
>  

You cannot use pointers from the firmware directly in mixed mode
because the kernel is compiled for 64-bits but the firmware is using
32-bit addresses, so dereferencing a pointer causes a 64-bit load.

That's the reason we deconstruct the tables and copy the addresses
from the last level - so we don't have to jump through multiple
pointers.