[Linaro-acpi] [PATCH v3 1/5] ACPI: introduce CONFIG_ACPI_REDUCED_HARDWARE to enable this ACPI mode

[Grant Likely]

On Wed,  4 Dec 2013 14:22:03 -0700, al.stone at linaro.org wrote:
> From: Al Stone <al.stone at linaro.org>
> 
> To enable the hardware reduced mode of ACPI on some platforms (such as
> ARM), we need to modify the kernel code and set ACPI_REDUCED_HARDWARE
> to TRUE in the ACPICA source.
> 
> This can be done more resonably by introducing a kernel config item
> to enable/disable ACPI_REDUCED_HARDWARE.  We can then change the kernel
> config instead of having to modify the kernel source directly to enable
> the reduced hardware mode of ACPI.
> 
> Lv Zheng suggested that this configuration item does not belong in ACPICA,
> the upstream source for much of the ACPI internals, but rather to the
> Linux kernel itself.  Hence, we introduce this flag so that we can make
> ACPI_REDUCED_HARDWARE configurable.  For the details of the discussion,
> please refer to: http://www.spinics.net/lists/linux-acpi/msg46369.html
> 
> Support for X86 in hardware reduced mode is also provided to make it
> simpler to debug this mode, and to provide for probable use in such
> products.  Hardware reduced mode, despite the name, exists primarily
> to allow newer platforms to use a much simpler form of ACPI that does
> not require supporting the legacy of previous versions of the specification,
> and is likely to be used more often in the near future as a result.
> 
> Signed-off-by: Hanjun Guo <hanjun.guo at linaro.org>
> Signed-off-by: Al Stone <al.stone at linaro.org>
> ---
>  drivers/acpi/Kconfig            | 8 ++++++++
>  include/acpi/platform/aclinux.h | 6 ++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index 5d92485..66e6bb2 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -343,6 +343,14 @@ config ACPI_BGRT
>  	  data from the firmware boot splash. It will appear under
>  	  /sys/firmware/acpi/bgrt/ .
>  
> +config ACPI_REDUCED_HARDWARE
> +	bool "Hardware-reduced ACPI support"
> +	depends on X86 || ARM || ARM64
> +	help
> +	This config adds support for Hardware-reduced ACPI. When this option
> +	is selected, will generate a specialized version of ACPICA that ONLY
> +	supports the ACPI "reduced hardware".
> +
>  source "drivers/acpi/apei/Kconfig"
>  
>  config ACPI_EXTLOG
> diff --git a/include/acpi/platform/aclinux.h b/include/acpi/platform/aclinux.h
> index 28f4f4d..a33f502 100644
> --- a/include/acpi/platform/aclinux.h
> +++ b/include/acpi/platform/aclinux.h
> @@ -52,6 +52,12 @@
>  
>  #ifdef __KERNEL__
>  
> +/* Compile for reduced hardware mode if requested for this kernel config */
> +
> +#ifdef CONFIG_ACPI_REDUCED_HARDWARE
> +#define ACPI_REDUCED_HARDWARE 1
> +#endif

Will this change the way ACPICA is compiled? Will it disable
non-hardware-reduced mode? If so, then this is a big problem. Enabling
the hardware reduced feature should *not* break normal ACPI usage.

g.