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

[Grant Likely]

Hi Hanjun,

Okay, so after talking with Al and Graeme on IRC, I think I understand
what is going on. The fact that ACPICA doesn't allow for both normal and
hardware reduced support in the same build is a very big problem.
However, it isn't a problem for ARM since we'll never support
non-hardware reduced mode. The x86 folks need to work that out when/if
they ever add support for hardware reduced mode.

So I would say the thing to do is only allow hardware reduced mode to be
enabled on ARM, and make it ultra clear in the config text that it
cannot be supported on x86 before ACPICA is fixed.

g.

On Tue, 10 Dec 2013 23:05:03 +0800, Hanjun Guo <hanjun.guo at linaro.org> wrote:
> On 2013年12月10日 20:37, Grant Likely wrote:
> > 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?
> 
> Both yes. ACPICA supports reduced hardware mode when
> ACPI_REDUCED_HARWARE is TRUE at compile time. There is
> no way to support both normal ACPI and hardware reduced
> ACPI with single binary image for now.
> 
> > If so, then this is a big problem. Enabling
> > the hardware reduced feature should *not* break normal ACPI usage.
> 
> It will break normal ACPI usage but it is ok I think. Since
> lots of features are not supported in the hardware in hardware
> reduced mode, and normal ACPI will not run probably such as
> leading kernel panic when refer to some registers which are not
> exist on reduced hardware, we should introduce this kernel
> config and modify the ACPI drivers to avoid such failures.
> 
> Thanks
> Hanjun
>