On Friday, January 10, 2014 03:52:15 PM al.stone@xxxxxxxxxx wrote: > From: Al Stone <al.stone@xxxxxxxxxx> > > 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. > This mode was first introduced in the ACPI 5.0 specification, but because > it is so much simpler and reduces the size of the object code needed to > support ACPI, it is likely to be used more often in the near future. > > 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. For ARM/ARM64, hardware reduced ACPI > should be the only mode used; legacy mode would require modifications > to SoCs in order to provide several x86-specific hardware features (e.g., > an NMI and SMI support). > > We set ACPI_REDUCED_HARDWARE to TRUE in the ACPICA source 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 > > Even though support for X86 in hardware reduced mode is possible, it > is NOT enabled. Extensive effort has gone into the Linux kernel so that > there is a single kernel image than can run on all x86 hardware; the kernel > changes run-time behavior to adapt to the hardware being used. This is not > currently possible with the existing ACPICA infrastructure but only presents > a problem on achitectures supporting both hardware-reduced and legacy modes > of ACPI -- i.e., on x86 only. > > The problem with the current ACPICA code base is that if one builds legacy > ACPI (a proper superset of hardware-reduced), the kernel can run in hardware- > reduced with the proper ACPI tables, but there is still ACPICA code that could > be executed even though it is not allowed by the specification. If one builds > a hardware-reduced only ACPI, the kernel cannot run with ACPI tables that are > for legacy mode. To ensure compliance with ACPI, one must therefore build > two separate kernels. Once this problem has been properly fixed, we can then > enable x86 hardware-reduced mode and use a single kernel. > > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx> > Signed-off-by: Al Stone <al.stone@xxxxxxxxxx> > --- > drivers/acpi/Kconfig | 12 ++++++++++++ > include/acpi/platform/aclinux.h | 6 ++++++ > 2 files changed, 18 insertions(+) > > diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig > index 4770de5..75dd38a 100644 > --- a/drivers/acpi/Kconfig > +++ b/drivers/acpi/Kconfig > @@ -343,6 +343,18 @@ config ACPI_BGRT > data from the firmware boot splash. It will appear under > /sys/firmware/acpi/bgrt/ . > > +config ACPI_REDUCED_HARDWARE_ONLY > + bool "Hardware-reduced ACPI support only" > + depends on !X86 && !IA64 || EXPERT > + help > + This config item changes the way the ACPI code is built. When this > + option is selected, the kernel will use a specialized version of > + ACPICA that ONLY supports the ACPI "reduced hardware" mode. The > + resulting kernel will be smaller but it will also be restricted to > + running in ACPI reduced hardware mode ONLY. > + > + If you are unsure what to do, do not enable this option. I'm still not exactly convinced this is the best way to do that. In particular, I wonder if it would be viable to make it disabled by default and then make the interested architectures do select ACPI_REDUCED_HARDWARE_ONLY if ACPI in their top-level Kconfig files? > + > source "drivers/acpi/apei/Kconfig" > > config ACPI_EXTLOG > diff --git a/include/acpi/platform/aclinux.h b/include/acpi/platform/aclinux.h > index 28f4f4d..7d71f08 100644 > --- a/include/acpi/platform/aclinux.h > +++ b/include/acpi/platform/aclinux.h > @@ -52,6 +52,12 @@ > > #ifdef __KERNEL__ > > +/* Compile for reduced hardware mode only with this kernel config */ > + > +#ifdef CONFIG_ACPI_REDUCED_HARDWARE_ONLY > +#define ACPI_REDUCED_HARDWARE 1 > +#endif > + > #include <linux/string.h> > #include <linux/kernel.h> > #include <linux/ctype.h> > -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
