Re: [PATCH v6 17/17] Documentation: ACPI for ARM64

[Hanjun Guo]

Hi Christoffer,

Sorry for the late reply, I got no answer yet but
with one question below.

On 2015å01æ20æ 04:33, Christoffer Dall wrote:
> Hi,
>
> On Sun, Jan 04, 2015 at 06:55:18PM +0800, Hanjun Guo wrote:
> > From: Graeme Gregory <graeme.gregory@xxxxxxxxxx>
> >
> > Add documentation for the guidelines of how to use ACPI
> > on ARM64.
> >
> > Reviewed-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
> > Signed-off-by: Graeme Gregory <graeme.gregory@xxxxxxxxxx>
> > Signed-off-by: Al Stone <al.stone@xxxxxxxxxx>
> > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> > ---
> >   Documentation/arm64/arm-acpi.txt | 327 +++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 327 insertions(+)
> >   create mode 100644 Documentation/arm64/arm-acpi.txt
> >
> > diff --git a/Documentation/arm64/arm-acpi.txt b/Documentation/arm64/arm-acpi.txt
> > new file mode 100644
> > index 0000000..21e7020
> > --- /dev/null
> > +++ b/Documentation/arm64/arm-acpi.txt
> > @@ -0,0 +1,327 @@
> > +ACPI on ARMv8 Servers
> > +---------------------
> > +ACPI can be used for ARMv8 general purpose servers designed to follow
> > +the ARM SBSA (Server Base System Architecture) and SBBR (Server Base
> > +Boot Requirements) specifications, currently available to those with
> > +an ARM login at http://silver.arm.com.
> > +
> > +The ARMv8 kernel implements the reduced hardware model of ACPI version
> > +5.1 and later.  Links to the specification and all external documents
> > +it refers to are managed by the UEFI Forum.  The specification is
> > +available at http://www.uefi.org/specifications and external documents
> > +can be found via http://www.uefi.org/acpi.
> > +
> > +If an ARMv8 system does not meet the requirements of the SBSA, or cannot
> > +be described using the mechanisms defined in the required ACPI specifications,
> > +then it is likely that Device Tree (DT) is more suitable than ACPI for the
> > +hardware.
> > +
> > +
> > +Relationship with Device Tree
> > +-----------------------------
> > +ACPI support in drivers and subsystems for ARMv8 should never be mutually
> > +exclusive with DT support at compile time.
> > +
> > +At boot time the kernel will only use one description method depending on
> > +parameters passed from the bootloader (including kernel bootargs).
> > +
> > +Regardless of whether DT or ACPI is used, the kernel must always be capable
> > +of booting with either scheme (in kernels with both schemes enabled at compile
> > +time).
> > +
> > +
> > +Booting using ACPI tables
> > +-------------------------
> > +The only defined method for passing ACPI tables to the kernel on ARMv8
> > +is via the UEFI system configuration table.
> > +
>
> This is a bit concerning for the approach we are currently taking to
> support ACPI on Xen [1].
>
> Background: Xen is a tiny hypervisor which cannot parse the DSDT or any
> other non-static table. Xen relies on Linux in Dom0 to manage most
> (basically everything except the GIC, serial port, SMMU, and timers)
> hardware resources and relies on Dom0 to parse the ACPI tables.
>
> While Xen itself is typically booted by UEFI and finds RSDP through the
> UEFI system table, Xen does NOT run another UEFI instance to boot Dom0
> nor does it pass through the presence of UEFI to Dom0 in any way.
> Instead, it just created a DT (with modifications concerning the
> hardware mentioned above) and boots Linux in Dom0 directly (on x86 any
> required UEFI call is performed through paravirtualized hypercalls).
>
> In the case of ACPI, Xen adds a property to the chosen node and
> populates it with the RDSP in Dom0's address space.  Patches have not

Sorry I'm not familiar with hypervisor, I have question here about
x86 on xen, how ACPI works on XEN for x86?

Thanks
Hanjun
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