linux-kernel - Re: [PATCH 19/19] Documentation: ACPI for ARM64

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Date:	Tue, 29 Jul 2014 12:07:47 +0200
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Naresh Bhat <naresh.bhat@...aro.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Mark Brown <broonie@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Lv Zheng <lv.zheng@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Robert Moore <robert.moore@...el.com>,
	linux-acpi@...r.kernel.org, Grant Likely <grant.likely@...aro.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Arnd Bergmann <arnd@...db.de>,
	Marc Zyngier <marc.zyngier@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	linaro-acpi-private@...aro.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	Graeme Gregory <graeme.gregory@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, Sudeep Holla <Sudeep.Holla@....com>
Subject: Re: [PATCH 19/19] Documentation: ACPI for ARM64

On Thu, Jul 24, 2014 at 02:19:14PM -0700, Randy Dunlap wrote:
> On 07/24/2014 02:16 PM, Naresh Bhat wrote:
> > 
> > On 24 July 2014 18:30, Hanjun Guo <hanjun.guo@...aro.org <mailto:hanjun.guo@...aro.org>> wrote:
> > 
> >     From: Graeme Gregory <graeme.gregory@...aro.org <mailto:graeme.gregory@...aro.org>>
> > 
> >     Add documentation for the guidelines of how to use ACPI
> >     on ARM64.
> > 
> >     Signed-off-by: Graeme Gregory <graeme.gregory@...aro.org <mailto:graeme.gregory@...aro.org>>
> >     Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org <mailto:hanjun.guo@...aro.org>>
> >     ---
> >      Documentation/arm64/arm-acpi.txt |  240 ++++++++++++++++++++++++++++++++++++++
> >      1 file changed, 240 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..12cd550
> >     --- /dev/null
> >     +++ b/Documentation/arm64/arm-acpi.txt
> >     @@ -0,0 +1,240 @@
> >     +ACPI on ARMv8 Servers
> >     +---------------------
> >     +
> >     +ACPI will be used for ARMv8 general purpose servers designed to follow
> >     +the SBSA specification (currently available to people with an ARM login at
> >     +http://silver.arm.com)
> >     +
> >     +The implemented ACPI version is 5.1 + errata as released by the UEFI Forum,
> >     +which is available at <http://www.uefi.org/acpi/specs>.
> >     +
> >     +If the machine does not meet these requirements then it is likely that Device
> >     +Tree (DT) is more suitable 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.
> >     +
> >     +Regardless of whether DT or ACPI is used, the kernel must always be capable
> >     +of booting with either scheme.
> >     +
> >     +When booting using ACPI tables the /chosen node in DT will still be parsed
> >     +to extract the kernel command line and initrd path. No other section of
> >     +the DT will be used.
> >     +
> >     +Booting using ACPI tables
> >     +-------------------------
> >     +
> >     +Currently, the only defined method to pass ACPI tables to the kernel on ARMv8
> >     +is via the UEFI system configuration table.
> >     +
> >     +The UEFI implementation MUST set the ACPI_20_TABLE_GUID to point to the
> >     +RSDP table (the table with the ACPI signature "RSD PTR ").
> >     +
> >     +The pointer to the RSDP table will be retrieved from EFI by the ACPI core.
> >     +
> >     +Processing of ACPI tables may be disabled by passing acpi=off on the kernel
> >     +command line.
> >     +
> >     +DO use an XSDT, RSDTs are deprecated and should not be used on arm64. They
> >     +only allow for 32bit addresses.
> >     +
> >     +DO NOT use the 32-bit address fields in the FADT, they are deprecated, the
> >     +64-bit alternatives MUST be used.
> >     +
> >     +The minimum set of tables MUST include RSDP, XSDT, FACS, FADT, DSDT, MADT
> >     +and GTDT. If PCI is used the MCFG table MUST also be present.
> >     +
> >     +ACPI Detection
> >     +--------------
> >     +
> >     +Drivers should determine their probe() type by checking for ACPI_HANDLE,
> >     +or .of_node, or other information in the device structure. This is
> >     +detailed further in the "Driver Recomendations" section.
> >     +
> >     +If the presence of ACPI needs to be detected at runtime, then check the value
> >     +of acpi_disabled. If CONFIG_ACPI not being set acpi_disabled will always be 1.
> >     +
> >     +Device Enumeration
> >     +------------------
> >     +
> >     +Device descriptions in ACPI should use standard recognised ACPI interfaces.
> > 
> > 
> > recognized
> 
> Yeah, I saw all of these also, but we accept British or American spelling of these words.
> 
Would be good to check for a consistent spelling in this doc though.

-Christoffer
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