On 07/24/2014 02:16 PM, Naresh Bhat wrote: > > On 24 July 2014 18:30, Hanjun Guo <hanjun.guo@xxxxxxxxxx <mailto:hanjun.guo@xxxxxxxxxx>> wrote: > > From: Graeme Gregory <graeme.gregory@xxxxxxxxxx <mailto:graeme.gregory@xxxxxxxxxx>> > > Add documentation for the guidelines of how to use ACPI > on ARM64. > > Signed-off-by: Graeme Gregory <graeme.gregory@xxxxxxxxxx <mailto:graeme.gregory@xxxxxxxxxx>> > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx <mailto:hanjun.guo@xxxxxxxxxx>> > --- > 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. > > > +These are far simpler than the information provided via Device Tree. Drivers > +should take into account this simplicity and work with sensible defaults. > + > +On no account should a Device Tree attempt to be replicated in ASL using such > +constructs as Name(KEY0, "Value1") type constructs. Additional driver specific > +data should be passed in the appropriate _DSM (ACPI Section 9.14.1) method or > +_DSD (ACPI Section 6.2.5). This data should be rare and not OS specific. > + > +Common _DSD bindings should be submitted to ASWG to be included in the > +document :- > + > +http://www.uefi.org/sites/default/files/resources/_DSD-implementation-guide-toplevel.htm > + > +TODO: Clarification and examples from Juno implementation. > + > +Programmable Power Control Resources > +------------------------------------ > + > +Programmable power control resources include such resources as voltage/current > +providers (regulators) and clock sources. > + > +For power control of these resources they should be represented with Power > +Resource Objects (ACPI Section 7.1). The ACPI core will then handle correctly > +enabling/disabling of resources as they are needed. > + > +There exists in the ACPI 5.1 specification no standard binding for these objects > +to enable programmable levels or rates so this should be avoid if possible and > +the resources set to appropriate level by the firmware. If this is not possible > +then any manipulation should be abstracted in ASL. > + > +Each device in ACPI has D-states and these can be controlled through > +the optional methods _PS0..._PS3 where _PS0 is full on and _PS3 is full off. > + > +If either _PS0 or _PS3 is implemented, then the other method must also be > +implemented. > + > +If a device requires usage or setup of a power resource when on, the ASL > +should organise that it is allocated/enabled using the _PS0 method. > > > organize > > + > +Resources allocated/enabled in the _PS0 method should be disabled/de-allocated > +in the _PS3 method. > + > +Such code in _PS? methods will of course be very platform specific but > +should allow the driver to operate the device without special non standard > +values being read from ASL. Further, abstracting the use of these resources > +allows hardware revisions without requiring updates to the kernel. > + > +TODO: Clarification and examples from Juno implementation. > + > +Clocks > +------ > + > +Like clocks that are part of the power resources there is no standard way > +to represent a clock tree in ACPI 5.1 in a similar manner to how it is > +described in DT. > + > +Devices affected by this include things like UARTs, SoC driven LCD displays, > +etc. > + > +The firmware for example UEFI should initialise these clocks to fixed working > > > initialize > > > +values before the kernel is executed. If a driver requires to know rates of > +clocks set by firmware then they can be passed to kernel using _DSD. > + > +example :- > + > +Device (CLK0) { > + ... > + > + Name (_DSD, Package() { > + ToUUID("XXXXX"), > + Package() { > + Package(2) {"#clock-cells", 0}, > + Package(2) {"clock-frequency", "10000"} > + } > + }) > + > + ... > +} > + > +Device (USR1) { > + ... > + > + Name (_DSD, Package() { > + ToUUID("XXXXX"), > + Package() { > + Package(2) {"clocks", Package() {1, ^CLK0}}}, > + } > + }) > + > + ... > +} > + > +Driver Recommendations > +---------------------- > + > +DO NOT remove any FDT handling when adding ACPI support for a driver, different > +systems may use the same device. > + > +DO try and keep complex sections of ACPI and DT functionality seperate. This > > > separate > > > +may mean a patch to break out some complex DT to another function before > +the patch to add ACPI. This may happen in other functions but is most likely > +in probe function. This gives a clearer flow of data for reviewing driver > +source. > + > +probe() :- > + > +TODO: replace this with a specific real example from Juno? > + > +static int device_probe_dt(struct platform_device *pdev) > +{ > + /* DT specific functionality */ > + ... > +} > + > +static int device_probe_acpi(struct platform_device *pdev) > +{ > + /* ACPI specific functionality */ > + ... > +} > + > +static int device_probe(stuct platform_device *pdev) > +{ > + ... > + acpi_handle handle = ACPI_HANDLE(&pdev->dev); > + struct device_node node = pdev->dev.of_node; > + ... > + > + if (node) > + ret = device_probe_dt(pdev); > + else if (handle) > + ret = device_probe_acpi(pdev); > + else > + /* other initialisation */ > > > initialization > > > + ... > + /* Continue with any generic probe operations */ > + ... > +} > + > +DO keep the MODULE_DEVICE_TABLE entries together in the driver to make it clear > +the different names the driver is probed for, both from DT and from ACPI. > + > +module device tables :- > + > +static struct of_device_id virtio_mmio_match[] = { > + { .compatible = "virtio,mmio", }, > + {}, > +}; > +MODULE_DEVICE_TABLE(of, virtio_mmio_match); > + > +static const struct acpi_device_id virtio_mmio_acpi_match[] = { > + { "LNRO0005", }, > + { } > +}; > +MODULE_DEVICE_TABLE(acpi, virtio_mmio_acpi_match); > + > +TODO: Add any other helpful rules that develop from Juno ACPI work. > + > +ASWG > +---- > + > +The following areas are not yet well defined for ARM in the current ACPI > +specification and are expected to be worked through in the UEFI ACPI > +Specification Working Group (ASWG) <http://www.uefi.org/workinggroups>. > +Participation in this group is open to all UEFI members. > + > + - ACPI based CPU topology > + - ACPI based Power management > + - CPU idle control based on PSCI > + - CPU performance control (CPPC) > + > +No code shall be accepted into the kernel unless it complies with the released > +standards from UEFI ASWG. If there are features missing from ACPI to make it > +function on a platform ECRs should be submitted to ASWG and go through the > +approval process. > -- > 1.7.9.5 > > -- ~Randy -- 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
