From: Graeme Gregory <graeme.gregory@xxxxxxxxxx> Add documentation for the guidelines of how to use ACPI on ARM64. Signed-off-by: Graeme Gregory <graeme.gregory@xxxxxxxxxx> Signed-off-by: Hanjun Guo <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. +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. + +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 +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 +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 */ + ... + /* 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 -- 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
