Subject: [PATCH 19/19] Documentation: ACPI for ARM64

From: [email-masked] (Hanjun Guo)
Date: Fri, 25 Jul 2014 18:55:07 +0800

Hi Randy,

Thank you for your careful review comments, I will update it in next version :)

Best Regards
Hanjun

On 2014-7-25 4:42, Randy Dunlap wrote:
> On 07/24/2014 06:00 AM, Hanjun Guo wrote:
>> From: Graeme Gregory <[email-masked]>
>>
>> Add documentation for the guidelines of how to use ACPI
>> on ARM64.
>>
>> Signed-off-by: Graeme Gregory <[email-masked]>
>> Signed-off-by: Hanjun Guo <[email-masked]>
>> ---
>>  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)
> 
>                     .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
> 
>              XSDT;
> 
>> +only allow for 32bit addresses.
> 
>                   32-bit
> 
>> +
>> +DO NOT use the 32-bit address fields in the FADT, they are deprecated, 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.
> 
>                                    Recommendations
> 
>> +
>> +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.
> 
>                      If CONFIG_ACPI is not 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
> 
>                                                             avoided
> 
>> +the resources set to appropriate level by the firmware. If this is not possible
> 
>                                     levels
> 
>> +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
> 
>                                                                  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
> 
>                 (for example, UEFI)
> 
>> +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
> 
>                                                                  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 */
>> +		...
>> +	/* 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
> 
>             on a platform, ECRs
> 
>> +approval process.
>>
> 
>