Messages in this thread | | | Date | Wed, 31 Dec 2014 16:34:46 +0800 | From | Hanjun Guo <> | Subject | Re: [PATCH v5 18/18] Documentation: ACPI for ARM64 |
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On 2014年12月31日 04:13, ashwinc@codeaurora.org wrote: > Hi Hanjun, > > Overall the document looks good to us. Some minor clarifications below. > >> ---------- Forwarded message ---------- >> From: Graeme Gregory <graeme.gregory@linaro.org> >> >> Add documentation for the guidelines of how to use ACPI >> on ARM64. >> >> Signed-off-by: Graeme Gregory <graeme.gregory@linaro.org> >> Signed-off-by: Al Stone <al.stone@linaro.org> >> Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org> >> --- >> Documentation/arm64/arm-acpi.txt | 323 >> ++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 323 insertions(+) >> create mode 100644 Documentation/arm64/arm-acpi.txt >> > > [..] > >> +Relationship with Device Tree >> +----------------------------- > > [..] > >> +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. > > Is this still true?
No, we can booting the ACPI system in EFI stub without dtb. Catalin also pointed out this issue, I will remove this paragraph.
> > >> +Programmable Power Control Resources >> +------------------------------------ >> +Programmable power control resources include such resources as >> voltage/current >> +providers (regulators) and clock sources. >> + >> +The kernel assumes that power control of these resources is represented >> with >> +Power Resource Objects (ACPI section 7.1). The ACPI core will then >> handle >> +correctly enabling and disabling resources as they are needed. In order >> to >> +get that to work, ACPI assumes each device has defined D-states and that >> these >> +can be controlled through the optional ACPI methods _PS0, _PS1, _PS2, and >> _PS3; >> +in ACPI, _PS0 is the method to invoke to turn a device full on, and _PS3 >> is for >> +turning a device full off. >> + >> +The kernel ACPI code will also assume that the _PS? methods follow the >> normal >> +ACPI rules for such methods: >> + >> + -- 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 organize that it is allocated/enabled using the _PS0 method. >> + >> + -- Resources allocated or enabled in the _PS0 method should be >> disabled >> + or de-allocated in the _PS3 method. >> + >> + -- Firmware will leave the resources in a reasonable state before >> handing >> + over control to the kernel. >> + > > We found this section could be improved a bit by explicitly calling out > the options for handling device PM. Platform vendor has two choices. > Resources can be managed in _PSx routine which gets called on entry to Dx. > Or they can be declared separately as power resources with their own _ON > and _OFF methods. They are then tied back to D-states for a particular > device via _PRx which specifies which power resources a device needs to be > on while in Dx. Kernel then tracks number of devices using a power > resource and calls _ON/_OFF as needed.
Good point, this exactly what ACPI spec says, we need to update this paragraph a little bit.
> >> +Such code in _PS? methods will of course be very platform specific. But, >> +this allows the driver to abstract out the interface for operating the >> device >> +and avoid having to read special non-standard values from ACPI tables. >> Further, >> +abstracting the use of these resources allows the hardware to change over >> time >> +without requiring updates to the driver. >> + > > I think its been mentioned in the past and you planned to add it here: we > should explicitly state that with ACPI, the kernel clock/vreg framework > are not expected to be used at all. > >> + >> +Clocks >> +------ >> +ACPI makes the assumption that clocks are initialized by the firmware -- >> +UEFI, in this case -- to some working value before control is handed over >> +to the kernel. This has implications for devices such as UARTs, or SoC >> +driven LCD displays, for example. >> + >> +When the kernel boots, the clock is assumed to be set to reasonable >> +working value. If for some reason the frequency needs to change -- e.g., >> +throttling for power management -- the device driver should expect that >> +process to be abstracted out into some ACPI method that can be invoked > > Exception to this is CPU clocks where CPPC provides a much richer > interface than just blindly invoking some method. > >> +(please see the ACPI specification for further recommendations on >> standard >> +methods to be expected). If is not, there is no direct way for ACPI to >> +control the clocks. >> + >> + > > [..] > >> +ASWG >> +---- >> +The following areas are not yet fully defined for ARM in the 5.1 version >> +of the ACPI specification and are expected to be worked through in the >> +UEFI ACPI Specification Working Group (ASWG): >> + >> + -- ACPI based CPU topology >> + -- ACPI based Power management > > Should clarify this to idle management rather than generic power management.
and I think it is CPU idle specific here, right?
> >> + -- CPU idle control based on PSCI >> + -- CPU performance control (CPPC) > > There is no ongoing work on CPPC. Additional enhancements may be explored > in the future, but spec is viable as is.
will remove it.
Thanks for reviewing it!
Hanjun
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