ACPI/Board-EC interaction

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Revision as of 01:48, 10 April 2014 by MrNuke (talk | contribs) (The mainboard namespace method)
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Documentation is now handled by the same processes we use for code: Add something to the Documentation/ directory in the coreboot repo, and it will be rendered to https://doc.coreboot.org/. Contributions welcome!

This page details the required interface and implementation details for connecting embedded controller ASL files to mainboard ASL files. Implementing this specification is mandatory for every new mainboard/EC added to the tree.

WARNING! The rules presented here are still a work-in-progress and should not yet be taken as as mandatory. However, if you are implementing a new EC, mainboard, or are interested in refactoring existing ASL files, you should join in the conversation and get this specification finalized.

EC ASL files should be self-contained, and not depend on the specific chipset or mainboard. As a result all variables and methods which are used must be standardized to foster interoperability and modularity. This specification details how to achieve those points.

System Resources

All ECs are assumed to use IO ports 0x62 and 0x66 for data/commands. If the EC also serves as a keyboard controller, it is assumed to use ports 0x60 and 0x64. I/O port accesses to these ports must be directed to the bus to which the EC is connected. These need not be individually documented.

If the EC uses different ports, or needs other system resources, those must be documented in src/ec/vendor/model/documentation.txt

Defined constants

  • EC_SCI_GPE
    • The general purpose event (GPE) corresponding to the EC SCI line.

Hotkey event methods

Two proposals exist:

The hammer method

Define a set of common ACPI method names which the mainboard code should define, and the EC code can always use.

The mainboard must #define these to an existing method. The actual ASL methods must not use these long names in ASL. The "MB_" prefix indicates that the mainboard is providing these methods.

Notice that these methods are only called on hotkey events. As such, unless the user has really fast fingers, there isn't a huge ACPI overhead as opposed to setting/clearing the needed bits directly in the caller.

  • MB_TOGGLE_WLAN() or MB_TOGGLE_WIRELESS() (TODO: only one method should be defined!!!)
    • Toggle wireless LAN on and off, or wireless LAN and bluetooth (respectively). EC calls this on hotkey events.
  • MB_INCREASE_BRIGHTNESS() and MB_DECREASE_BRIGHTNESS()
    • Increase or decrease screen brightness. EC calls this on hotkey events.
  • MB_SWITCH_DISPLAY()
    • Switch the active display. EC calls this on hotkey events.
  • MB_NOTIFY_POWER_EVENT()
    • Handle power state notifications and notify CPU device objects to re-evaluate their _PPC and _CST tables.

For example:

/* Brightness up hotkey event */
Method (_Q11) {                 
        MB_INCREASE_BRIGHTNESS();
}

/* Brightness down hotkey event */
Method (_Q12) {                 
        MB_DECREASE_BRIGHTNESS();
}

/* Wireless on/off hotkey event */
Method (_Q1C) {                 
        MB_TOGGLE_WIRELESS();
}

The mainboard handler method

Provide a generic mainboard "EC event" method that any EC _Qxx could call and pass the event ID to. The event ID is a standard defined event ID , greater than 255 so as not to conflict with possible Qxx IDs. This limits the permutations of mainboard EC event handlers and gives the flexibility to pass all the various EC events to the mainboard for handling.

For example:

#define EC_EVENT_LID_CLOSED 0x100

In the EC ASL:

/* lid closed */
Method (_Q01) {                 
        \_SB.MBEC (EC_EVENT_LID_CLOSED)
}

And the mainboard handler could look like:

Scope (\_SB)
{
        /* mainboard event handler */
        Method (MBEC, 1, Serialized) {
        Switch (ToInteger (Arg0)) {
                Case (EC_EVENT_LID_CLOSED) { ... }
                Case (EC_EVENT_...) { ... }
        }
}

The mainboard namespace method

Similar to the mainboard handler method, but handlers are placed in a special namespace, and the names of the methods are standardized.

Device (MB) {
	/* Lid open */
	Method (LIDO) { /* Stub */ }
	/* Lid closed */
	Method (LIDC) { /* Stub */}
	/* Increase brightness */
	Method (BRTU) { /* Stub */ }
	/* Decrease brightness */
	Method (BRTD) { /* Stub */ }
 	/* Switch display */
	Method (DSPS) { /* Stub */ }
	/* Toggle wireless */
	Method (WLTG) { /* Stub */ }
	/* Decrease brightness */
	Method (LIDS)  { /* Stub */ }
}

But even in this form there needs to be a generic method for all the special cases...

EC-specific extensions

The EC may provide specific extensions to this specifications. However, any such extension must be fully documented in src/ec/vendor/model/documentation.txt. The EC must be able to function properly even if the mainboard does not define or use such extensions.