Documentation: Add wake source info to device tree documentation
The device tree documentation was promoting using a GPIO wake event and a GPE wake event. We should only ever have one. This wasn't actually causing a problem because the wake bit was set on the `irq` property, but the IO-APIC can't actually wake the system, so it was a no-op. This change fixes up the markdown so it's formatted correctly, and also adds a section explaining what the different wake configurations are. BUG=b:243700486 TEST=mdformat Signed-off-by: Raul E Rangel <rrangel@chromium.org> Change-Id: Ifcdbd5371408784bf9b81c1ade90263de8c60e0f Reviewed-on: https://review.coreboot.org/c/coreboot/+/67385 Reviewed-by: Karthik Ramasubramanian <kramasub@google.com> Reviewed-by: Tim Van Patten <timvp@google.com> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This commit is contained in:
Raul E Rangel
Martin Roth
parent
ae7d8379a5
commit
0e9cc44d1b
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@ -8,7 +8,7 @@ device pci 15.0 on
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chip drivers/i2c/generic
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register "hid" = ""ELAN0000""
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register "desc" = ""ELAN Touchpad""
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register "irq" = "ACPI_IRQ_WAKE_LEVEL_LOW(GPP_A21_IRQ)"
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register "irq" = "ACPI_IRQ_LEVEL_LOW(GPP_A21_IRQ)"
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register "detect" = "1"
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register "wake" = "GPE0_DW0_21"
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device i2c 15 on end
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@ -39,7 +39,7 @@ Scope (\_SB.PCI0.I2C0)
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I2cSerialBusV2 (0x0015, ControllerInitiated, 400000,
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AddressingMode7Bit, "\\_SB.PCI0.I2C0",
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0x00, ResourceConsumer, , Exclusive, )
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Interrupt (ResourceConsumer, Level, ActiveLow, ExclusiveAndWake, ,, )
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Interrupt (ResourceConsumer, Level, ActiveLow, Exclusive, ,, )
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{
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0x0000002D,
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}
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@ -54,7 +54,7 @@ Scope (\_SB.PCI0.I2C0)
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}
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```
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You can see it generates _HID, _UID, _DDN, _STA, _CRS, _S0W, and _PRW
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You can see it generates \_HID, \_UID, \_DDN, \_STA, \_CRS, \_S0W, and \_PRW
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names/methods in the Device's scope.
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## Utilizing a device driver
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@ -88,7 +88,7 @@ be included in the ACPI table.
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register "hid" = ""ELAN0000""
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```
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This corresponds to **const char *hid** in the struct. In the ACPI ASL, it
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This corresponds to **const char \*hid** in the struct. In the ACPI ASL, it
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translates to:
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```
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@ -104,7 +104,7 @@ during enumeration in the OS.**
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register "desc" = ""ELAN Touchpad""
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```
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corresponds to **const char *desc** and in ASL:
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corresponds to **const char \*desc** and in ASL:
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```
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Name (_DDN, "ELAN Touchpad") // _DDN: DOS Device Name
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@ -115,7 +115,7 @@ corresponds to **const char *desc** and in ASL:
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It also adds the interrupt,
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```
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Interrupt (ResourceConsumer, Level, ActiveLow, ExclusiveAndWake, ,, )
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Interrupt (ResourceConsumer, Level, ActiveLow, Exclusive, ,, )
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{
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0x0000002D,
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}
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@ -124,23 +124,30 @@ It also adds the interrupt,
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which comes from:
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```
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register "irq" = "ACPI_IRQ_WAKE_LEVEL_LOW(GPP_A21_IRQ)"
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register "irq" = "ACPI_IRQ_LEVEL_LOW(GPP_A21_IRQ)"
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```
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The GPIO pin IRQ settings control the "Level", "ActiveLow", and
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"ExclusiveAndWake" settings seen above (level means it is a level-triggered
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interrupt as opposed to edge-triggered; active low means the interrupt is
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triggered when the signal is low).
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The IRQ settings control the "Trigger" and "Polarity" settings seen above (level
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means it is a level-triggered interrupt as opposed to
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edge-triggered; active low means the interrupt is triggered when the signal is
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low).
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Note that the ACPI_IRQ_WAKE_LEVEL_LOW macro informs the platform that the GPIO
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will be routed through SCI (ACPI's System Control Interrupt) for use as a wake
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source. Also note that the IRQ names are SoC-specific, and you will need to
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Also note that the IRQ names are SoC-specific, and you will need to
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find the names in your SoC's header file. The ACPI_* macros are defined in
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``src/arch/x86/include/acpi/acpi_device.h``.
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Using a GPIO as an IRQ requires that it is configured in coreboot correctly.
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This is often done in a mainboard-specific file named ``gpio.c``.
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AMD platforms don't have the ability to route GPIOs to the IO-APIC. Instead the
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GPIO controller needs to be used directly. You can do this by setting the
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`irq_gpio` register and using the `ACPI_GPIO_IRQ_X_X` macros.
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i.e.,
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```
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register "irq_gpio" = "ACPI_GPIO_IRQ_EDGE_LOW(GPIO_40)"
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```
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### detect
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The next register is:
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@ -180,6 +187,8 @@ through a GPE, #21 associated with DW0, which is set up in devicetree.cb from
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this example. The "21" indicates GPP_X21, where GPP_X is mapped onto DW0
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elsewhere in the devicetree.
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### device
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The last bit of the definition of that device includes:
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```
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@ -193,6 +202,65 @@ found on. In this example, this is I2C bus 0. This also determines the ACPI
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"Scope" that the device names and methods will live under, in this case
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"\_SB.PCI0.I2C0".
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## Wake sources
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The ACPI spec defines two methods to describe how a device can wake the system.
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Only one of these methods should be used, otherwise duplicate wake events will
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be generated.
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### Using GPEs as a wake source
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The `wake` property specified above is used to tell the ACPI subsystem that the
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device can use a GPE to wake the system. The OS can control whether to enable
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or disable the wake source by unmasking/masking off the GPE.
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The `GPIO` -> `GPE` mapping must be configured in firmware. On AMD platforms this is
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generally done by a mainboard specific `gpio.c` file that defines the GPIO
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using `PAD_SCI`. The `GPIO` -> `GPE` mapping is returned by the
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`soc_get_gpio_event_table` method that is defined in the SoC specific `gpio.c`
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file. On Intel platforms, you fill in the `pmc_gpe0_dw0`, `pmc_gpe0_dw1`, and
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`pmc_gpe0_dw2` fields in the devicetree to map 3 GPIO communities to `tier-1`
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GPEs (the rest are available as `tier-2` GPEs).
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Windows has a large caveat when using this method. If you use the `gpio_irq`
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property to define a `GpioInt` in the `_CRS`, and then use the `wake` property
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to define a `GPE`, Windows will
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[BSOD](https://github.com/MicrosoftDocs/windows-driver-docs/blob/staging/windows-driver-docs-pr/debugger/bug-check-0xa5--acpi-bios-error.md)
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complaining about an invalid ACPI configuration.
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> 0x1000D - A device used both GPE and GPIO interrupts, which is not supported.
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In order to avoid this error, you should use the `irq` property instead. AMD
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platforms don't support routing GPIOs to the IO-APIC, so this workaround isn't
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feasible. The other option is to use a wake capable GPIO as described below.
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### Using GPIO interrupts as a wake source
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The `ACPI_IRQ_WAKE_{EDGE,LEVEL}_{LOW,HIGH}` macros can be used when setting the
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`irq` or `gpio_irq` properties. This ends up setting `ExclusiveAndWake` or
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`SharedAndWake` on the `Interrupt` or `GpioInt` ACPI resource.
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This method has a few caveats:
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* On Intel and AMD platforms the IO-APIC can't wake the system. This means using
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the `ACPI_IRQ_WAKE_*` macros with the `irq` property won't actually wake the
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system. Instead you need to use the `gpio_irq` property, or a `GPE` as
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described above.
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* The OS needs to know how to enable the `wake` bit on the GPIO. For linux this
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means the platform specific GPIO controller driver must implement the
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`irq_set_wake` callback. For AMD systems this wasn't
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[implemented](https://github.com/torvalds/linux/commit/d62bd5ce12d79bcd6a6c3e4381daa7375dc21158)
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until linux v5.15. If the controller doesn't define this callback, it's
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possible for the firmware to manually set the `wake` bit on the GPIO. This is
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often done in a mainboard-specific file named `gpio.c`. This is not
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recommended because then it's not possible for the OS to disable the wake
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source.
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* As of
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[linux v6.0-rc5](https://github.com/torvalds/linux/releases/tag/v6.0-rc5),
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the ACPI subsystem doesn't take the interrupt `wake` bit into account when
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deciding on which power state to put the device in before suspending the
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system. This means that if you define a power resource for a device via
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`has_power_resource`, `enable_gpio`, etc, then the linux kernel will place the
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device into D3Cold. i.e., power off the device.
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## Other auto-generated names
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(see [ACPI specification
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@ -200,17 +268,19 @@ found on. In this example, this is I2C bus 0. This also determines the ACPI
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for more details on ACPI methods)
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### _S0W (S0 Device Wake State)
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_S0W indicates the deepest S0 sleep state this device can wake itself from,
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which in this case is ACPI_DEVICE_SLEEP_D3_HOT, representing _D3hot_.
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\_S0W indicates the deepest S0 sleep state this device can wake itself from,
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which in this case is `ACPI_DEVICE_SLEEP_D3_HOT`, representing _D3hot_.
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D3Hot means the `PR3` power resources are still on and the device is still
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responsive on the bus. For i2c devices this is generally the same state as `D0`.
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### _PRW (Power Resources for Wake)
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_PRW indicates the power resources and events required for wake. There are no
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### \_PRW (Power Resources for Wake)
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\_PRW indicates the power resources and events required for wake. There are no
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dependent power resources, but the GPE (GPE0_DW0_21) is mentioned here (0x15),
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as well as the deepest sleep state supporting waking the system (3), which is
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S3.
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### _STA (Status)
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The _STA method is generated automatically, and its values, 0xF, indicates the
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### \_STA (Status)
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The \_STA method is generated automatically, and its values, 0xF, indicates the
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following:
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Bit [0] – Set if the device is present.
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@ -218,8 +288,8 @@ following:
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Bit [2] – Set if the device should be shown in the UI.
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Bit [3] – Set if the device is functioning properly (cleared if device failed its diagnostics).
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### _CRS (Current resource settings)
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The _CRS method is generated automatically, as the driver knows it is an I2C
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### \_CRS (Current resource settings)
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The \_CRS method is generated automatically, as the driver knows it is an I2C
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controller, and so specifies how to configure the controller for proper
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operation with the touchpad.
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