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>

1 files changed, 92 insertions, 22 deletions

diff --git a/Documentation/drivers/dt_entries.md b/Documentation/drivers/dt_entries.md
index 9df965fa0d..dd54846e95 100644
--- a/Documentation/drivers/dt_entries.md
+++ b/Documentation/drivers/dt_entries.md
@@ -8,7 +8,7 @@ device pci 15.0 on
 	chip drivers/i2c/generic
 		register "hid" = ""ELAN0000""
 		register "desc" = ""ELAN Touchpad""
-		register "irq" = "ACPI_IRQ_WAKE_LEVEL_LOW(GPP_A21_IRQ)"
+		register "irq" = "ACPI_IRQ_LEVEL_LOW(GPP_A21_IRQ)"
 		register "detect" = "1"
 		register "wake" = "GPE0_DW0_21"
 		device i2c 15 on end
@@ -39,7 +39,7 @@ Scope (\_SB.PCI0.I2C0)
             I2cSerialBusV2 (0x0015, ControllerInitiated, 400000,
                 AddressingMode7Bit, "\\_SB.PCI0.I2C0",
                 0x00, ResourceConsumer, , Exclusive, )
-            Interrupt (ResourceConsumer, Level, ActiveLow, ExclusiveAndWake, ,, )
+            Interrupt (ResourceConsumer, Level, ActiveLow, Exclusive, ,, )
             {
                 0x0000002D,
             }
@@ -54,7 +54,7 @@ Scope (\_SB.PCI0.I2C0)
 }
 ```
 
-You can see it generates _HID, _UID, _DDN, _STA, _CRS, _S0W, and _PRW
+You can see it generates \_HID, \_UID, \_DDN, \_STA, \_CRS, \_S0W, and \_PRW
 names/methods in the Device's scope.
 
 ## Utilizing a device driver
@@ -88,7 +88,7 @@ be included in the ACPI table.
     register "hid" = ""ELAN0000""
 ```
 
-This corresponds to **const char *hid** in the struct.  In the ACPI ASL, it
+This corresponds to **const char \*hid** in the struct.  In the ACPI ASL, it
 translates to:
 
 ```
@@ -104,7 +104,7 @@ during enumeration in the OS.**
     register "desc" = ""ELAN Touchpad""
 ```
 
-corresponds to **const char *desc** and in ASL:
+corresponds to **const char \*desc** and in ASL:
 
 ```
     Name (_DDN, "ELAN Touchpad") // _DDN: DOS Device Name
@@ -115,7 +115,7 @@ corresponds to **const char *desc** and in ASL:
 It also adds the interrupt,
 
 ```
-    Interrupt (ResourceConsumer, Level, ActiveLow, ExclusiveAndWake, ,, )
+    Interrupt (ResourceConsumer, Level, ActiveLow, Exclusive, ,, )
     {
         0x0000002D,
     }
@@ -124,23 +124,30 @@ It also adds the interrupt,
 which comes from:
 
 ```
-    register "irq" = "ACPI_IRQ_WAKE_LEVEL_LOW(GPP_A21_IRQ)"
+    register "irq" = "ACPI_IRQ_LEVEL_LOW(GPP_A21_IRQ)"
 ```
 
-The GPIO pin IRQ settings control the "Level", "ActiveLow", and
-"ExclusiveAndWake" settings seen above (level means it is a level-triggered
-interrupt as opposed to edge-triggered; active low means the interrupt is
-triggered when the signal is low).
+The IRQ settings control the "Trigger" and "Polarity" settings seen above (level
+means it is a level-triggered interrupt as opposed to
+edge-triggered; active low means the interrupt is triggered when the signal is
+low).
 
-Note that the ACPI_IRQ_WAKE_LEVEL_LOW macro informs the platform that the GPIO
-will be routed through SCI (ACPI's System Control Interrupt) for use as a wake
-source.  Also note that the IRQ names are SoC-specific, and you will need to
+Also note that the IRQ names are SoC-specific, and you will need to
 find the names in your SoC's header file.  The ACPI_* macros are defined in
 ``src/arch/x86/include/acpi/acpi_device.h``.
 
 Using a GPIO as an IRQ requires that it is configured in coreboot correctly.
 This is often done in a mainboard-specific file named ``gpio.c``.
 
+AMD platforms don't have the ability to route GPIOs to the IO-APIC. Instead the
+GPIO controller needs to be used directly. You can do this by setting the
+`irq_gpio` register and using the `ACPI_GPIO_IRQ_X_X` macros.
+
+i.e.,
+```
+register "irq_gpio" = "ACPI_GPIO_IRQ_EDGE_LOW(GPIO_40)"
+```
+
 ### detect
 
 The next register is:
@@ -180,6 +187,8 @@ through a GPE, #21 associated with DW0, which is set up in devicetree.cb from
 this example.  The "21" indicates GPP_X21, where GPP_X is mapped onto DW0
 elsewhere in the devicetree.
 
+### device
+
 The last bit of the definition of that device includes:
 
 ```
@@ -193,6 +202,65 @@ found on.  In this example, this is I2C bus 0.  This also determines the ACPI
 "Scope" that the device names and methods will live under, in this case
 "\_SB.PCI0.I2C0".
 
+## Wake sources
+
+The ACPI spec defines two methods to describe how a device can wake the system.
+Only one of these methods should be used, otherwise duplicate wake events will
+be generated.
+
+### Using GPEs as a wake source
+
+The `wake` property specified above is used to tell the ACPI subsystem that the
+device can use a GPE to wake the system. The OS can control whether to enable
+or disable the wake source by unmasking/masking off the GPE.
+
+The `GPIO` -> `GPE` mapping must be configured in firmware. On AMD platforms this is
+generally done by a mainboard specific `gpio.c` file that defines the GPIO
+using `PAD_SCI`. The `GPIO` -> `GPE` mapping is returned by the
+`soc_get_gpio_event_table` method that is defined in the SoC specific `gpio.c`
+file. On Intel platforms, you fill in the `pmc_gpe0_dw0`, `pmc_gpe0_dw1`, and
+`pmc_gpe0_dw2` fields in the devicetree to map 3 GPIO communities to `tier-1`
+GPEs (the rest are available as `tier-2` GPEs).
+
+Windows has a large caveat when using this method. If you use the `gpio_irq`
+property to define a `GpioInt` in the `_CRS`, and then use the `wake` property
+to define a `GPE`, Windows will
+[BSOD](https://github.com/MicrosoftDocs/windows-driver-docs/blob/staging/windows-driver-docs-pr/debugger/bug-check-0xa5--acpi-bios-error.md)
+complaining about an invalid ACPI configuration.
+> 0x1000D - A device used both GPE and GPIO interrupts, which is not supported.
+
+In order to avoid this error, you should use the `irq` property instead. AMD
+platforms don't support routing GPIOs to the IO-APIC, so this workaround isn't
+feasible. The other option is to use a wake capable GPIO as described below.
+
+### Using GPIO interrupts as a wake source
+
+The `ACPI_IRQ_WAKE_{EDGE,LEVEL}_{LOW,HIGH}` macros can be used when setting the
+`irq` or `gpio_irq` properties. This ends up setting `ExclusiveAndWake` or
+`SharedAndWake` on the `Interrupt` or `GpioInt` ACPI resource.
+
+This method has a few caveats:
+* On Intel and AMD platforms the IO-APIC can't wake the system. This means using
+  the `ACPI_IRQ_WAKE_*` macros with the `irq` property won't actually wake the
+  system. Instead you need to use the `gpio_irq` property, or a `GPE` as
+  described above.
+* The OS needs to know how to enable the `wake` bit on the GPIO. For linux this
+  means the platform specific GPIO controller driver must implement the
+  `irq_set_wake` callback. For AMD systems this wasn't
+  [implemented](https://github.com/torvalds/linux/commit/d62bd5ce12d79bcd6a6c3e4381daa7375dc21158)
+  until linux v5.15. If the controller doesn't define this callback, it's
+  possible for the firmware to manually set the `wake` bit on the GPIO. This is
+  often done in a mainboard-specific file named `gpio.c`. This is not
+  recommended because then it's not possible for the OS to disable the wake
+  source.
+* As of
+  [linux v6.0-rc5](https://github.com/torvalds/linux/releases/tag/v6.0-rc5),
+  the ACPI subsystem doesn't take the interrupt `wake` bit into account when
+  deciding on which power state to put the device in before suspending the
+  system. This means that if you define a power resource for a device via
+  `has_power_resource`, `enable_gpio`, etc, then the linux kernel will place the
+  device into D3Cold. i.e., power off the device.
+
 ## Other auto-generated names
 
 (see [ACPI specification
@@ -200,17 +268,19 @@ found on.  In this example, this is I2C bus 0.  This also determines the ACPI
 for more details on ACPI methods)
 
 ### _S0W (S0 Device Wake State)
-_S0W indicates the deepest S0 sleep state this device can wake itself from,
-which in this case is ACPI_DEVICE_SLEEP_D3_HOT, representing _D3hot_.
+\_S0W indicates the deepest S0 sleep state this device can wake itself from,
+which in this case is `ACPI_DEVICE_SLEEP_D3_HOT`, representing _D3hot_.
+D3Hot means the `PR3` power resources are still on and the device is still
+responsive on the bus. For i2c devices this is generally the same state as `D0`.
 
-### _PRW (Power Resources for Wake)
-_PRW indicates the power resources and events required for wake.  There are no
+### \_PRW (Power Resources for Wake)
+\_PRW indicates the power resources and events required for wake.  There are no
 dependent power resources, but the GPE (GPE0_DW0_21) is mentioned here (0x15),
 as well as the deepest sleep state supporting waking the system (3), which is
 S3.
 
-### _STA (Status)
-The _STA method is generated automatically, and its values, 0xF, indicates the
+### \_STA (Status)
+The \_STA method is generated automatically, and its values, 0xF, indicates the
 following:
 
     Bit [0] – Set if the device is present.
@@ -218,8 +288,8 @@ following:
     Bit [2] – Set if the device should be shown in the UI.
     Bit [3] – Set if the device is functioning properly (cleared if device failed its diagnostics).
 
-### _CRS (Current resource settings)
-The _CRS method is generated automatically, as the driver knows it is an I2C
+### \_CRS (Current resource settings)
+The \_CRS method is generated automatically, as the driver knows it is an I2C
 controller, and so specifies how to configure the controller for proper
 operation with the touchpad.