acpi_device: Add support for writing ACPI I2C descriptors

Add required definitions to describe an ACPI I2C bus and a method to
write the I2cSerialBus() descriptor to the SSDT.

This will be used by device drivers to describe their I2C resources to
the OS.  The devicetree i2c device can supply the address and 7 or 10
bit mode as well as indicate the GPIO controller device, and the bus
speed can be fixed or configured by the driver.

chip.h:
  struct drivers_i2c_generic_config {
    enum i2c_speed bus_speed;
  };

generic.c:
  void acpi_fill_ssdt_generator(struct device *dev) {
    struct drivers_i2c_generic_config *config = dev->chip_info;
    struct acpi_i2c i2c = {
      .address = dev->path->i2c.device,
      .mode_10bit = dev->path.i2c.mode_10bit,
      .speed = config->bus_speed ? : I2C_SPEED_FAST,
      .resource = acpi_device_path(dev->bus->dev)
    };
    ...
    acpi_device_write_i2c(&i2c);
    ...
  }

devicetree.cb:
  device pci 15.0 on
    chip drivers/i2c/generic
      device i2c 10.0 on end
    end
  end

SSDT.dsl:
  I2cSerialBus (0x10, ControllerInitiated, 400000, AddressingMode7Bit,
                "\\_SB.PCI0.I2C0", 0, ResourceConsumer)

Change-Id: I598401ac81a92c72f19da0271af1e218580a6c49
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/14935
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

3 files changed, 98 insertions, 0 deletions

diff --git a/src/arch/x86/acpi_device.c b/src/arch/x86/acpi_device.c
index 610b922b34..3c0230fae2 100644
--- a/src/arch/x86/acpi_device.c
+++ b/src/arch/x86/acpi_device.c
@@ -18,6 +18,7 @@
 #include <arch/acpi_device.h>
 #include <arch/acpigen.h>
 #include <device/device.h>
+#include <device/i2c.h>
 #include <device/path.h>
 #if IS_ENABLED(CONFIG_GENERIC_GPIO_LIB)
 #include <gpio.h>
@@ -323,3 +324,60 @@ void acpi_device_write_gpio(const struct acpi_gpio *gpio)
 	/* Fill in GPIO Descriptor Length (account for len word) */
 	acpi_device_fill_len(desc_length);
 }
+
+/* ACPI 6.1 section 6.4.3.8.2.1 - I2cSerialBus() */
+void acpi_device_write_i2c(const struct acpi_i2c *i2c)
+{
+	void *desc_length, *type_length;
+
+	/* Byte 0: Descriptor Type */
+	acpigen_emit_byte(ACPI_DESCRIPTOR_SERIAL_BUS);
+
+	/* Byte 1+2: Length (filled in later) */
+	desc_length = acpi_device_write_zero_len();
+
+	/* Byte 3: Revision ID */
+	acpigen_emit_byte(ACPI_SERIAL_BUS_REVISION_ID);
+
+	/* Byte 4: Resource Source Index is Reserved */
+	acpigen_emit_byte(0);
+
+	/* Byte 5: Serial Bus Type is I2C */
+	acpigen_emit_byte(ACPI_SERIAL_BUS_TYPE_I2C);
+
+	/*
+	 * Byte 6: Flags
+	 *  [7:2]: 0 => Reserved
+	 *    [1]: 1 => ResourceConsumer
+	 *    [0]: 0 => ControllerInitiated
+	 */
+	acpigen_emit_byte(1 << 1);
+
+	/*
+	 * Byte 7-8: Type Specific Flags
+	 *   [15:1]: 0 => Reserved
+	 *      [0]: 0 => 7bit, 1 => 10bit
+	 */
+	acpigen_emit_word(i2c->mode_10bit);
+
+	/* Byte 9: Type Specific Revision ID */
+	acpigen_emit_byte(ACPI_SERIAL_BUS_REVISION_ID);
+
+	/* Byte 10-11: I2C Type Data Length */
+	type_length = acpi_device_write_zero_len();
+
+	/* Byte 12-15: I2C Bus Speed */
+	acpigen_emit_dword(i2c->speed);
+
+	/* Byte 16-17: I2C Slave Address */
+	acpigen_emit_word(i2c->address);
+
+	/* Fill in Type Data Length */
+	acpi_device_fill_len(type_length);
+
+	/* Byte 18+: ResourceSource */
+	acpigen_emit_string(i2c->resource);
+
+	/* Fill in I2C Descriptor Length */
+	acpi_device_fill_len(desc_length);
+}
diff --git a/src/arch/x86/include/arch/acpi_device.h b/src/arch/x86/include/arch/acpi_device.h
index a81cee0087..7b5001f65a 100644
--- a/src/arch/x86/include/arch/acpi_device.h
+++ b/src/arch/x86/include/arch/acpi_device.h
@@ -16,11 +16,13 @@
 #ifndef __ACPI_DEVICE_H
 #define __ACPI_DEVICE_H
 
+#include <device/i2c.h>
 #include <stdint.h>
 
 #define ACPI_DESCRIPTOR_LARGE		(1 << 7)
 #define ACPI_DESCRIPTOR_INTERRUPT	(ACPI_DESCRIPTOR_LARGE | 9)
 #define ACPI_DESCRIPTOR_GPIO		(ACPI_DESCRIPTOR_LARGE | 12)
+#define ACPI_DESCRIPTOR_SERIAL_BUS	(ACPI_DESCRIPTOR_LARGE | 14)
 
 struct device;
 const char *acpi_device_name(struct device *dev);
@@ -157,4 +159,29 @@ struct acpi_gpio {
 /* Write GpioIo() or GpioInt() descriptor to SSDT AML output */
 void acpi_device_write_gpio(const struct acpi_gpio *gpio);
 
+/*
+ * ACPI Descriptors for Serial Bus interfaces
+ */
+
+#define ACPI_SERIAL_BUS_TYPE_I2C	1
+#define ACPI_SERIAL_BUS_REVISION_ID	1
+
+/*
+ * ACPI I2C Bus
+ */
+
+struct acpi_i2c {
+	/* I2C Address */
+	uint16_t address;
+	/* 7 or 10 bit Address Mode */
+	enum i2c_address_mode mode_10bit;
+	/* I2C Bus Speed in Hz */
+	enum i2c_speed speed;
+	/* Reference to I2C controller */
+	const char *resource;
+};
+
+/* Write I2cSerialBus() descriptor to SSDT AML output */
+void acpi_device_write_i2c(const struct acpi_i2c *i2c);
+
 #endif
diff --git a/src/include/device/i2c.h b/src/include/device/i2c.h
index b152bb98c2..c8c7b2283d 100644
--- a/src/include/device/i2c.h
+++ b/src/include/device/i2c.h
@@ -19,6 +19,19 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+enum i2c_speed {
+	I2C_SPEED_STANDARD	= 100000,
+	I2C_SPEED_FAST		= 400000,
+	I2C_SPEED_FAST_PLUS	= 1000000,
+	I2C_SPEED_HIGH		= 3400000,
+	I2C_SPEED_FAST_ULTRA	= 5000000,
+};
+
+enum i2c_address_mode {
+	I2C_MODE_7_BIT,
+	I2C_MODE_10_BIT
+};
+
 struct i2c_seg
 {
 	int read;