[v2,11/35] acpi: Support generation of I2C descriptor

Message ID 20200510203409.203520-9-sjg@chromium.org
State New
Headers show
Series
  • dm: Add programmatic generation of ACPI tables (part B)
Related show

Commit Message

Simon Glass May 10, 2020, 8:33 p.m.
Add a function to write a GPIO descriptor to the generated ACPI code.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

Changes in v2:
- Fix memset of I2C descriptor

Changes in v1: None

 drivers/i2c/sandbox_i2c.c  |  11 ++++
 drivers/rtc/sandbox_rtc.c  |  13 +++++
 include/acpi/acpi_device.h |  36 +++++++++++++
 lib/acpi/acpi_device.c     | 103 +++++++++++++++++++++++++++++++++++++
 test/dm/acpigen.c          |  32 ++++++++++++
 5 files changed, 195 insertions(+)

Comments

Wolfgang Wallner May 19, 2020, 11:58 a.m. | #1
Hi Simon,

-----"Simon Glass" <sjg at chromium.org> schrieb: -----
> Betreff: [PATCH v2 11/35] acpi: Support generation of I2C descriptor
> 
> Add a function to write a GPIO descriptor to the generated ACPI code.
> 
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
> 
> Changes in v2:
> - Fix memset of I2C descriptor
> 
> Changes in v1: None
> 
>  drivers/i2c/sandbox_i2c.c  |  11 ++++
>  drivers/rtc/sandbox_rtc.c  |  13 +++++
>  include/acpi/acpi_device.h |  36 +++++++++++++
>  lib/acpi/acpi_device.c     | 103 +++++++++++++++++++++++++++++++++++++
>  test/dm/acpigen.c          |  32 ++++++++++++
>  5 files changed, 195 insertions(+)
> 
> diff --git a/drivers/i2c/sandbox_i2c.c b/drivers/i2c/sandbox_i2c.c
> index f4ae2397a0..125026da90 100644
> --- a/drivers/i2c/sandbox_i2c.c
> +++ b/drivers/i2c/sandbox_i2c.c
> @@ -11,6 +11,7 @@
>  #include <i2c.h>
>  #include <log.h>
>  #include <asm/test.h>
> +#include <dm/acpi.h>
>  #include <dm/lists.h>
>  #include <dm/device-internal.h>
>  
> @@ -83,6 +84,15 @@ static int sandbox_i2c_xfer(struct udevice *bus, struct i2c_msg *msg,
>  	return ops->xfer(emul, msg, nmsgs);
>  }
>  
> +static int sandbox_i2c_get_name(const struct udevice *dev, char *out_name)
> +{
> +	return acpi_copy_name(out_name, "SI2C");
> +}
> +
> +struct acpi_ops sandbox_i2c_acpi_ops = {
> +	.get_name	= sandbox_i2c_get_name,
> +};
> +
>  static const struct dm_i2c_ops sandbox_i2c_ops = {
>  	.xfer		= sandbox_i2c_xfer,
>  };
> @@ -98,4 +108,5 @@ U_BOOT_DRIVER(i2c_sandbox) = {
>  	.of_match = sandbox_i2c_ids,
>  	.ops	= &sandbox_i2c_ops,
>  	.priv_auto_alloc_size = sizeof(struct sandbox_i2c_priv),
> +	ACPI_OPS_PTR(&sandbox_i2c_acpi_ops)
>  };
> diff --git a/drivers/rtc/sandbox_rtc.c b/drivers/rtc/sandbox_rtc.c
> index b08d758a74..f2906c3397 100644
> --- a/drivers/rtc/sandbox_rtc.c
> +++ b/drivers/rtc/sandbox_rtc.c
> @@ -9,6 +9,7 @@
>  #include <i2c.h>
>  #include <rtc.h>
>  #include <asm/rtc.h>
> +#include <dm/acpi.h>
>  
>  #define REG_COUNT 0x80
>  
> @@ -84,6 +85,17 @@ static int sandbox_rtc_write8(struct udevice *dev, unsigned int reg, int val)
>  	return dm_i2c_reg_write(dev, reg, val);
>  }
>  
> +#if CONFIG_IS_ENABLED(ACPIGEN)
> +static int sandbox_rtc_get_name(const struct udevice *dev, char *out_name)
> +{
> +	return acpi_copy_name(out_name, "RTCC");
> +}
> +
> +struct acpi_ops sandbox_rtc_acpi_ops = {
> +	.get_name	= sandbox_rtc_get_name,
> +};
> +#endif
> +
>  static const struct rtc_ops sandbox_rtc_ops = {
>  	.get = sandbox_rtc_get,
>  	.set = sandbox_rtc_set,
> @@ -102,4 +114,5 @@ U_BOOT_DRIVER(rtc_sandbox) = {
>  	.id	= UCLASS_RTC,
>  	.of_match = sandbox_rtc_ids,
>  	.ops	= &sandbox_rtc_ops,
> +	ACPI_OPS_PTR(&sandbox_rtc_acpi_ops)
>  };
> diff --git a/include/acpi/acpi_device.h b/include/acpi/acpi_device.h
> index 70c151d150..cf1ac695a7 100644
> --- a/include/acpi/acpi_device.h
> +++ b/include/acpi/acpi_device.h
> @@ -9,6 +9,7 @@
>  #ifndef __ACPI_DEVICE_H
>  #define __ACPI_DEVICE_H
>  
> +#include <i2c.h>
>  #include <linux/bitops.h>
>  
>  struct acpi_ctx;
> @@ -183,6 +184,29 @@ struct acpi_gpio {
>  	enum acpi_gpio_polarity polarity;
>  };
>  
> +/* ACPI Descriptors for Serial Bus interfaces */
> +#define ACPI_SERIAL_BUS_TYPE_I2C		1
> +#define ACPI_SERIAL_BUS_TYPE_SPI		2
> +#define ACPI_I2C_SERIAL_BUS_REVISION_ID		1 /* TODO: upgrade to 2 */
> +#define ACPI_I2C_TYPE_SPECIFIC_REVISION_ID	1
> +#define ACPI_SPI_SERIAL_BUS_REVISION_ID		1
> +#define ACPI_SPI_TYPE_SPECIFIC_REVISION_ID	1
> +
> +/**
> + * struct acpi_i2c - representation of an ACPI I2C device
> + *
> + * @address: 7-bit or 10-bit I2C address
> + * @mode_10bit: Which address size is used
> + * @speed: Bus speed in Hz
> + * @resource: Resource name for the I2C controller
> + */
> +struct acpi_i2c {
> +	u16 address;
> +	enum i2c_address_mode mode_10bit;
> +	enum i2c_speed_rate speed;
> +	const char *resource;
> +};
> +
>  /**
>   * acpi_device_path() - Get the full path to an ACPI device
>   *
> @@ -270,4 +294,16 @@ int acpi_device_write_gpio_desc(struct acpi_ctx *ctx,
>  int acpi_device_write_interrupt_or_gpio(struct acpi_ctx *ctx,
>  					struct udevice *dev, const char *prop);
>  
> +/**
> + * acpi_device_write_i2c_dev() - Write an I2C device to ACPI
> + *
> + * This creates a I2cSerialBus descriptor for an I2C device, including
> + * information ACPI needs to use it.
> + *
> + * @ctx: ACPI context pointer
> + * @dev: I2C device to write
> + * @return 0 if OK, -ve on error
> + */
> +int acpi_device_write_i2c_dev(struct acpi_ctx *ctx, const struct udevice *dev);
> +
>  #endif
> diff --git a/lib/acpi/acpi_device.c b/lib/acpi/acpi_device.c
> index 423b91cfd2..0136a0bdc9 100644
> --- a/lib/acpi/acpi_device.c
> +++ b/lib/acpi/acpi_device.c
> @@ -381,3 +381,106 @@ int acpi_device_write_interrupt_or_gpio(struct acpi_ctx *ctx,
>  
>  	return 0;
>  }
> +
> +/* ACPI 6.3 section 6.4.3.8.2.1 - I2cSerialBus() */
> +static void acpi_device_write_i2c(struct acpi_ctx *ctx,
> +				  const struct acpi_i2c *i2c)
> +{
> +	void *desc_length, *type_length;
> +
> +	/* Byte 0: Descriptor Type */
> +	acpigen_emit_byte(ctx, ACPI_DESCRIPTOR_SERIAL_BUS);
> +
> +	/* Byte 1+2: Length (filled in later) */
> +	desc_length = acpi_device_write_zero_len(ctx);
> +
> +	/* Byte 3: Revision ID */
> +	acpigen_emit_byte(ctx, ACPI_I2C_SERIAL_BUS_REVISION_ID);
> +
> +	/* Byte 4: Resource Source Index is Reserved */
> +	acpigen_emit_byte(ctx, 0);
> +
> +	/* Byte 5: Serial Bus Type is I2C */
> +	acpigen_emit_byte(ctx, ACPI_SERIAL_BUS_TYPE_I2C);
> +
> +	/*
> +	 * Byte 6: Flags
> +	 *  [7:2]: 0 => Reserved
> +	 *    [1]: 1 => ResourceConsumer
> +	 *    [0]: 0 => ControllerInitiated
> +	 */
> +	acpigen_emit_byte(ctx, 1 << 1);
> +
> +	/*
> +	 * Byte 7-8: Type Specific Flags
> +	 *   [15:1]: 0 => Reserved
> +	 *      [0]: 0 => 7bit, 1 => 10bit
> +	 */
> +	acpigen_emit_word(ctx, i2c->mode_10bit);
> +
> +	/* Byte 9: Type Specific Revision ID */
> +	acpigen_emit_byte(ctx, ACPI_I2C_TYPE_SPECIFIC_REVISION_ID);
> +
> +	/* Byte 10-11: I2C Type Data Length */
> +	type_length = acpi_device_write_zero_len(ctx);
> +
> +	/* Byte 12-15: I2C Bus Speed */
> +	acpigen_emit_dword(ctx, i2c->speed);
> +
> +	/* Byte 16-17: I2C Slave Address */
> +	acpigen_emit_word(ctx, i2c->address);
> +
> +	/* Fill in Type Data Length */
> +	acpi_device_fill_len(ctx, type_length);
> +
> +	/* Byte 18+: ResourceSource */
> +	acpigen_emit_string(ctx, i2c->resource);
> +
> +	/* Fill in I2C Descriptor Length */
> +	acpi_device_fill_len(ctx, desc_length);
> +}
> +
> +/**
> + * acpi_device_set_i2c() - Set up an ACPI I2C struct from a device
> + *
> + * @dev: I2C device to convert
> + * @i2c: Place to put the new structure
> + * @scope: Scope of the I2C device (this is the controller path)

>From the declaration I would assume that "scope" is internally copied, but in
the code it is only referenced.
I would propose to add something like the following to its description:
"The value of scope is not copied, but only referenced. This implies the
caller has to ensure it stays valid for the lifetime of i2c."

> + * @return 0 (always)

dev_get_parent_platdata() could return NULL. Should we check this and return
and error?

> + */
> +static int acpi_device_set_i2c(const struct udevice *dev, struct acpi_i2c *i2c,
> +			       const char *scope)
> +{
> +	struct dm_i2c_chip *chip = dev_get_parent_platdata(dev);
> +	struct udevice *bus = dev_get_parent(dev);
> +
> +	memset(i2c, '\0', sizeof(*i2c));

Nit: memset(i2c, 0, sizeof(*i2c));

This is only a style question. But it seems 0 is used for memset in existing
U-Boot code much more often then '\0' (~120 grep results vs ~1100 grep results).

> +	i2c->address = chip->chip_addr;
> +	i2c->mode_10bit = 0;
> +
> +	/*
> +	 * i2c_bus->speed_hz is set if this device is probed, but if not we
> +	 * must use the device tree
> +	 */
> +	i2c->speed = dev_read_u32_default(bus, "clock-frequency", 100000);

Nit: I2C_SPEED_STANDARD_RATE instead of 100000?

> +	i2c->resource = scope;
> +
> +	return 0;
> +}
> +
> +int acpi_device_write_i2c_dev(struct acpi_ctx *ctx, const struct udevice *dev)
> +{
> +	char scope[ACPI_PATH_MAX];
> +	struct acpi_i2c i2c;
> +	int ret;
> +
> +	ret = acpi_device_scope(dev, scope, sizeof(scope));
> +	if (ret)
> +		return log_msg_ret("scope", ret);
> +	ret = acpi_device_set_i2c(dev, &i2c, scope);
> +	if (ret)
> +		return log_msg_ret("set", ret);
> +	acpi_device_write_i2c(ctx, &i2c);
> +
> +	return 0;
> +}
> diff --git a/test/dm/acpigen.c b/test/dm/acpigen.c
> index 6aefa6845d..de9996ab35 100644
> --- a/test/dm/acpigen.c
> +++ b/test/dm/acpigen.c
> @@ -266,3 +266,35 @@ static int dm_test_acpi_interrupt_or_gpio(struct unit_test_state *uts)
>  }
>  DM_TEST(dm_test_acpi_interrupt_or_gpio,
>  	DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);
> +
> +/* Test emitting an I2C descriptor */
> +static int dm_test_acpi_i2c(struct unit_test_state *uts)
> +{
> +	struct acpi_ctx *ctx;
> +	struct udevice *dev;
> +	u8 *ptr;
> +
> +	ut_assertok(alloc_context(&ctx));
> +
> +	ptr = acpigen_get_current(ctx);
> +
> +	ut_assertok(uclass_get_device(UCLASS_RTC, 0, &dev));
> +	ut_assertok(acpi_device_write_i2c_dev(ctx, dev));
> +	ut_asserteq(28, acpigen_get_current(ctx) - ptr);
> +	ut_asserteq(ACPI_DESCRIPTOR_SERIAL_BUS, ptr[0]);
> +	ut_asserteq(25, get_unaligned((u16 *)(ptr + 1)));
> +	ut_asserteq(ACPI_I2C_SERIAL_BUS_REVISION_ID, ptr[3]);
> +	ut_asserteq(0, ptr[4]);
> +	ut_asserteq(ACPI_SERIAL_BUS_TYPE_I2C, ptr[5]);
> +	ut_asserteq(0, get_unaligned((u16 *)(ptr + 7)));
> +	ut_asserteq(ACPI_I2C_TYPE_SPECIFIC_REVISION_ID, ptr[9]);
> +	ut_asserteq(6, get_unaligned((u16 *)(ptr + 10)));
> +	ut_asserteq(100000, get_unaligned((u32 *)(ptr + 12)));
> +	ut_asserteq(0x43, get_unaligned((u16 *)(ptr + 16)));
> +	ut_asserteq_str("\\_SB.SI2C", (char *)ptr + 18);
> +
> +	free_context(&ctx);
> +
> +	return 0;
> +}
> +DM_TEST(dm_test_acpi_i2c, DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);
> -- 
> 2.26.2.645.ge9eca65c58-goog

The remarks above are just this: remarks. I would also be fine with merging
the code as it is:

Reviewed-by: Wolfgang Wallner <wolfgang.wallner at br-automation.com>

Patch

diff --git a/drivers/i2c/sandbox_i2c.c b/drivers/i2c/sandbox_i2c.c
index f4ae2397a0..125026da90 100644
--- a/drivers/i2c/sandbox_i2c.c
+++ b/drivers/i2c/sandbox_i2c.c
@@ -11,6 +11,7 @@ 
 #include <i2c.h>
 #include <log.h>
 #include <asm/test.h>
+#include <dm/acpi.h>
 #include <dm/lists.h>
 #include <dm/device-internal.h>
 
@@ -83,6 +84,15 @@  static int sandbox_i2c_xfer(struct udevice *bus, struct i2c_msg *msg,
 	return ops->xfer(emul, msg, nmsgs);
 }
 
+static int sandbox_i2c_get_name(const struct udevice *dev, char *out_name)
+{
+	return acpi_copy_name(out_name, "SI2C");
+}
+
+struct acpi_ops sandbox_i2c_acpi_ops = {
+	.get_name	= sandbox_i2c_get_name,
+};
+
 static const struct dm_i2c_ops sandbox_i2c_ops = {
 	.xfer		= sandbox_i2c_xfer,
 };
@@ -98,4 +108,5 @@  U_BOOT_DRIVER(i2c_sandbox) = {
 	.of_match = sandbox_i2c_ids,
 	.ops	= &sandbox_i2c_ops,
 	.priv_auto_alloc_size = sizeof(struct sandbox_i2c_priv),
+	ACPI_OPS_PTR(&sandbox_i2c_acpi_ops)
 };
diff --git a/drivers/rtc/sandbox_rtc.c b/drivers/rtc/sandbox_rtc.c
index b08d758a74..f2906c3397 100644
--- a/drivers/rtc/sandbox_rtc.c
+++ b/drivers/rtc/sandbox_rtc.c
@@ -9,6 +9,7 @@ 
 #include <i2c.h>
 #include <rtc.h>
 #include <asm/rtc.h>
+#include <dm/acpi.h>
 
 #define REG_COUNT 0x80
 
@@ -84,6 +85,17 @@  static int sandbox_rtc_write8(struct udevice *dev, unsigned int reg, int val)
 	return dm_i2c_reg_write(dev, reg, val);
 }
 
+#if CONFIG_IS_ENABLED(ACPIGEN)
+static int sandbox_rtc_get_name(const struct udevice *dev, char *out_name)
+{
+	return acpi_copy_name(out_name, "RTCC");
+}
+
+struct acpi_ops sandbox_rtc_acpi_ops = {
+	.get_name	= sandbox_rtc_get_name,
+};
+#endif
+
 static const struct rtc_ops sandbox_rtc_ops = {
 	.get = sandbox_rtc_get,
 	.set = sandbox_rtc_set,
@@ -102,4 +114,5 @@  U_BOOT_DRIVER(rtc_sandbox) = {
 	.id	= UCLASS_RTC,
 	.of_match = sandbox_rtc_ids,
 	.ops	= &sandbox_rtc_ops,
+	ACPI_OPS_PTR(&sandbox_rtc_acpi_ops)
 };
diff --git a/include/acpi/acpi_device.h b/include/acpi/acpi_device.h
index 70c151d150..cf1ac695a7 100644
--- a/include/acpi/acpi_device.h
+++ b/include/acpi/acpi_device.h
@@ -9,6 +9,7 @@ 
 #ifndef __ACPI_DEVICE_H
 #define __ACPI_DEVICE_H
 
+#include <i2c.h>
 #include <linux/bitops.h>
 
 struct acpi_ctx;
@@ -183,6 +184,29 @@  struct acpi_gpio {
 	enum acpi_gpio_polarity polarity;
 };
 
+/* ACPI Descriptors for Serial Bus interfaces */
+#define ACPI_SERIAL_BUS_TYPE_I2C		1
+#define ACPI_SERIAL_BUS_TYPE_SPI		2
+#define ACPI_I2C_SERIAL_BUS_REVISION_ID		1 /* TODO: upgrade to 2 */
+#define ACPI_I2C_TYPE_SPECIFIC_REVISION_ID	1
+#define ACPI_SPI_SERIAL_BUS_REVISION_ID		1
+#define ACPI_SPI_TYPE_SPECIFIC_REVISION_ID	1
+
+/**
+ * struct acpi_i2c - representation of an ACPI I2C device
+ *
+ * @address: 7-bit or 10-bit I2C address
+ * @mode_10bit: Which address size is used
+ * @speed: Bus speed in Hz
+ * @resource: Resource name for the I2C controller
+ */
+struct acpi_i2c {
+	u16 address;
+	enum i2c_address_mode mode_10bit;
+	enum i2c_speed_rate speed;
+	const char *resource;
+};
+
 /**
  * acpi_device_path() - Get the full path to an ACPI device
  *
@@ -270,4 +294,16 @@  int acpi_device_write_gpio_desc(struct acpi_ctx *ctx,
 int acpi_device_write_interrupt_or_gpio(struct acpi_ctx *ctx,
 					struct udevice *dev, const char *prop);
 
+/**
+ * acpi_device_write_i2c_dev() - Write an I2C device to ACPI
+ *
+ * This creates a I2cSerialBus descriptor for an I2C device, including
+ * information ACPI needs to use it.
+ *
+ * @ctx: ACPI context pointer
+ * @dev: I2C device to write
+ * @return 0 if OK, -ve on error
+ */
+int acpi_device_write_i2c_dev(struct acpi_ctx *ctx, const struct udevice *dev);
+
 #endif
diff --git a/lib/acpi/acpi_device.c b/lib/acpi/acpi_device.c
index 423b91cfd2..0136a0bdc9 100644
--- a/lib/acpi/acpi_device.c
+++ b/lib/acpi/acpi_device.c
@@ -381,3 +381,106 @@  int acpi_device_write_interrupt_or_gpio(struct acpi_ctx *ctx,
 
 	return 0;
 }
+
+/* ACPI 6.3 section 6.4.3.8.2.1 - I2cSerialBus() */
+static void acpi_device_write_i2c(struct acpi_ctx *ctx,
+				  const struct acpi_i2c *i2c)
+{
+	void *desc_length, *type_length;
+
+	/* Byte 0: Descriptor Type */
+	acpigen_emit_byte(ctx, ACPI_DESCRIPTOR_SERIAL_BUS);
+
+	/* Byte 1+2: Length (filled in later) */
+	desc_length = acpi_device_write_zero_len(ctx);
+
+	/* Byte 3: Revision ID */
+	acpigen_emit_byte(ctx, ACPI_I2C_SERIAL_BUS_REVISION_ID);
+
+	/* Byte 4: Resource Source Index is Reserved */
+	acpigen_emit_byte(ctx, 0);
+
+	/* Byte 5: Serial Bus Type is I2C */
+	acpigen_emit_byte(ctx, ACPI_SERIAL_BUS_TYPE_I2C);
+
+	/*
+	 * Byte 6: Flags
+	 *  [7:2]: 0 => Reserved
+	 *    [1]: 1 => ResourceConsumer
+	 *    [0]: 0 => ControllerInitiated
+	 */
+	acpigen_emit_byte(ctx, 1 << 1);
+
+	/*
+	 * Byte 7-8: Type Specific Flags
+	 *   [15:1]: 0 => Reserved
+	 *      [0]: 0 => 7bit, 1 => 10bit
+	 */
+	acpigen_emit_word(ctx, i2c->mode_10bit);
+
+	/* Byte 9: Type Specific Revision ID */
+	acpigen_emit_byte(ctx, ACPI_I2C_TYPE_SPECIFIC_REVISION_ID);
+
+	/* Byte 10-11: I2C Type Data Length */
+	type_length = acpi_device_write_zero_len(ctx);
+
+	/* Byte 12-15: I2C Bus Speed */
+	acpigen_emit_dword(ctx, i2c->speed);
+
+	/* Byte 16-17: I2C Slave Address */
+	acpigen_emit_word(ctx, i2c->address);
+
+	/* Fill in Type Data Length */
+	acpi_device_fill_len(ctx, type_length);
+
+	/* Byte 18+: ResourceSource */
+	acpigen_emit_string(ctx, i2c->resource);
+
+	/* Fill in I2C Descriptor Length */
+	acpi_device_fill_len(ctx, desc_length);
+}
+
+/**
+ * acpi_device_set_i2c() - Set up an ACPI I2C struct from a device
+ *
+ * @dev: I2C device to convert
+ * @i2c: Place to put the new structure
+ * @scope: Scope of the I2C device (this is the controller path)
+ * @return 0 (always)
+ */
+static int acpi_device_set_i2c(const struct udevice *dev, struct acpi_i2c *i2c,
+			       const char *scope)
+{
+	struct dm_i2c_chip *chip = dev_get_parent_platdata(dev);
+	struct udevice *bus = dev_get_parent(dev);
+
+	memset(i2c, '\0', sizeof(*i2c));
+	i2c->address = chip->chip_addr;
+	i2c->mode_10bit = 0;
+
+	/*
+	 * i2c_bus->speed_hz is set if this device is probed, but if not we
+	 * must use the device tree
+	 */
+	i2c->speed = dev_read_u32_default(bus, "clock-frequency", 100000);
+	i2c->resource = scope;
+
+	return 0;
+}
+
+int acpi_device_write_i2c_dev(struct acpi_ctx *ctx, const struct udevice *dev)
+{
+	char scope[ACPI_PATH_MAX];
+	struct acpi_i2c i2c;
+	int ret;
+
+	ret = acpi_device_scope(dev, scope, sizeof(scope));
+	if (ret)
+		return log_msg_ret("scope", ret);
+	ret = acpi_device_set_i2c(dev, &i2c, scope);
+	if (ret)
+		return log_msg_ret("set", ret);
+	acpi_device_write_i2c(ctx, &i2c);
+
+	return 0;
+}
diff --git a/test/dm/acpigen.c b/test/dm/acpigen.c
index 6aefa6845d..de9996ab35 100644
--- a/test/dm/acpigen.c
+++ b/test/dm/acpigen.c
@@ -266,3 +266,35 @@  static int dm_test_acpi_interrupt_or_gpio(struct unit_test_state *uts)
 }
 DM_TEST(dm_test_acpi_interrupt_or_gpio,
 	DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);
+
+/* Test emitting an I2C descriptor */
+static int dm_test_acpi_i2c(struct unit_test_state *uts)
+{
+	struct acpi_ctx *ctx;
+	struct udevice *dev;
+	u8 *ptr;
+
+	ut_assertok(alloc_context(&ctx));
+
+	ptr = acpigen_get_current(ctx);
+
+	ut_assertok(uclass_get_device(UCLASS_RTC, 0, &dev));
+	ut_assertok(acpi_device_write_i2c_dev(ctx, dev));
+	ut_asserteq(28, acpigen_get_current(ctx) - ptr);
+	ut_asserteq(ACPI_DESCRIPTOR_SERIAL_BUS, ptr[0]);
+	ut_asserteq(25, get_unaligned((u16 *)(ptr + 1)));
+	ut_asserteq(ACPI_I2C_SERIAL_BUS_REVISION_ID, ptr[3]);
+	ut_asserteq(0, ptr[4]);
+	ut_asserteq(ACPI_SERIAL_BUS_TYPE_I2C, ptr[5]);
+	ut_asserteq(0, get_unaligned((u16 *)(ptr + 7)));
+	ut_asserteq(ACPI_I2C_TYPE_SPECIFIC_REVISION_ID, ptr[9]);
+	ut_asserteq(6, get_unaligned((u16 *)(ptr + 10)));
+	ut_asserteq(100000, get_unaligned((u32 *)(ptr + 12)));
+	ut_asserteq(0x43, get_unaligned((u16 *)(ptr + 16)));
+	ut_asserteq_str("\\_SB.SI2C", (char *)ptr + 18);
+
+	free_context(&ctx);
+
+	return 0;
+}
+DM_TEST(dm_test_acpi_i2c, DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);