Re: [PATCH v4 03/12] i3c: master: Support ACPI enumeration of child devices

On Tue, Jun 16, 2026 at 09:54:17AM +0000, Akhil R wrote:
> Although the existing subsystem allows host controllers to register
> through the ACPI table, it was not possible to describe I3C or I2C
> devices when using ACPI. This is because the driver relied on the reg
> property to retrieve the PID, static address, etc., whereas ACPI uses
> _ADR or serial resources to describe such devices.
>
> Read _ADR and LVR from ACPI resources and extract the data as per the
> ACPI specification for an I3C bus. Also read mipi-i3c-static-address as
> per the MIPI DISCO specifications [1] to get the static address to be
> used.
>
> Enable describing I3C or I2C devices in the ACPI table. This is required
> if the device uses a static address or if it needs device-specific
> properties.
>
> [1] https://www.mipi.org/mipi-disco-for-i3c-download
>
> Signed-off-by: Akhil R <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

>  drivers/i3c/master.c | 149 ++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 141 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index 3b19a5e8f46d..f0e05bcac26d 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -5,6 +5,7 @@
>   * Author: Boris Brezillon <[email protected]>
>   */
>
> +#include <linux/acpi.h>
>  #include <linux/atomic.h>
>  #include <linux/bitmap.h>
>  #include <linux/bug.h>
> @@ -2596,6 +2597,55 @@ EXPORT_SYMBOL_GPL(i3c_master_do_daa);
>
>  #define OF_I3C_REG1_IS_I2C_DEV			BIT(31)
>
> +#ifdef CONFIG_ACPI
> +static int i3c_acpi_get_i2c_resource(struct acpi_resource *ares, void *data)
> +{
> +	struct i2c_dev_boardinfo *boardinfo = data;
> +	struct acpi_resource_i2c_serialbus *sb;
> +
> +	if (boardinfo->base.addr || !i2c_acpi_get_i2c_resource(ares, &sb))
> +		return 1;
> +
> +	boardinfo->base.addr = sb->slave_address;
> +	if (sb->access_mode == ACPI_I2C_10BIT_MODE)
> +		boardinfo->base.flags |= I2C_CLIENT_TEN;
> +
> +	boardinfo->lvr = sb->lvr;
> +
> +	return 1;
> +}
> +
> +static int i3c_acpi_add_i2c_boardinfo(struct i2c_dev_boardinfo *boardinfo,
> +				      struct fwnode_handle *fwnode)
> +{
> +	struct acpi_device *adev = to_acpi_device_node(fwnode);
> +	LIST_HEAD(resources);
> +	int ret;
> +
> +	boardinfo->base.fwnode = acpi_fwnode_handle(adev);
> +	acpi_set_modalias(adev, dev_name(&adev->dev), boardinfo->base.type,
> +			  sizeof(boardinfo->base.type));
> +
> +	ret = acpi_dev_get_resources(adev, &resources,
> +				     i3c_acpi_get_i2c_resource, boardinfo);
> +	if (ret < 0)
> +		return ret;
> +
> +	acpi_dev_free_resource_list(&resources);
> +
> +	if (!boardinfo->base.addr)
> +		return -ENODEV;
> +
> +	return 0;
> +}
> +#else
> +static inline int i3c_acpi_add_i2c_boardinfo(struct i2c_dev_boardinfo *boardinfo,
> +					     struct fwnode_handle *fwnode)
> +{
> +	return -ENODEV;
> +}
> +#endif
> +
>  static int
>  i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
>  			     struct fwnode_handle *fwnode, u32 *reg)
> @@ -2612,6 +2662,13 @@ i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
>  		ret = of_i2c_get_board_info(dev, to_of_node(fwnode), &boardinfo->base);
>  		if (ret)
>  			return ret;
> +
> +		/* LVR is encoded in reg[2] for Device Tree. */
> +		boardinfo->lvr = reg[2];
> +	} else if (is_acpi_device_node(fwnode)) {
> +		ret = i3c_acpi_add_i2c_boardinfo(boardinfo, fwnode);
> +		if (ret)
> +			return ret;
>  	} else {
>  		return -EINVAL;
>  	}
> @@ -2626,9 +2683,6 @@ i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
>  		return -EOPNOTSUPP;
>  	}
>
> -	/* LVR is encoded in reg[2]. */
> -	boardinfo->lvr = reg[2];
> -
>  	list_add_tail(&boardinfo->node, &master->boardinfo.i2c);
>  	fwnode_handle_get(fwnode);
>
> @@ -2683,8 +2737,8 @@ i3c_master_add_i3c_boardinfo(struct i3c_master_controller *master,
>  	return 0;
>  }
>
> -static int i3c_master_add_dev(struct i3c_master_controller *master,
> -			      struct fwnode_handle *fwnode)
> +static int i3c_master_add_of_dev(struct i3c_master_controller *master,
> +				 struct fwnode_handle *fwnode)
>  {
>  	u32 reg[3];
>  	int ret;
> @@ -2708,6 +2762,74 @@ static int i3c_master_add_dev(struct i3c_master_controller *master,
>  	return ret;
>  }
>
> +#ifdef CONFIG_ACPI
> +static int i3c_master_add_acpi_dev(struct i3c_master_controller *master,
> +				   struct fwnode_handle *fwnode)
> +{
> +	struct acpi_device *adev = to_acpi_device_node(fwnode);
> +	acpi_bus_address adr;
> +	u32 reg[3] = { 0 };
> +	int ret;
> +
> +	/*
> +	 * If the ACPI table entry has _ADR method, it's an I3C device.
> +	 * Otherwise it may be an I2C device described by an I2cSerialBus
> +	 * resource. If no I2cSerialBus resource is found, ignore the entry.
> +	 */
> +	if (!acpi_has_method(adev->handle, "_ADR")) {
> +		ret = i3c_master_add_i2c_boardinfo(master, fwnode, reg);
> +		if (ret == -ENODEV)
> +			return 0;
> +
> +		return ret;
> +	}
> +
> +	adr = acpi_device_adr(adev);
> +
> +	/* For I3C devices, _ADR will have the 48 bit PID of the device  */
> +	reg[1] = upper_32_bits(adr);
> +	reg[2] = lower_32_bits(adr);
> +
> +	fwnode_property_read_u32(fwnode, "mipi-i3c-static-address", &reg[0]);
> +
> +	return i3c_master_add_i3c_boardinfo(master, fwnode, reg);
> +}
> +
> +static u8 i3c_acpi_i2c_get_lvr(struct i2c_client *client)
> +{
> +	struct acpi_device *adev = to_acpi_device_node(client->dev.fwnode);
> +	struct i2c_dev_boardinfo boardinfo = {};
> +	LIST_HEAD(resources);
> +	int ret;
> +	u8 lvr;
> +
> +	lvr = I3C_LVR_I2C_INDEX(2) | I3C_LVR_I2C_FM_MODE;
> +
> +	ret = acpi_dev_get_resources(adev, &resources,
> +				     i3c_acpi_get_i2c_resource, &boardinfo);
> +	if (ret < 0)
> +		return lvr;
> +
> +	if (boardinfo.base.addr)
> +		lvr = boardinfo.lvr;
> +
> +	acpi_dev_free_resource_list(&resources);
> +
> +	return lvr;
> +}
> +#else
> +static inline int i3c_master_add_acpi_dev(struct i3c_master_controller *master,
> +					  struct fwnode_handle *fwnode)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline u8 i3c_acpi_i2c_get_lvr(struct i2c_client *client)
> +{
> +	return I3C_LVR_I2C_INDEX(2) | I3C_LVR_I2C_FM_MODE;
> +}
> +#endif
> +
>  static int fwnode_populate_i3c_bus(struct i3c_master_controller *master)
>  {
>  	struct device *dev = &master->dev;
> @@ -2719,7 +2841,13 @@ static int fwnode_populate_i3c_bus(struct i3c_master_controller *master)
>  		return 0;
>
>  	fwnode_for_each_available_child_node_scoped(fwnode, child) {
> -		ret = i3c_master_add_dev(master, child);
> +		if (is_of_node(child))
> +			ret = i3c_master_add_of_dev(master, child);
> +		else if (is_acpi_device_node(child))
> +			ret = i3c_master_add_acpi_dev(master, child);
> +		else
> +			continue;
> +
>  		if (ret)
>  			return ret;
>  	}
> @@ -2787,8 +2915,13 @@ static u8 i3c_master_i2c_get_lvr(struct i2c_client *client)
>  	u8 lvr = I3C_LVR_I2C_INDEX(2) | I3C_LVR_I2C_FM_MODE;
>  	u32 reg[3];
>
> -	if (!fwnode_property_read_u32_array(client->dev.fwnode, "reg", reg, ARRAY_SIZE(reg)))
> -		lvr = reg[2];
> +	if (is_of_node(client->dev.fwnode)) {
> +		if (!fwnode_property_read_u32_array(client->dev.fwnode, "reg",
> +						    reg, ARRAY_SIZE(reg)))
> +			lvr = reg[2];
> +	} else if (is_acpi_device_node(client->dev.fwnode)) {
> +		lvr = i3c_acpi_i2c_get_lvr(client);
> +	}
>
>  	return lvr;
>  }
> --
> 2.43.0
>

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