Re: [PATCH iwl-next v5] igc: Support ACPI-based MAC passthrough

["Chia-Lin Kao (AceLan)" <acelan.kao@canonical.com>]

On Mon, Oct 12, 2026 at 10:48:17PM +0300, Dima Ruinskiy wrote:
> Some systems implement a system MAC address object in the ACPI table,
> using either \\_SB.AMAC or \\MACA object names. This system MAC address,
> when enabled, is intended to override the permanent MAC address of the
> any network controller attached via a docking station. The purpose is to
> allow the host PC retain its network identity in a corporate environment,
> regardless of the specific docking station it is connected to. The
> expectation is that only one docking station is attached at a time, or
> that only a single network controller is plugged in at a time.
>
> Implement seamless passthrough of the system MAC address to the
> I225/I226 network controller, by looking up the relevant ACPI object names
> and using them to initialize the MAC address. Limit the lookup only to
> controllers that are Thunderbolt-attached, as these are the only docking
> stations that can pass through an I225/I226 controller to the host.
>
> On systems where the feature is disabled or unsupported, the ACPI objects
> do not exist or do not contain a valid Ethernet MAC, the default MAC
> address of the device is used.
>
> Assisted-by: GitHub-Copilot:claude-opus-4.7
> Signed-off-by: Dima Ruinskiy <dima.ruinskiy@intel.com>
This patch fix the dock's ethernet hotplug connectivity issue,
please consider to merge it, thanks.

Tested-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>

> ---
> Change log
> v4->v5:
> 	align MAC address to 2 bytes (required by helper functions)
> v3->v4:
> 	use pci_is_thunderbolt_attached instead of device id check
> 	explicitly save permanent address when using passthrough mac
> v2->v3:
> 	fix typo that introduced check reversal
> v1->v2:
> 	limit scope to dock device ids
> ---
>  drivers/net/ethernet/intel/igc/igc_main.c | 70 +++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index f6d1ee75627d..d51e9bcdfc3e 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -1,6 +1,8 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /* Copyright (c)  2018 Intel Corporation */
>
> +#include <linux/acpi.h>
> +#include <linux/hex.h>
>  #include <linux/module.h>
>  #include <linux/types.h>
>  #include <linux/if_vlan.h>
> @@ -7134,6 +7136,58 @@ static enum hrtimer_restart igc_qbv_scheduling_timer(struct hrtimer *timer)
>  	return HRTIMER_NORESTART;
>  }
>
> +static bool igc_get_acpi_mac_passthru(u8 *mac)
> +{
> +	static const struct {
> +		const char *name;
> +		acpi_object_type type;
> +		u32 length;
> +	} sources[] = {
> +		{ "\\_SB.AMAC", ACPI_TYPE_BUFFER, 23 },
> +		{ "\\MACA",     ACPI_TYPE_STRING, 22 },
> +	};
> +	struct acpi_buffer buffer;
> +	union acpi_object *obj;
> +	bool mac_found = false;
> +	acpi_status status;
> +	u8 buf[ETH_ALEN] __aligned(2);
> +	int i;
> +
> +	if (!IS_ENABLED(CONFIG_ACPI))
> +		return false;
> +
> +	for (i = 0; i < ARRAY_SIZE(sources) && !mac_found; i++) {
> +		buffer.length = ACPI_ALLOCATE_BUFFER;
> +		buffer.pointer = NULL;
> +
> +		status = acpi_evaluate_object(NULL, (char *)sources[i].name,
> +					      NULL, &buffer);
> +		if (ACPI_FAILURE(status))
> +			continue;
> +
> +		obj = buffer.pointer;
> +		if (!obj || obj->type != sources[i].type ||
> +		    obj->string.length != sources[i].length ||
> +		    !obj->string.pointer)
> +			goto free_obj;
> +
> +		if (strncmp(obj->string.pointer, "_AUXMAC_#", 9) ||
> +		    obj->string.pointer[21] != '#')
> +			goto free_obj;
> +
> +		if (hex2bin(buf, obj->string.pointer + 9, ETH_ALEN) ||
> +		    !is_valid_ether_addr(buf))
> +			goto free_obj;
> +
> +		ether_addr_copy(mac, buf);
> +		mac_found = true;
> +free_obj:
> +		ACPI_FREE(obj);
> +	}
> +
> +	return mac_found;
> +}
> +
>  /**
>   * igc_probe - Device Initialization Routine
>   * @pdev: PCI device information struct
> @@ -7300,6 +7354,22 @@ static int igc_probe(struct pci_dev *pdev,
>  		/* copy the MAC address out of the NVM */
>  		if (hw->mac.ops.read_mac_addr(hw))
>  			dev_err(&pdev->dev, "NVM Read Error\n");
> +
> +		/* For devices behind a Thunderbolt/USB4 dock, look for a
> +		 * system-provided MAC in the ACPI table
> +		 */
> +		if (pci_is_thunderbolt_attached(pdev) &&
> +		    igc_get_acpi_mac_passthru(hw->mac.addr)) {
> +			/* Set the permanent MAC address. Leave blank if invalid to
> +			 * reflect there is something wrong with the NVM MAC.
> +			 */
> +			if (is_valid_ether_addr(hw->mac.perm_addr))
> +				ether_addr_copy(netdev->perm_addr, hw->mac.perm_addr);
> +			netdev->addr_assign_type = NET_ADDR_STOLEN;
> +			dev_info(&pdev->dev,
> +				 "Using ACPI pass-thru MAC addr %pM\n",
> +				 hw->mac.addr);
> +		}
>  	}
>
>  	eth_hw_addr_set(netdev, hw->mac.addr);