[PATCH v2 1/2] usb: xhci-pci: add generic auxiliary device interface

[Jihong Min <hurryman2212@gmail.com>]

Some xHCI PCI controllers expose controller-specific functionality that is
not part of generic xHCI operation and is better handled by optional child
drivers in other subsystems. Add a small auxiliary device registration path
for selected xHCI PCI controllers.

The initial table creates an xhci_pci.hwmon auxiliary device for AMD
1022:43fd controllers. Store the created auxiliary device in devres so the
xhci-pci remove path destroys it before HCD teardown. Use a
PCI-domain-qualified id so auxiliary device names remain unique across PCI
domains.

This keeps xhci-pci responsible only for publishing selected controller
functions while allowing subsystem-specific drivers to bind through the
auxiliary bus.

Assisted-by: Codex:gpt-5.5
Signed-off-by: Jihong Min <hurryman2212@gmail.com>
---
 drivers/usb/host/Kconfig    |  10 ++++
 drivers/usb/host/xhci-pci.c | 114 ++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+)

diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index 0a277a07cf70..e0c2c7ac5c97 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig
@@ -42,6 +42,16 @@ config USB_XHCI_PCI
 	depends on USB_PCI
 	default y
 
+config USB_XHCI_PCI_AUXDEV
+	bool "xHCI PCI auxiliary device support"
+	depends on USB_XHCI_PCI
+	select AUXILIARY_BUS
+	help
+	  This enables xHCI PCI support for registering auxiliary devices
+	  for selected controllers. It is used by optional child drivers
+	  that bind to xHCI PCI controller-specific functionality through
+	  the auxiliary bus.
+
 config USB_XHCI_PCI_RENESAS
 	tristate "Support for additional Renesas xHCI controller with firmware"
 	depends on USB_XHCI_PCI
diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
index 585b2f3117b0..1ab27d2182eb 100644
--- a/drivers/usb/host/xhci-pci.c
+++ b/drivers/usb/host/xhci-pci.c
@@ -8,6 +8,8 @@
  * Some code borrowed from the Linux EHCI driver.
  */
 
+#include <linux/auxiliary_bus.h>
+#include <linux/device/devres.h>
 #include <linux/pci.h>
 #include <linux/slab.h>
 #include <linux/module.h>
@@ -103,6 +105,114 @@ static int xhci_pci_run(struct usb_hcd *hcd);
 static int xhci_pci_update_hub_device(struct usb_hcd *hcd, struct usb_device *hdev,
 				      struct usb_tt *tt, gfp_t mem_flags);
 
+#if IS_ENABLED(CONFIG_USB_XHCI_PCI_AUXDEV)
+static const struct {
+	struct pci_device_id id;
+	const char *aux_dev_name;
+} pci_ids_have_aux[] = {
+	{
+		.id = { PCI_DEVICE(PCI_VENDOR_ID_AMD, 0x43fd) }, /* PROM21 xHCI */
+		.aux_dev_name = "hwmon",
+	},
+	{ /* end: all zeroes */ }
+};
+
+struct xhci_pci_aux_devres {
+	struct auxiliary_device *auxdev;
+};
+
+static bool xhci_pci_aux_match_id(const struct pci_device_id *id,
+				  const struct pci_dev *pdev)
+{
+	if (id->vendor != PCI_ANY_ID && id->vendor != pdev->vendor)
+		return false;
+	if (id->device != PCI_ANY_ID && id->device != pdev->device)
+		return false;
+	if (id->subvendor != PCI_ANY_ID &&
+	    id->subvendor != pdev->subsystem_vendor)
+		return false;
+	if (id->subdevice != PCI_ANY_ID &&
+	    id->subdevice != pdev->subsystem_device)
+		return false;
+
+	return !((id->class ^ pdev->class) & id->class_mask);
+}
+
+static const char *xhci_pci_aux_dev_name(struct pci_dev *pdev)
+{
+	int i;
+
+	for (i = 0; pci_ids_have_aux[i].aux_dev_name; i++) {
+		if (xhci_pci_aux_match_id(&pci_ids_have_aux[i].id, pdev))
+			return pci_ids_have_aux[i].aux_dev_name;
+	}
+
+	return NULL;
+}
+
+static void xhci_pci_aux_devres_release(struct device *dev, void *res)
+{
+	struct xhci_pci_aux_devres *devres = res;
+
+	if (devres->auxdev)
+		auxiliary_device_destroy(devres->auxdev);
+}
+
+static void xhci_pci_try_add_aux_device(struct pci_dev *pdev)
+{
+	struct xhci_pci_aux_devres *devres;
+	struct auxiliary_device *auxdev;
+	const char *aux_dev_name;
+
+	aux_dev_name = xhci_pci_aux_dev_name(pdev);
+	if (!aux_dev_name)
+		return;
+
+	devres = devres_alloc(xhci_pci_aux_devres_release, sizeof(*devres),
+			      GFP_KERNEL);
+	if (!devres) {
+		dev_warn(&pdev->dev,
+			 "failed to allocate auxiliary device state\n");
+		return;
+	}
+
+	auxdev = auxiliary_device_create(&pdev->dev, KBUILD_MODNAME,
+					 aux_dev_name, NULL,
+					 (pci_domain_nr(pdev->bus) << 16) |
+						 pci_dev_id(pdev));
+	if (!auxdev) {
+		devres_free(devres);
+		dev_warn(&pdev->dev, "failed to add %s auxiliary device\n",
+			 aux_dev_name);
+		return;
+	}
+
+	devres->auxdev = auxdev;
+	devres_add(&pdev->dev, devres);
+}
+
+static void xhci_pci_try_remove_aux_device(struct pci_dev *pdev)
+{
+	struct xhci_pci_aux_devres *devres;
+
+	devres = devres_find(&pdev->dev, xhci_pci_aux_devres_release, NULL,
+			     NULL);
+	if (!devres || !devres->auxdev)
+		return;
+
+	auxiliary_device_destroy(devres->auxdev);
+	devres->auxdev = NULL;
+}
+#else
+static inline void xhci_pci_try_add_aux_device(struct pci_dev *pdev)
+{
+}
+
+static inline void xhci_pci_try_remove_aux_device(struct pci_dev *pdev)
+{
+}
+#endif
+
 static const struct xhci_driver_overrides xhci_pci_overrides __initconst = {
 	.reset = xhci_pci_setup,
 	.start = xhci_pci_run,
@@ -677,6 +787,8 @@ int xhci_pci_common_probe(struct pci_dev *dev, const struct pci_device_id *id)
 	if (device_property_read_bool(&dev->dev, "ti,pwron-active-high"))
 		pci_clear_and_set_config_dword(dev, 0xE0, 0, 1 << 22);
 
+	xhci_pci_try_add_aux_device(dev);
+
 	return 0;
 
 put_usb3_hcd:
@@ -713,6 +825,8 @@ void xhci_pci_remove(struct pci_dev *dev)
 	xhci = hcd_to_xhci(pci_get_drvdata(dev));
 	set_power_d3 = xhci->quirks & XHCI_SPURIOUS_WAKEUP;
 
+	xhci_pci_try_remove_aux_device(dev);
+
 	xhci->xhc_state |= XHCI_STATE_REMOVING;
 
 	if (pci_choose_state(dev, PMSG_SUSPEND) == PCI_D0)
-- 
2.53.0