[PATCH v3 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 PCI ID match table lists AMD Promontory 21 (PROM21) 1022:43fd
controllers. For matching controllers, xhci-pci creates an auxiliary
device and stores it in devres so the remove path destroys it before HCD
teardown.

Subsystem-specific child drivers can then bind to those devices through
the auxiliary bus and keep their hardware-specific logic outside xhci-pci.

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 | 83 +++++++++++++++++++++++++++++++++++++
 2 files changed, 93 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..618d6840e108 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>
@@ -80,6 +82,7 @@
 #define PCI_DEVICE_ID_AMD_RAVEN_15E1_XHCI		0x15e1
 #define PCI_DEVICE_ID_AMD_RAVEN2_XHCI			0x15e5
 #define PCI_DEVICE_ID_AMD_RENOIR_XHCI			0x1639
+#define PCI_DEVICE_ID_AMD_PROM21_XHCI			0x43fd
 #define PCI_DEVICE_ID_AMD_PROMONTORYA_4			0x43b9
 #define PCI_DEVICE_ID_AMD_PROMONTORYA_3			0x43ba
 #define PCI_DEVICE_ID_AMD_PROMONTORYA_2			0x43bb
@@ -103,6 +106,80 @@ 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);
 
+static const struct pci_device_id pci_ids_have_aux[] = {
+	{ PCI_DEVICE_DATA(AMD, PROM21_XHCI, "prom21_hwmon") },
+	{ /* end: all zeroes */ }
+};
+
+struct xhci_pci_aux_devres {
+	struct auxiliary_device *auxdev;
+};
+
+static const char *xhci_pci_aux_dev_name(struct pci_dev *pdev)
+{
+	const struct pci_device_id *id;
+
+	id = pci_match_id(pci_ids_have_aux, pdev);
+	if (!id)
+		return NULL;
+
+	return (const char *)id->driver_data;
+}
+
+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;
+}
+
 static const struct xhci_driver_overrides xhci_pci_overrides __initconst = {
 	.reset = xhci_pci_setup,
 	.start = xhci_pci_run,
@@ -677,6 +754,9 @@ 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);
 
+	if (IS_ENABLED(CONFIG_USB_XHCI_PCI_AUXDEV))
+		xhci_pci_try_add_aux_device(dev);
+
 	return 0;
 
 put_usb3_hcd:
@@ -713,6 +793,9 @@ void xhci_pci_remove(struct pci_dev *dev)
 	xhci = hcd_to_xhci(pci_get_drvdata(dev));
 	set_power_d3 = xhci->quirks & XHCI_SPURIOUS_WAKEUP;
 
+	if (IS_ENABLED(CONFIG_USB_XHCI_PCI_AUXDEV))
+		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