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

[Mario Limonciello <mario.limonciello@amd.com>]

On 5/6/26 15:40, Jihong Min wrote:
> [You don't often get email from hurryman2212@gmail.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> 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);

What's wrong with pci_match_id()?

> +}
> +
> +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
>