Re: [PATCH v4 1/2] usb: xhci-pci: add AMD Promontory 21 PCI glue

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

On 5/8/26 09:39, Jihong Min wrote:
> AMD Promontory 21 (PROM21) xHCI controllers use generic xHCI
> operation, but the PCI function also exposes optional
> controller-specific sensor functionality. Add a small PROM21 PCI glue
> driver for AMD 1022:43fd controllers.
> 
> The driver delegates USB host operation to the common xhci-pci core and
> creates a "hwmon" auxiliary device for optional child drivers. Failure
> to create the auxiliary device is logged but does not fail the xHCI
> probe, since the auxiliary device is only needed for sensor support.
> 
> Keep the PROM21 PCI glue built-in only when enabled because it owns the
> PCI binding for PROM21 xHCI controllers and must be available whenever
> the common built-in xhci-pci driver hands those controllers off. This
> avoids an early boot case where generic xhci-pci rejects a PROM21
> controller but a modular xhci-pci-prom21 driver is not available in the
> initramfs, leaving USB devices behind that controller unavailable.
> 
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Jihong Min <hurryman2212@gmail.com>
> ---
>   drivers/usb/host/Kconfig           |  18 +++++
>   drivers/usb/host/Makefile          |   1 +
>   drivers/usb/host/xhci-pci-prom21.c | 111 +++++++++++++++++++++++++++++
>   drivers/usb/host/xhci-pci.c        |  11 +++
>   4 files changed, 141 insertions(+)
>   create mode 100644 drivers/usb/host/xhci-pci-prom21.c
> 
> diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
> index 0a277a07cf70..74eedef1440d 100644
> --- a/drivers/usb/host/Kconfig
> +++ b/drivers/usb/host/Kconfig
> @@ -42,6 +42,24 @@ config USB_XHCI_PCI
>   	depends on USB_PCI
>   	default y
>   
> +config USB_XHCI_PCI_PROM21
> +	bool "AMD Promontory 21 xHCI PCI support"
> +	depends on USB_XHCI_PCI=y
> +	select AUXILIARY_BUS
> +	help
> +	  Say 'Y' to enable support for the AMD Promontory 21 xHCI PCI
> +	  controller with optional sensor support. This driver does not add
> +	  PROM21-specific USB or xHCI operation. It binds PROM21 xHCI PCI
> +	  functions, delegates USB host operation to the common xHCI PCI core,
> +	  and creates auxiliary devices for optional sensor drivers.
> +
> +	  This driver is built-in only because it owns the PCI binding for
> +	  PROM21 xHCI controllers when enabled and must be available whenever
> +	  the common xHCI PCI driver is available. The optional sensor driver
> +	  can still be built as a module.
> +
> +	  If unsure, say 'N'.
> +
>   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/Makefile b/drivers/usb/host/Makefile
> index a07e7ba9cd53..174580c1281a 100644
> --- a/drivers/usb/host/Makefile
> +++ b/drivers/usb/host/Makefile
> @@ -71,6 +71,7 @@ obj-$(CONFIG_USB_UHCI_HCD)	+= uhci-hcd.o
>   obj-$(CONFIG_USB_FHCI_HCD)	+= fhci.o
>   obj-$(CONFIG_USB_XHCI_HCD)	+= xhci-hcd.o
>   obj-$(CONFIG_USB_XHCI_PCI)	+= xhci-pci.o
> +obj-$(CONFIG_USB_XHCI_PCI_PROM21)	+= xhci-pci-prom21.o
>   obj-$(CONFIG_USB_XHCI_PCI_RENESAS)	+= xhci-pci-renesas.o
>   obj-$(CONFIG_USB_XHCI_PLATFORM) += xhci-plat-hcd.o
>   obj-$(CONFIG_USB_XHCI_HISTB)	+= xhci-histb.o
> diff --git a/drivers/usb/host/xhci-pci-prom21.c b/drivers/usb/host/xhci-pci-prom21.c
> new file mode 100644
> index 000000000000..7354a898732e
> --- /dev/null
> +++ b/drivers/usb/host/xhci-pci-prom21.c
> @@ -0,0 +1,111 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * AMD Promontory 21 xHCI host controller PCI Bus Glue.
> + *
> + * This does not add any PROM21-specific USB or xHCI operation. It exists only
> + * to publish an auxiliary device for integrated temperature sensor support.
> + *
> + * Copyright (C) 2026 Jihong Min <hurryman2212@gmail.com>
> + */
> +
> +#include <linux/auxiliary_bus.h>
> +#include <linux/device/devres.h>
> +#include <linux/errno.h>
> +#include <linux/module.h>
> +#include <linux/pci.h>
> +#include <linux/slab.h>
> +#include <linux/usb.h>
> +#include <linux/usb/hcd.h>
> +
> +#include "xhci-pci.h"
> +
> +struct prom21_xhci_auxdev {
> +	struct auxiliary_device *auxdev;
> +};
> +
> +static void prom21_xhci_auxdev_release(struct device *dev, void *res)
> +{
> +	struct prom21_xhci_auxdev *prom21_auxdev = res;
> +
> +	auxiliary_device_destroy(prom21_auxdev->auxdev);
> +}
> +
> +static int prom21_xhci_create_auxdev(struct pci_dev *pdev)
> +{
> +	struct prom21_xhci_auxdev *prom21_auxdev;
> +
> +	prom21_auxdev = devres_alloc(prom21_xhci_auxdev_release,
> +				     sizeof(*prom21_auxdev), GFP_KERNEL);
> +	if (!prom21_auxdev)
> +		return -ENOMEM;
> +
> +	prom21_auxdev->auxdev =
> +		auxiliary_device_create(&pdev->dev, KBUILD_MODNAME, "hwmon",
> +					NULL, (pci_domain_nr(pdev->bus) << 16) |
> +						      pci_dev_id(pdev));
> +	if (!prom21_auxdev->auxdev) {
> +		devres_free(prom21_auxdev);
> +		return -ENOMEM;
> +	}
> +
> +	devres_add(&pdev->dev, prom21_auxdev);
> +	return 0;
> +}
> +
> +static void prom21_xhci_destroy_auxdev(struct pci_dev *pdev)
> +{
> +	devres_release(&pdev->dev, prom21_xhci_auxdev_release, NULL, NULL);
> +}
> +
> +static int prom21_xhci_probe(struct pci_dev *dev,
> +			     const struct pci_device_id *id)
> +{
> +	int retval;
> +
> +	retval = xhci_pci_common_probe(dev, id);
> +	if (retval)
> +		return retval;
> +
> +	retval = prom21_xhci_create_auxdev(dev);
> +	if (retval) {
> +		/*
> +		 * The auxiliary device only provides optional temperature sensor
> +		 * support. Keep the xHCI controller usable if it fails.
> +		 */
> +		dev_err(&dev->dev,
> +			"failed to create PROM21 hwmon auxiliary device: %d\n",
> +			retval);
> +	}
> +
> +	return 0;
> +}
> +
> +static void prom21_xhci_remove(struct pci_dev *dev)
> +{
> +	prom21_xhci_destroy_auxdev(dev);
> +	xhci_pci_remove(dev);
> +}
> +
> +static const struct pci_device_id pci_ids[] = {
> +	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, 0x43fd) }, /* PROM21 xHCI */
> +	{ /* end: all zeroes */ }
> +};
> +MODULE_DEVICE_TABLE(pci, pci_ids);
> +
> +static struct pci_driver prom21_xhci_driver = {
> +	.name = "xhci-pci-prom21",
> +	.id_table = pci_ids,
> +
> +	.probe = prom21_xhci_probe,
> +	.remove = prom21_xhci_remove,
> +
> +	.shutdown = usb_hcd_pci_shutdown,
> +	.driver = {
> +		.pm = pm_ptr(&usb_hcd_pci_pm_ops),
> +	},
> +};
> +module_pci_driver(prom21_xhci_driver);
> +
> +MODULE_DESCRIPTION("AMD Promontory 21 xHCI PCI Host Controller Driver");
> +MODULE_IMPORT_NS("xhci");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
> index 585b2f3117b0..5db427ad0422 100644
> --- a/drivers/usb/host/xhci-pci.c
> +++ b/drivers/usb/host/xhci-pci.c
> @@ -84,6 +84,7 @@
>   #define PCI_DEVICE_ID_AMD_PROMONTORYA_3			0x43ba
>   #define PCI_DEVICE_ID_AMD_PROMONTORYA_2			0x43bb
>   #define PCI_DEVICE_ID_AMD_PROMONTORYA_1			0x43bc
> +#define PCI_DEVICE_ID_AMD_PROM21_XHCI			0x43fd

This define should be in a common header used by xhci-pci.c and 
xhci-pci-prom21.c both.

>   
>   #define PCI_DEVICE_ID_ATI_NAVI10_7316_XHCI		0x7316
>   
> @@ -696,12 +697,22 @@ static const struct pci_device_id pci_ids_renesas[] = {
>   	{ /* end: all zeroes */ }
>   };
>   
> +/* handled by xhci-pci-prom21 if enabled */
> +static const struct pci_device_id pci_ids_prom21[] = {
> +	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_PROM21_XHCI) },
> +	{ /* end: all zeroes */ }
> +};
> +
>   static int xhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
>   {
>   	if (IS_ENABLED(CONFIG_USB_XHCI_PCI_RENESAS) &&
>   			pci_match_id(pci_ids_renesas, dev))
>   		return -ENODEV;
>   
> +	if (IS_ENABLED(CONFIG_USB_XHCI_PCI_PROM21) &&
> +	    pci_match_id(pci_ids_prom21, dev))
> +		return -ENODEV;
> +
>   	return xhci_pci_common_probe(dev, id);
>   }
>