Re: [PATCH v3 i-g-t 2/7] lib/igt_pci: Add generic PCI driver override and bind/unbind helpers

["Laguna, Lukasz" <lukasz.laguna@intel.com>]

On 2/4/2026 17:32, Marcin Bernatowicz wrote:
> Add generic helpers for controlling PCI driver binding via sysfs.
>
> The new APIs provide driver- and device-centric primitives for:
>    - setting and clearing driver_override
>    - triggering PCI driver reprobe
>    - binding and unbinding devices to a specific PCI driver
>    - query the currently bound PCI driver
>
> Signed-off-by: Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>
> Cc: Adam Miszczak <adam.miszczak@linux.intel.com>
> Cc: Jakub Kolakowski <jakub1.kolakowski@intel.com>
> Cc: Kamil Konieczny <kamil.konieczny@linux.intel.com>
> Cc: Lukasz Laguna <lukasz.laguna@intel.com>
>
> ---
> v2:
> - Add igt_pci_get_bound_driver_name() to query the currently bound PCI
>    driver via the /sys/bus/pci/devices/<BDF>/driver symlink.
> - Extend igt_pci_bind_driver_override() and igt_pci_unbind_driver_override()
>    with a timeout_ms parameter so callers can wait for bind/unbind to
>    actually complete, instead of relying on drivers_probe write success.
>
> ---
>   lib/igt_pci.c | 351 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   lib/igt_pci.h |  13 +-
>   2 files changed, 363 insertions(+), 1 deletion(-)
>
> diff --git a/lib/igt_pci.c b/lib/igt_pci.c
> index 61aaf939d..80aaf07c5 100644
> --- a/lib/igt_pci.c
> +++ b/lib/igt_pci.c
> @@ -3,9 +3,18 @@
>    * Copyright © 2022 Intel Corporation
>    */
>   
> +#include <ctype.h>
> +#include <dirent.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <limits.h>
> +#include <string.h>
> +#include <unistd.h>
>   #include <pciaccess.h>
> +#include "igt_aux.h"
>   #include "igt_core.h"
>   #include "igt_pci.h"
> +#include "igt_sysfs.h"
>   
>   static int find_pci_cap_offset_at(struct pci_device *dev, enum pci_cap_id cap_id,
>   				  int start_offset)
> @@ -51,3 +60,345 @@ int find_pci_cap_offset(struct pci_device *dev, enum pci_cap_id cap_id)
>   {
>   	return find_pci_cap_offset_at(dev, cap_id, PCI_CAPS_START);
>   }
> +
> +static int open_pci_driver_dir(const char *driver)
> +{
> +	char path[PATH_MAX];
> +
> +	snprintf(path, sizeof(path), "/sys/bus/pci/drivers/%s", driver);
> +	return open(path, O_RDONLY | O_CLOEXEC);
> +}
> +
> +/**
> + * igt_pci_device_unbind:
> + * @pci_slot: BDF like "0000:01:00.0"
> + *
> + * Unbind @pci_slot from its currently bound driver, if any.
> + * Returns 0 on success, or a negative errno-like value.
> + */
> +int igt_pci_device_unbind(const char *pci_slot)
> +{
> +	char path[PATH_MAX];
> +	int dirfd;
> +	int ret;
> +
> +	snprintf(path, sizeof(path), "/sys/bus/pci/devices/%s/driver", pci_slot);
> +	dirfd = open(path, O_RDONLY | O_CLOEXEC);
> +	if (dirfd < 0)
> +		return 0; /* already unbound */
> +
> +	ret = igt_sysfs_set(dirfd, "unbind", pci_slot) ? 0 : -errno;
> +	close(dirfd);
> +
> +	return ret;
> +}
> +
> +/**
> + * igt_pci_driver_bind:
> + * @driver: PCI driver name under /sys/bus/pci/drivers/<driver>
> + * @pci_slot: device to bind
> + *
> + * Bind @pci_slot to @driver. Driver must be present/loaded.
> + * Returns 0 on success, or a negative errno-like value.
> + */
> +int igt_pci_driver_bind(const char *driver, const char *pci_slot)
> +{
> +	int dirfd, ret;
> +
> +	dirfd = open_pci_driver_dir(driver);
> +	if (dirfd < 0)
> +		return -errno;
> +
> +	ret = igt_sysfs_set(dirfd, "bind", pci_slot) ? 0 : -errno;
> +	close(dirfd);
> +
> +	return ret;
> +}
> +
> +/**
> + * igt_pci_driver_unbind:
> + * @driver: PCI driver name
> + * @pci_slot: device to unbind
> + *
> + * Unbind @pci_slot from @driver.
> + * Returns 0 on success, or a negative errno-like value.
> + */
> +int igt_pci_driver_unbind(const char *driver, const char *pci_slot)
> +{
> +	int dirfd, ret;
> +
> +	dirfd = open_pci_driver_dir(driver);
> +	if (dirfd < 0)
> +		return -errno;
> +
> +	ret = igt_sysfs_set(dirfd, "unbind", pci_slot) ? 0 : -errno;
> +	close(dirfd);
> +
> +	return ret;
> +}
> +
> +/**
> + * igt_pci_driver_unbind_all:
> + * @driver: PCI driver name
> + *
> + * Unbind all devices currently bound to @driver.
> + * Returns 0 on success, or a negative errno-like value.
> + */
> +int igt_pci_driver_unbind_all(const char *driver)
> +{
> +	char path[PATH_MAX];
> +	DIR *dir;
> +	struct dirent *de;
> +	int driver_fd;
> +
> +	snprintf(path, sizeof(path), "/sys/bus/pci/drivers/%s", driver);
> +	dir = opendir(path);
> +	if (!dir)
> +		return -errno;
> +
> +	driver_fd = dirfd(dir);
> +
> +	while ((de = readdir(dir))) {
> +		bool ok;
> +
> +		/* BDF symlinks are like "0000:01:00.0" and start with digit */
> +		if (de->d_type != DT_LNK || !isdigit(de->d_name[0]))
> +			continue;
> +
> +		ok = igt_sysfs_set(driver_fd, "unbind", de->d_name);
> +		if (!ok) {
> +			int err = -errno;
> +
> +			closedir(dir);
> +			return err;
> +		}
> +	}
> +
> +	closedir(dir);
> +	return 0;
> +}
> +
> +/**
> + * igt_pci_set_driver_override:
> + * @pci_slot: PCI device BDF (e.g. "0000:01:00.0")
> + * @driver: PCI driver name to force-bind (e.g. "xe-vfio-pci"), or
> + *          NULL / empty string to clear an existing override
> + *
> + * Set or clear the PCI driver_override for @pci_slot via sysfs.
> + *
> + * This does not trigger driver reprobe by itself. Call
> + * igt_pci_probe_drivers() afterwards to apply the override.
> + *
> + * Returns: 0 on success, negative errno on failure.
> + */
> +int igt_pci_set_driver_override(const char *pci_slot, const char *driver)
> +{
> +	char devpath[PATH_MAX];
> +	int dev;
> +	bool ok;
> +
> +	snprintf(devpath, sizeof(devpath), "/sys/bus/pci/devices/%s", pci_slot);
> +	dev = open(devpath, O_DIRECTORY | O_RDONLY);
> +	if (dev < 0)
> +		return -errno;
> +
> +	ok = igt_sysfs_set(dev, "driver_override", driver ? driver : "");
> +	close(dev);
> +
> +	return ok ? 0 : -errno;
> +}
> +
> +/**
> + * igt_pci_probe_drivers:
> + * @pci_slot: PCI device BDF (e.g. "0000:01:00.0")
> + *
> + * Trigger PCI driver reprobe for @pci_slot by writing to
> + * /sys/bus/pci/drivers_probe.
> + *
> + * This causes the kernel to attempt binding the device, honoring any
> + * driver_override previously set.
> + *
> + * Note: a successful write only means the reprobe request was accepted.
> + * It does not guarantee that a driver actually bound to the device.
> + *
> + * Returns: 0 on success, negative errno on failure.
> + */
> +int igt_pci_probe_drivers(const char *pci_slot)
> +{
> +	int pci;
> +	bool ok;
> +
> +	pci = open("/sys/bus/pci", O_DIRECTORY | O_RDONLY);
> +	if (pci < 0)
> +		return -errno;
> +
> +	ok = igt_sysfs_set(pci, "drivers_probe", pci_slot);
> +	close(pci);
> +
> +	return ok ? 0 : -errno;
> +}
> +
> +/**
> + * igt_pci_get_bound_driver_name:
> + * @pci_slot: PCI device BDF (e.g. "0000:01:00.0")
> + * @driver: destination buffer for the bound driver name
> + * @driver_len: size of @driver in bytes
> + *
> + * Read the currently bound PCI driver name for @pci_slot by inspecting the
> + * /sys/bus/pci/devices/<BDF>/driver symlink.
> + *
> + * Return values:
> + *  1: device is bound and @driver contains the driver name
> + *  0: device is unbound (no driver symlink)
> + * <0: negative errno-like value on error
> + */
> +int igt_pci_get_bound_driver_name(const char *pci_slot, char *driver, size_t driver_len)
> +{
> +	char path[PATH_MAX];
> +	char link[PATH_MAX];
> +	const char *base;
> +	ssize_t len;
> +
> +	if (driver && driver_len)
> +		driver[0] = '\0';
> +
> +	snprintf(path, sizeof(path), "/sys/bus/pci/devices/%s/driver", pci_slot);
> +	len = readlink(path, link, sizeof(link) - 1);
> +	if (len < 0) {
> +		if (errno == ENOENT)
> +			return 0; /* unbound */
> +
> +		return -errno;
> +	}
> +
> +	link[len] = '\0';
> +	base = strrchr(link, '/');
> +	base = base ? base + 1 : link;
> +
> +	if (driver && driver_len)

You can check the input params at the beginning of the function and 
return error if they are invalid.

> +		snprintf(driver, driver_len, "%s", base);
> +
> +	return 1;
> +}
> +
> +/**
> + * igt_pci_bind_driver_override:
> + * @pci_slot: PCI device BDF (e.g. "0000:01:00.0")
> + * @driver: PCI driver name to bind (must not be NULL or empty)
> + * @timeout_ms: how long to wait for the device to become bound.
> + *              If 0, don't wait (best-effort immediate check only).
> + *
> + * Bind @pci_slot to @driver using the driver_override mechanism.
> + *
> + * This helper sets driver_override and immediately triggers driver
> + * reprobe so that the device is bound to the requested driver.
> + *
> + * Returns: 0 on success, negative errno-like value on failure.
> + * A reprobe request can be accepted by sysfs while the driver probe
> + * fails later; this helper verifies the device ended up bound.
> + *
> + * On bind failure, returns a negative error and the failure reason may
> + * also be logged to dmesg by the kernel driver.
> + */
> +int igt_pci_bind_driver_override(const char *pci_slot, const char *driver,
> +				 unsigned int timeout_ms)
> +{
> +	int ret;
> +	char bound[64];
> +	int bound_ret;
> +	bool bound_ok;
> +
> +	if (!driver || !driver[0])
> +		return -EINVAL;
> +
> +	ret = igt_pci_set_driver_override(pci_slot, driver);
> +	if (ret)
> +		return ret;
> +
> +	ret = igt_pci_probe_drivers(pci_slot);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Writing to drivers_probe only tells us the kernel accepted the request.
> +	 * The actual driver probe may still fail (and only be reported via dmesg).
> +	 * Verify that the device ended up bound to the requested driver.
> +	 */
> +	bound_ret = igt_pci_get_bound_driver_name(pci_slot, bound, sizeof(bound));
> +	if (bound_ret < 0)
> +		return bound_ret;
> +
> +	if (timeout_ms == 0) {
> +		/*
> +		 * No waiting requested. If the device is already bound, validate
> +		 * it is bound to the expected driver; otherwise treat as
> +		 * best-effort request-only success.
> +		 */
> +		if (bound_ret > 0 && strcmp(bound, driver))
> +			return -EBUSY;
> +
> +		return 0;
> +	}
> +
> +	bound_ok = igt_wait((bound_ret =
> +			     igt_pci_get_bound_driver_name(pci_slot, bound, sizeof(bound))) != 0,
> +			    timeout_ms, 1);
> +	if (!bound_ok)
> +		return -EIO;
> +
> +	if (bound_ret < 0)
> +		return bound_ret;
> +
> +	if (strcmp(bound, driver))
> +		return -EBUSY;
> +
> +	return 0;
> +}
> +
> +/**
> + * igt_pci_unbind_driver_override:
> + * @pci_slot: PCI device BDF (e.g. "0000:01:00.0")
> + * @timeout_ms: how long to wait for the device to become unbound.
> + *              If 0, don't wait (best-effort immediate check only).
> + *
> + * Unbind @pci_slot from its currently bound driver (if any) and clear
> + * any driver_override setting.
> + *
> + * This is the inverse operation of igt_pci_bind_driver_override().
> + *
> + * Returns: 0 on success, negative errno on failure.
> + */
> +int igt_pci_unbind_driver_override(const char *pci_slot, unsigned int timeout_ms)
> +{
> +	int ret;
> +	int bound_ret;
> +	char bound[64];
> +	bool unbound_ok;
> +
> +	ret = igt_pci_device_unbind(pci_slot);
> +	if (ret)
> +		return ret;
> +
> +	ret = igt_pci_set_driver_override(pci_slot, "");
> +	if (ret)
> +		return ret;
> +
> +	bound_ret = igt_pci_get_bound_driver_name(pci_slot, bound, sizeof(bound));
> +	if (bound_ret < 0)
> +		return bound_ret;
> +
> +	if (timeout_ms == 0)
> +		return 0;
> +
> +	/* Verify the device actually ends up unbound (driver symlink removed). */
> +	unbound_ok = igt_wait((bound_ret =
> +			       igt_pci_get_bound_driver_name(pci_slot, bound, sizeof(bound))) == 0,
> +			      timeout_ms, 1);
> +	if (!unbound_ok)
> +		return -EBUSY;
> +
> +	if (bound_ret < 0)
> +		return bound_ret;
> +
> +	return 0;
> +}
> diff --git a/lib/igt_pci.h b/lib/igt_pci.h
> index 92b9cc392..a66eeebf2 100644
> --- a/lib/igt_pci.h
> +++ b/lib/igt_pci.h
> @@ -6,8 +6,9 @@
>   #ifndef __IGT_PCI_H__
>   #define __IGT_PCI_H__
>   
> -#include <stdint.h>
>   #include <endian.h>
> +#include <stddef.h>
> +#include <stdint.h>
>   
>   /* forward declaration */
>   struct pci_device;
> @@ -24,5 +25,15 @@ enum pci_cap_id {
>   #define  PCI_SLOT_PWR_CTRL_PRESENT (1 << 1)
>   
>   int find_pci_cap_offset(struct pci_device *dev, enum pci_cap_id cap_id);
> +int igt_pci_device_unbind(const char *pci_slot);
> +int igt_pci_driver_bind(const char *driver, const char *pci_slot);
> +int igt_pci_driver_unbind(const char *driver, const char *pci_slot);
> +int igt_pci_driver_unbind_all(const char *driver);
> +int igt_pci_set_driver_override(const char *pci_slot, const char *driver);
> +int igt_pci_probe_drivers(const char *pci_slot);
> +int igt_pci_get_bound_driver_name(const char *pci_slot, char *driver, size_t driver_len);
> +int igt_pci_bind_driver_override(const char *pci_slot, const char *driver,
> +				 unsigned int timeout_ms);
> +int igt_pci_unbind_driver_override(const char *pci_slot, unsigned int timeout_ms);
>   
>   #endif