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

["Bernatowicz, Marcin" <marcin.bernatowicz@linux.intel.com>]

On 2/9/2026 11:16 AM, Laguna, Lukasz wrote:
>
> 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.

driver/driver_len are optional, callers may pass NULL and/or 0 when they 
only need the

return value (bound/unbound) and don’t care about the driver name...

>
>> +        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