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    Subject[PATCH v4 20/22] driver core: Allow deferring probes until late init
    Date
    Add a field to struct device that instructs the device-driver core to
    defer the probe of this device until the late_initcall level.

    By letting all built-in drivers to register before starting to probe, we
    can avoid any deferred probes by probing dependencies on demand.

    Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>

    ---

    Changes in v4:
    - Add Kconfig DELAY_DEVICE_PROBES to allow disabling delayed probing in
    machines with initcalls that depend on devices probing at a given time.

    Changes in v3: None
    Changes in v2: None

    drivers/base/Kconfig | 18 ++++++++++++++++++
    drivers/base/dd.c | 7 +++++++
    include/linux/device.h | 2 ++
    3 files changed, 27 insertions(+)

    diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
    index 98504ec99c7d..44b5d33b1f49 100644
    --- a/drivers/base/Kconfig
    +++ b/drivers/base/Kconfig
    @@ -324,4 +324,22 @@ config CMA_ALIGNMENT

    endif

    +config DELAY_DEVICE_PROBES
    + bool "Allow delaying the probe of some devices"
    + default y
    + help
    + Devices can be matched to a driver and probed from the moment they
    + are registered, but early during boot their probes are likely to be
    + deferred because some dependency isn't available yet because most
    + drivers haven't been registered yet.
    +
    + Enabling this option allows the device registration code to delay the
    + probing of a specific device until device_initcall_sync, when all
    + built-in drivers have been registered already.
    +
    + In some platforms there may be implicit assumptions about when some
    + devices are probed, so enabling this option could cause problems there.
    +
    + If unsure, say Y here.
    +
    endmenu
    diff --git a/drivers/base/dd.c b/drivers/base/dd.c
    index faf60bfc46b3..0654fb771a53 100644
    --- a/drivers/base/dd.c
    +++ b/drivers/base/dd.c
    @@ -417,6 +417,13 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
    if (!device_is_registered(dev))
    return -ENODEV;

    +#if IS_ENABLED(CONFIG_DELAY_DEVICE_PROBES)
    + if (!driver_deferred_probe_enable && dev->probe_late) {
    + driver_deferred_probe_add(dev);
    + return 0;
    + }
    +#endif
    +
    pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
    drv->bus->name, __func__, dev_name(dev), drv->name);

    diff --git a/include/linux/device.h b/include/linux/device.h
    index d8be07bc9c3f..fe5c50ffd7d3 100644
    --- a/include/linux/device.h
    +++ b/include/linux/device.h
    @@ -748,6 +748,7 @@ struct device_dma_parameters {
    *
    * @offline_disabled: If set, the device is permanently online.
    * @offline: Set after successful invocation of bus type's .offline().
    + * @probe_late: If set, device will be probed in the late initcall level.
    *
    * At the lowest level, every device in a Linux system is represented by an
    * instance of struct device. The device structure contains the information
    @@ -832,6 +833,7 @@ struct device {

    bool offline_disabled:1;
    bool offline:1;
    + bool probe_late:1;
    };

    static inline struct device *kobj_to_dev(struct kobject *kobj)
    --
    2.4.3


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