On 9/29/2015 2:10 AM, Tomeu Vizoso wrote:
> 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.viz...@collabora.com>
>
> ---
>
> Changes in v7:
> - Move IS_ENABLED(CONFIG_DELAY_DEVICE_PROBES) into if condition
> - Hide CONFIG_DELAY_DEVICE_PROBES behind EXPERT
>
> 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.
>
> drivers/base/Kconfig | 18 ++++++++++++++++++
> drivers/base/dd.c | 6 ++++++
> include/linux/device.h | 2 ++
> 3 files changed, 26 insertions(+)
>
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 98504ec99c7d..8bb7b556da1b 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" if EXPERT
> + 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
^^^^^^^^^^^^^^^^^^^^
late_initcall
> + 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 7dc04ee81c8b..c4a3f298e726 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -417,6 +417,12 @@ 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) &&
> + !driver_deferred_probe_enable && dev->probe_late) {
> + driver_deferred_probe_add(dev);
> + return 0;
> + }
> +
> 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 8e7b806f0744..e64f4c7e243d 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -744,6 +744,7 @@ 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
> @@ -828,6 +829,7 @@ struct device {
>
> bool offline_disabled:1;
> bool offline:1;
> + bool probe_late:1;
> };
>
> static inline struct device *kobj_to_dev(struct kobject *kobj)
>
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