[PATCH v4 20/22] driver core: Allow deferring probes until late init

From: Tomeu Vizoso
Date: Mon Sep 07 2015 - 08:27:49 EST

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@xxxxxxxxxxxxx>


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


+ 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.
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 (!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 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)

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