diff mbox

[v7,1/2] drivers: base: add support for registering notifier about deferred probe

Message ID 1460540160-18762-2-git-send-email-m.szyprowski@samsung.com
State New
Headers show

Commit Message

Marek Szyprowski April 13, 2016, 9:35 a.m. UTC 
This patch adds code which allow other subsystems get a notification
when deferred probe has been triggered. This way one can retry some
actions, which earlier failed with -EPROBE_DEFER error code.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

---
 drivers/base/dd.c      | 31 +++++++++++++++++++++++++++++++
 include/linux/device.h |  3 +++
 2 files changed, 34 insertions(+)

-- 
1.9.2

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Comments

Marek Szyprowski April 14, 2016, 7:36 a.m. UTC | #1 
Hello,

On 2016-04-13 16:12, Greg Kroah-Hartman wrote:
> On Wed, Apr 13, 2016 at 11:35:59AM +0200, Marek Szyprowski wrote:

>> This patch adds code which allow other subsystems get a notification

>> when deferred probe has been triggered. This way one can retry some

>> actions, which earlier failed with -EPROBE_DEFER error code.

>>

>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

> Why would some other subsystem want/care about this?  You aren't telling

> them what device was deferred, and you don't need to as the bus itself

> already knows this information as it did the deferring!

>

> confused,


This notifier is just to let others that the deferred probe has happened and
it is a good time to retry operation, which earlier failed due to missing
resources (i.e. power domains, clocks). Such case is with registering AMBA
device (not the driver!). During AMBA device registration, bus code has 
to read
some device's registers to get its device CID/PID. To do this, device's 
clocks
and power domain has to be turned on. Those however might not be available
that time. With this notifier, AMBA bus code is able to retry device
registration, which earlier failed due to missing clocks or power domain.

This CID/PID reading has to be done during device registration time because
of the already deployed userspace ABI. CID/PID values are reported to
userspace, which might rely on them to load proper driver modules.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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diff mbox

Patch

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 16688f50729c..208466eb83fb 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -19,6 +19,7 @@ 
 
 #include <linux/device.h>
 #include <linux/delay.h>
+#include <linux/notifier.h>
 #include <linux/module.h>
 #include <linux/kthread.h>
 #include <linux/wait.h>
@@ -53,6 +54,7 @@  static LIST_HEAD(deferred_probe_pending_list);
 static LIST_HEAD(deferred_probe_active_list);
 static struct workqueue_struct *deferred_wq;
 static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
+static BLOCKING_NOTIFIER_HEAD(deferred_notifier_head);
 
 /*
  * In some cases, like suspend to RAM or hibernation, It might be reasonable
@@ -113,6 +115,9 @@  static void deferred_probe_work_func(struct work_struct *work)
 		put_device(dev);
 	}
 	mutex_unlock(&deferred_probe_mutex);
+
+	/* Notify any listeners about triggering deferred probe */
+	blocking_notifier_call_chain(&deferred_notifier_head, 0, NULL);
 }
 static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
 
@@ -224,6 +229,32 @@  static int deferred_probe_initcall(void)
 late_initcall(deferred_probe_initcall);
 
 /**
+ * deferred_probe_register_notifier - Register a notifier for deferred probe
+ * @nb: notifier block to signal
+ *
+ * This function allows caller to get a notification when deferred probe has
+ * been triggered. This lets it to retry some actions, which earlier failed
+ * with -EPROBE_DEFER error code.
+ */
+int deferred_probe_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&deferred_notifier_head, nb);
+}
+EXPORT_SYMBOL_GPL(deferred_probe_register_notifier);
+
+/**
+ * deferred_probe_unregister_notifier - Unregister a notifier
+ * @nb: notifier block to signal
+ *
+ * Unregister a previously registered deferred probe notifier.
+ */
+int deferred_probe_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&deferred_notifier_head, nb);
+}
+EXPORT_SYMBOL_GPL(deferred_probe_unregister_notifier);
+
+/**
  * device_is_bound() - Check if device is bound to a driver
  * @dev: device to check
  *
diff --git a/include/linux/device.h b/include/linux/device.h
index 002c59728dbe..c6496d1db5de 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1066,6 +1066,9 @@  extern int __must_check device_reprobe(struct device *dev);
 
 extern bool device_is_bound(struct device *dev);
 
+extern int deferred_probe_register_notifier(struct notifier_block *nb);
+extern int deferred_probe_unregister_notifier(struct notifier_block *nb);
+
 /*
  * Easy functions for dynamically creating devices on the fly
  */