[PATCH v1] dd: Invoke one probe retry cycle after some initcall levels

[Rishabh Bhatnagar <rishabhb@codeaurora.org>]

Drivers that are registered at an initcall level may have to
wait until late_init before the probe deferral mechanism can
retry their probe functions. It is possible that their
dependencies were resolved much earlier, in some cases even
before the next initcall level. Invoke one probe retry cycle
at every _sync initcall level after subsys initcall, allowing
these drivers to be probed earlier.

Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
---

To give an example many Qualcomm drivers are dependent on the regulator and 
bus driver. Both the regulator and bus driver are probed in the 
subsys_initcall level. Now the probe of bus driver requires regulator to be 
working. If the probe of bus driver happens before regulator, then bus 
driver's probe will be deferred and all other device's probes which depend 
on bus driver will also be deferred. 
The impact of this problem is reduced if we have this patch.

Changes since v0:
* Remove arch_initcall_sync(deferred_probe_initcall) from patch. This is not
  really needed as none of the devices are re-probed in arch_initcall_sync
  level.

 drivers/base/dd.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 1435d72..9aa41aa 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -224,23 +224,43 @@ void device_unblock_probing(void)
 	driver_deferred_probe_trigger();
 }
 
+static void enable_trigger_defer_cycle(void)
+{
+	driver_deferred_probe_enable = true;
+	driver_deferred_probe_trigger();
+	/*
+	 * Sort as many dependencies as possible before the next initcall
+	 * level
+	 */
+	flush_work(&deferred_probe_work);
+}
+
 /**
  * deferred_probe_initcall() - Enable probing of deferred devices
  *
  * We don't want to get in the way when the bulk of drivers are getting probed.
  * Instead, this initcall makes sure that deferred probing is delayed until
- * late_initcall time.
+ * all the registered initcall functions at a particular level are completed.
+ * This function is invoked at every *_initcall_sync level.
  */
 static int deferred_probe_initcall(void)
 {
-	driver_deferred_probe_enable = true;
-	driver_deferred_probe_trigger();
-	/* Sort as many dependencies as possible before exiting initcalls */
-	flush_work(&deferred_probe_work);
+	enable_trigger_defer_cycle();
+	driver_deferred_probe_enable = false;
+	return 0;
+}
+subsys_initcall_sync(deferred_probe_initcall);
+fs_initcall_sync(deferred_probe_initcall);
+device_initcall_sync(deferred_probe_initcall);
+
+static int deferred_probe_enable_fn(void)
+{
+	/* Enable deferred probing for all time */
+	enable_trigger_defer_cycle();
 	initcalls_done = true;
 	return 0;
 }
-late_initcall(deferred_probe_initcall);
+late_initcall(deferred_probe_enable_fn);
 
 /**
  * device_is_bound() - Check if device is bound to a driver
-- 
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