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

From: rishabhb
Date: Fri Sep 07 2018 - 16:34:34 EST


On 2018-08-13 10:39, Rishabh Bhatnagar wrote:
From: Rishabh Bhatnagar <rishabhb@xxxxxxxxxxxxxx>

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.
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.

Signed-off-by: Vikram Mulukutla <markivx@xxxxxxxxxxxxxx>
Signed-off-by: Rishabh Bhatnagar <rishabhb@xxxxxxxxxxxxxx>
---

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

Hi Rafael
Just a reminder about this patch. Let me know if you want me to add/edit anything else.
-Rishabh