Subject: [PATCH] amba: Retry adding deferred devices at late_initcall

From: Rob Herring <[email-masked]>
Date: Mon, 27 Apr 2020 16:25:14 -0500

If amba bus devices defer when adding, the amba bus code simply retries
adding the devices every 5 seconds. This doesn't work well as it
completely unsynchronized with starting the init process which can
happen in less than 5 secs. Add a retry during late_initcall. If the
amba devices are added, then deferred probe takes over. If the
dependencies have not probed at this point, then there's no improvement
over previous behavior. To completely solve this, we'd need to retry
after every successful probe as deferred probe does.

The list_empty() check now happens outside the mutex, but the mutex
wasn't necessary in the first place.

This needed to use deferred probe instead of fragile initcall ordering
on 32-bit VExpress systems where the apb_pclk has a number of probe
dependencies (vexpress-sysregs, vexpress-config).

Cc: John Stultz <[email-masked]>
Cc: Saravana Kannan <[email-masked]>
Cc: Linus Walleij <[email-masked]>
Cc: Sudeep Holla <[email-masked]>
Cc: Nicolas Saenz Julienne <[email-masked]>
Cc: Geert Uytterhoeven <[email-masked]>
Cc: Russell King <[email-masked]>
Signed-off-by: Rob Herring <[email-masked]>
---
 drivers/amba/bus.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index fe1523664816..e797995fc65b 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -505,7 +505,7 @@ static DECLARE_DELAYED_WORK(deferred_retry_work, amba_deferred_retry_func);
 
 #define DEFERRED_DEVICE_TIMEOUT (msecs_to_jiffies(5 * 1000))
 
-static void amba_deferred_retry_func(struct work_struct *dummy)
+static int amba_deferred_retry(void)
 {
 	struct deferred_device *ddev, *tmp;
 
@@ -521,11 +521,19 @@ static void amba_deferred_retry_func(struct work_struct *dummy)
 		kfree(ddev);
 	}
 
+	mutex_unlock(&deferred_devices_lock);
+
+	return 0;
+}
+late_initcall(amba_deferred_retry);
+
+static void amba_deferred_retry_func(struct work_struct *dummy)
+{
+	amba_deferred_retry();
+
 	if (!list_empty(&deferred_devices))
 		schedule_delayed_work(&deferred_retry_work,
 				      DEFERRED_DEVICE_TIMEOUT);
-
-	mutex_unlock(&deferred_devices_lock);
 }
 
 /**
-- 
2.20.1

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