[PATCH] usb-storage: Optimize scan delay more precisely

[Norihiko Hama]

Current storage scan delay is reduced by the following old commit.

a4a47bc03fe5 ("Lower USB storage settling delay to something more reasonable")

It means that delay is at least 'one second', or zero with delay_use=0.
'one second' is still long delay especially for embedded system but
when delay_use is set to 0 (no delay), error still observed on some USB drives.

So delay_use should not be set to 0 but 'one second' is quite long.

This patch optimizes scan delay more precisely
to minimize delay time but not to have any problems on USB drives
by adding module parameter 'delay_scale' of delay-time divisor.
By default, delay time is 'one second' for backward compatibility.
For example, it seems to be good by changing delay_scale=100,
that is 100 millisecond delay.

Signed-off-by: Norihiko Hama <Norihiko.Hama@xxxxxxxxxxxxxx>
---
 drivers/usb/storage/usb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
index 90aa9c12ffac..f4a755e364da 100644
--- a/drivers/usb/storage/usb.c
+++ b/drivers/usb/storage/usb.c
@@ -70,6 +70,9 @@ MODULE_LICENSE("GPL");
 static unsigned int delay_use = 1;
 module_param(delay_use, uint, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(delay_use, "seconds to delay before using a new device");
+static unsigned int delay_scale = MSEC_PER_SEC;
+module_param(delay_scale, uint, 0644);
+MODULE_PARM_DESC(delay_scale, "time scale of delay_use");
 
 static char quirks[128];
 module_param_string(quirks, quirks, sizeof(quirks), S_IRUGO | S_IWUSR);
@@ -1066,7 +1069,7 @@ int usb_stor_probe2(struct us_data *us)
 	if (delay_use > 0)
 		dev_dbg(dev, "waiting for device to settle before scanning\n");
 	queue_delayed_work(system_freezable_wq, &us->scan_dwork,
-			delay_use * HZ);
+			msecs_to_jiffies(delay_use * delay_scale));
 	return 0;
 
 	/* We come here if there are any problems */
-- 
2.17.1