[U-Boot] [PATCH 4/6] usb: usb_hub_power_on(): Use 100ms power-on delay instead of 1 sec (optionally)

[Stefan Roese]

In a system with a complex USB infrastrcture (many USB hubs), the
power-on delay of mininimum 1 second for each USB hub results in a quite
big USB scanning time. Many USB devices can deal with much lower
power-on delays. In my test system, even 10ms seems to be enough
for the USB device to get detected correctly. This patch now
reduces the minimum 1 second delay to a minumum of 100ms instead.
This results in a big USB scan time reduction:

Here the numbers for my current board:

Without this patch:
starting USB...
USB0:   USB EHCI 1.00
scanning bus 0 for devices... 9 USB Device(s) found

time: 10.822 seconds

With this patch:
starting USB...
USB0:   USB EHCI 1.00
scanning bus 0 for devices... 9 USB Device(s) found

time: 6.319 seconds

So ~4.5 seconds of USB scanning time reduction.

I'm not really sure if this patch can be accepted in general as is.

In patch 0d437bca [usb: hub: fix power good delay timing] by Stephen
Warren, this delay was changes according to "Connect Timing ECN.pdf"
to a total of 1 second plus the hub port's power good time. Now its
changes back to 100ms which is a violation of this spec. But still,
for most USB devices this 100ms is more than enough. So its a valid
use-case to lower this time in special (perhaps static) USB
environments.

Signed-off-by: Stefan Roese <sr at denx.de>
Cc: Simon Glass <sjg at chromium.org>
Cc: Hans de Goede <hdegoede at redhat.com>
Cc: Stephen Warren <swarren at nvidia.com>
Cc: Marek Vasut <marex at denx.de>
---

 common/usb_hub.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/common/usb_hub.c b/common/usb_hub.c
index 780291f..d5fcd27 100644
--- a/common/usb_hub.c
+++ b/common/usb_hub.c
@@ -120,7 +120,11 @@ static void usb_hub_power_on(struct usb_hub_device *hub)
 		pgood_delay = max(pgood_delay,
 			          (unsigned)simple_strtol(env, NULL, 0));
 	debug("pgood_delay=%dms\n", pgood_delay);
+#if defined(CONFIG_USB_FAST_SCAN)
+	mdelay(pgood_delay + 100);
+#else
 	mdelay(pgood_delay + 1000);
+#endif
 }
 
 void usb_hub_reset(void)
-- 
2.7.2