Re: [PATCH 1/1] driver,usb: Fix a warning in uhci-hcd driver

From: ZhenHua
Date: Thu Apr 25 2013 - 21:11:54 EST

On 04/25/2013 10:54 PM, Alan Stern wrote:
On Thu, 25 Apr 2013, ZhenHua wrote:

Why is the delay set to 100 us? Isn't that excessively large? How
long does it take for this controller to go into suspend?
This controller will take about 200~400 us, but I am not sure how long
other devices will take.
I set interval to 100 us, so it will save more time.
A 400-us delay is fairly long. It would be better to avoid it
The device needs about 200~400 us to get stopped, not OS.
For other devices, it will not wait.

Why are these variables u16? Why not int?
uhci_readw will return u16.
That's not a good reason, since u16 fits perfectly well inside an
int. But never mind...

Anyway, a better approach would be not to add a delay loop at all.
Instead, change this test:

if (!auto_stop && !(uhci_readw(uhci, USBSTS) & USBSTS_HCH)) {
uhci->rh_state = UHCI_RH_SUSPENDING;
if (uhci->dead)

When the iLo controller is present, make the "if" statement always
succeed. Then you'll get a whole 1-ms delay.
This will cause more operation and more time for other devices.
Actually what I wrote was wrong anyway. I forgot that when auto_stop
is set, the routine is not allowed to sleep.

A better way to solve your problem is to change uhci_hub_status_data().
In the UHCI_RH_RUNNING_NODEVS case, change the line that says

else if (time_after_eq(jiffies, uhci->auto_stop_time))


else if (time_after_eq(jiffies, uhci->auto_stop_time) &&

where uhci->no_auto_stops is a new bitflag that you set inside
uhci_pci_init() if you detect that the controller is an iLo virtual
UHCI controller.

This way there will always be a 1-ms delay, so the slow controller will
suspend successfully. And other types of host controllers won't be
affected, because the no_auto_stops flag won't get set for them.

Alan Stern

I think it is a good idea, and the logic of the code may be more clear. I will do some test on my system.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at