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

ZhenHua
2013-04-26T01:11:51Z

On 04/25/2013 10:54 PM, Alan Stern wrote:
> On Thu, 25 Apr 2013, ZhenHua wrote:
>
>>>>> +#define UHCI_SUSPENDRH_RETRY_MAX 10
>>>>> +#define UHCI_SUSPENDRH_RETRY_DELAY 100
>>> 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.
> entirely.
>
>>> 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;
>>> spin_unlock_irq(&uhci->lock);
>>> msleep(1);
>>> spin_lock_irq(&uhci->lock);
>>> if (uhci->dead)
>>> return;
>>> }
>>>
>>> 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))
>
> to
>
> else if (time_after_eq(jiffies, uhci->auto_stop_time) &&
> !uhci->no_auto_stops)
>
> 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.

Thanks
Zhen-Hua