Re [patch 2/3] fastboot: turn the USB hostcontroller initcalls into async initcalls

Re [patch 2/3] fastboot: turn the USB hostcontroller initcalls into async initcalls

[Alan Stern]

On 18 July, 2008, Arjan van de Ven wrote:

> From: Arjan van de Ven <arjan@linux.intel.com>
> Subject: [PATCH] fastboot: turn the USB hostcontroller initcalls into 
> async initcalls
> 
> the USB host controller init calls take a long time, mostly due to a
> "minimally 100 msec" delay *per port* during initialization.
> These are prime candidates for going in parallel to everything else.
> 
> The USB device ordering is not affected by this due to the
> serialized-within-eachother property of async initcalls.

Is there some reason this patch wasn't posted to the linux-usb mailing
list as well as to LKML?

Where is this "minimally 100 msec" per-port delay you refer to?  
Offhand I can't recall any such delays in the init routines.

Alan Stern

Re: Re [patch 2/3] fastboot: turn the USB hostcontroller initcalls into async initcalls

[Simon Arlott]

On 19/07/08 16:25, Alan Stern wrote:
> On 18 July, 2008, Arjan van de Ven wrote:
> 
>> From: Arjan van de Ven <arjan@linux.intel.com>
>> Subject: [PATCH] fastboot: turn the USB hostcontroller initcalls into 
>> async initcalls
>> 
>> the USB host controller init calls take a long time, mostly due to a
>> "minimally 100 msec" delay *per port* during initialization.
>> These are prime candidates for going in parallel to everything else.
>> 
>> The USB device ordering is not affected by this due to the
>> serialized-within-eachother property of async initcalls.
> 
> Is there some reason this patch wasn't posted to the linux-usb mailing
> list as well as to LKML?
> 
> Where is this "minimally 100 msec" per-port delay you refer to?  
> Offhand I can't recall any such delays in the init routines.
> 

usb/core/hub.c:

/* USB 2.0 spec, 7.1.7.3 / fig 7-29:
 *
 * Between connect detection and reset signaling there must be a delay
 * of 100ms at least for debounce and power-settling.  The corresponding
 * timer shall restart whenever the downstream port detects a disconnect.
 *
 * Apparently there are some bluetooth and irda-dongles and a number of
 * low-speed devices for which this debounce period may last over a second.
 * Not covered by the spec - but easy to deal with.
 *
 * This implementation uses a 1500ms total debounce timeout; if the
 * connection isn't stable by then it returns -ETIMEDOUT.  It checks
 * every 25ms for transient disconnects.  When the port status has been
 * unchanged for 100ms it returns the port status.
 */

Could it do that for all ports on the hub in parallel instead?

-- 
Simon Arlott

Re: Re [patch 2/3] fastboot: turn the USB hostcontroller initcalls into async initcalls

[Arjan van de Ven]

On Sat, 19 Jul 2008 11:25:29 -0400 (EDT)
Alan Stern <stern@rowland.harvard.edu> wrote:

> On 18 July, 2008, Arjan van de Ven wrote:
> 
> > From: Arjan van de Ven <arjan@linux.intel.com>
> > Subject: [PATCH] fastboot: turn the USB hostcontroller initcalls
> > into async initcalls
> > 
> > the USB host controller init calls take a long time, mostly due to a
> > "minimally 100 msec" delay *per port* during initialization.
> > These are prime candidates for going in parallel to everything else.
> > 
> > The USB device ordering is not affected by this due to the
> > serialized-within-eachother property of async initcalls.
> 
> 
> Where is this "minimally 100 msec" per-port delay you refer to?  
> Offhand I can't recall any such delays in the init routines.
> 

it's here (in drivers/usb/core/hub.c::hub_power_on):

                                "non-switchable hub\n");
        for (port1 = 1; port1 <= hub->descriptor->bNbrPorts; port1++)
                set_port_feature(hub->hdev, port1, USB_PORT_FEAT_POWER);

        /* Wait at least 100 msec for power to become stable */
        msleep(max(pgood_delay, (unsigned) 100));
}

at least my eeepc901 hits that like 6 or 7 times
(because if I shorten the 100 the boot goes a ton faster.. but that's
obviously just a bad hack)
-- 
If you want to reach me at my work email, use arjan@linux.intel.com
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org

Re: Re [patch 2/3] fastboot: turn the USB hostcontroller initcalls into async initcalls

[Alan Stern]

On Sat, 19 Jul 2008, Arjan van de Ven wrote:

> On Sat, 19 Jul 2008 11:25:29 -0400 (EDT)
> Alan Stern <stern@rowland.harvard.edu> wrote:
> 
> > On 18 July, 2008, Arjan van de Ven wrote:
> > 
> > > From: Arjan van de Ven <arjan@linux.intel.com>
> > > Subject: [PATCH] fastboot: turn the USB hostcontroller initcalls
> > > into async initcalls
> > > 
> > > the USB host controller init calls take a long time, mostly due to a
> > > "minimally 100 msec" delay *per port* during initialization.
> > > These are prime candidates for going in parallel to everything else.
> > > 
> > > The USB device ordering is not affected by this due to the
> > > serialized-within-eachother property of async initcalls.
> > 
> > 
> > Where is this "minimally 100 msec" per-port delay you refer to?  
> > Offhand I can't recall any such delays in the init routines.
> > 
> 
> it's here (in drivers/usb/core/hub.c::hub_power_on):
> 
>                                 "non-switchable hub\n");
>         for (port1 = 1; port1 <= hub->descriptor->bNbrPorts; port1++)
>                 set_port_feature(hub->hdev, port1, USB_PORT_FEAT_POWER);
> 
>         /* Wait at least 100 msec for power to become stable */
>         msleep(max(pgood_delay, (unsigned) 100));
> }
> 
> at least my eeepc901 hits that like 6 or 7 times
> (because if I shorten the 100 the boot goes a ton faster.. but that's
> obviously just a bad hack)

That isn't a *per-port* delay.  It's a single delay used concurrently
for all the ports in the root hub; the msleep call occurs outside the 
"for" loop.

Maybe you meant 100 ms *per controller*.  I agree, it's best for these 
delays to occur in parallel.  Now if only we could do the same with 
suspend and resume...

Alan Stern

Re: Re [patch 2/3] fastboot: turn the USB hostcontroller initcalls into async initcalls

[Alan Stern]

On Sat, 19 Jul 2008, Simon Arlott wrote:

> usb/core/hub.c:
> 
> /* USB 2.0 spec, 7.1.7.3 / fig 7-29:
>  *
>  * Between connect detection and reset signaling there must be a delay
>  * of 100ms at least for debounce and power-settling.  The corresponding
>  * timer shall restart whenever the downstream port detects a disconnect.
>  *
>  * Apparently there are some bluetooth and irda-dongles and a number of
>  * low-speed devices for which this debounce period may last over a second.
>  * Not covered by the spec - but easy to deal with.
>  *
>  * This implementation uses a 1500ms total debounce timeout; if the
>  * connection isn't stable by then it returns -ETIMEDOUT.  It checks
>  * every 25ms for transient disconnects.  When the port status has been
>  * unchanged for 100ms it returns the port status.
>  */
> 
> Could it do that for all ports on the hub in parallel instead?

In fact it will, to a large extent.  The new code isn't present in
2.6.26 but it ought to be in 2.6.27-rc1.

However Arjan wasn't talking about debounce delays; he was talking 
about port-power-on delays.  A nice improvement would be to combine the 
two types of delay into one.  I'll look into it...

Alan Stern