linux-kernel - Re: [RFC PATCH 4/6] USB: ehci-omap: Suspend the controller during bus suspend

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Date:	Mon, 1 Jul 2013 11:16:45 +0300
From:	Roger Quadros <rogerq@...com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	<balbi@...com>, <tony@...mide.com>, <ruslan.bilovol@...com>,
	<linux-usb@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 4/6] USB: ehci-omap: Suspend the controller during
 bus suspend

On 06/28/2013 10:06 PM, Alan Stern wrote:
> On Fri, 28 Jun 2013, Roger Quadros wrote:
> 
>>> That's not what I meant.  Never mind the pinctrl; I was asking about
>>> the EHCI controller itself.  Under what circumstances does the
>>> controller assert its wakeup signal?  And how do you tell it to stop
>>> asserting that signal?
>>
>> I believe this would be through the EHCI Interrupt enable register (USBINTR).
>> I'm not aware of any other mechanism.
> 
> That's strange, because ehci_suspend() sets the intr_enable register to 
> 0.  So how do you ever get any wakeup interrupts at all?

Because after ehci_suspend() for OMAP, we solely rely on the out of band wake up
mechanism. i.e. Pad wakeup.
> 
>> Right. It seems the external hub has signaled remote wakeup but the kernel doesn't
>> resume the root hub's port it is connected to.
>>
>> By observing the detailed logs below you can see that the root hub does not generate
>> an INTerrupt transaction to notify the port status change event. I've captured the pstatus
>> and GetPortStatus info as well.
> 
> We don't need an interrupt.  The driver is supposed to detect the
> remote wakeup sent by the external hub all by itself.

OK. Then it could point to a bug in our stack.
> 
>> Failing case
>> ------------
>>
>> [   16.108032] usb usb1: usb auto-resume
>> [   16.108062] ehci-omap 48064800.ehci: resume root hub
>> [   16.108154] hub 1-0:1.0: hub_resume
>> [   16.108398] ehci_hub_control GetPortStatus, port 1 temp = 0x1000
>> [   16.108459] ehci_hub_control GetPortStatus, port 2 temp = 0x14c5
> 
> Here's where we should detect it.  Look at the GetPortStatus case in
> ehci_hub_control(); the PORT_RESUME bit (0x0040) is set in temp, so the
> "Remote Wakeup received?" code should run.  In particular, these lines
> should run:
> 
> 			/* resume signaling for 20 msec */
> 			ehci->reset_done[wIndex] = jiffies
> 					+ msecs_to_jiffies(20);
> 			usb_hcd_start_port_resume(&hcd->self, wIndex);
> 			/* check the port again */
> 			mod_timer(&ehci_to_hcd(ehci)->rh_timer,
> 					ehci->reset_done[wIndex]);
> 
> Therefore 20 ms later, around timestamp 16.128459,
> ehci_hub_status_data() should have been called.  At that time, the
> root-hub port should have been fully resumed.

OK. right.
> 
>> [   16.108551] hub 1-0:1.0: port 2: status 0507 change 0000
>> [   16.108612] ehci_hub_control GetPortStatus, port 3 temp = 0x1000
>> [   16.108642] hub 1-0:1.0: hub_activate submitting urb
>> [   16.109222] ehci_irq port 3 pstatus 0x1000
>> [   16.109222] ehci_irq port 2 pstatus 0x14c5
>> [   16.109252] ehci_irq port 1 pstatus 0x1000
>> [   16.109374] hub 1-0:1.0: state 7 ports 3 chg 0000 evt 0000
> 
> But apparently nothing happened.  Why not?  Did the rh_timer get reset?  
> Maybe you can find out what went wrong.
> 

Sure. I'll investigate.

> (Hmmm, we seem to be missing a
> 
> 			set_bit(wIndex, &ehci->resuming_ports);
> 
> line in there...)
> 
>>> Also, why do you need omap->initialized?  Do you think you might get a 
>>> wakeup interrupt before the controller has been fully set up?  I don't 
>>> see how you could, given the pm_runtime_get_sync() call in the probe 
>>> routine.
>>>
>>
>> During probe we need to runtime_resume the device before usb_add_hcd() since the
>> controller clocks must be enabled before any registers are accessed.
>> However, we cannot call ehci_resume() before usb_add_hcd(). So to prevent this
>> chicken & egg situation, I've used the omap->initialized flag. It only indicates that
>> the ehci structures are initialized and we can call ehci_resume/suspend().
> 
> Ah, yes.  Other subsystems, such as PCI, face exactly the same problem.
> 
> You probably shouldn't call it "initialized", though, because the same
> issue arises in ehci_hcd_omap_remove() -- the pm_runtime_put_sync()  
> there would end up calling ehci_suspend() after usb_remove_hcd().  
> "bound" or "started" would be better names.
> 
OK. Started seems fine.

cheers,
-roger
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