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

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Message-ID: <Pine.LNX.4.44L0.1306281346430.1047-100000@iolanthe.rowland.org>
Date:	Fri, 28 Jun 2013 15:06:57 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roger Quadros <rogerq@...com>
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 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?

> 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.

> 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.

> [   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.

(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.

Alan Stern

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