Date:   Wed, 1 Jan 2020 14:09:35 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        stable@...r.kernel.org
Subject: Re: [PATCH] usb: chipidea: host: Disable port power only if
 previously enabled

On 12/29/19 8:40 AM, Alan Stern wrote:
> On Sun, 29 Dec 2019, Guenter Roeck wrote:
> 
>> On Sat, Dec 28, 2019 at 02:33:01PM -0500, Alan Stern wrote:
>>>
>>> Let's try a slightly different approach.  What happens with this patch?
>>>
>>> Alan Stern
>>>
>>>
>>> Index: usb-devel/drivers/usb/core/hub.c
>>> ===================================================================
>>> --- usb-devel.orig/drivers/usb/core/hub.c
>>> +++ usb-devel/drivers/usb/core/hub.c
>>> @@ -1065,6 +1065,7 @@ static void hub_activate(struct usb_hub
>>>   		if (type == HUB_INIT) {
>>>   			delay = hub_power_on_good_delay(hub);
>>>   
>>> +			hub->power_bits[0] = ~0UL;	/* All ports on */
>>>   			hub_power_on(hub, false);
>>>   			INIT_DELAYED_WORK(&hub->init_work, hub_init_func2);
>>>   			queue_delayed_work(system_power_efficient_wq,
>>>
>>
>> That doesn't make a difference - the traceback is still seen with this patch
>> applied.
> 
> Can you trace what's going on?  Does this code pathway now end up
> calling ehci_port_power() for each root-hub port, and from there down
> into the chipidea driver?  If not, can you find where it gets
> sidetracked?
> 

A complete traceback is attached below, so, yes, I think it is safe to say that
ehci_port_power() is called unconditionally for each root-hub port on shutdown.

The only mystery to me was why ehci_port_power() isn't called to enable port power
when the port comes up. As it turns out, HCS_PPC(ehci->hcs_params) is false on my
simulated hardware, and thus ehci_port_power(..., true) is not called from
ehci_hub_control().

Given that, it may well be that the problem is not seen on "real" hardware,
at least not with real mcimx7d-sabre hardware, if the hub on that hardware does
support power control. To test this idea, I modified qemu to claim hub power
control support by setting the "power control support" capability bit. With
that, the traceback is gone.

Any suggestion how to proceed ?

Thanks,
Guenter

---
[   31.916567] ------------[ cut here ]------------
[   31.917178] WARNING: CPU: 0 PID: 182 at drivers/regulator/core.c:2598 _regulator_disable+0x1a8/0x210
[   31.917331] unbalanced disables for usb_otg2_vbus
[   31.917468] Modules linked in:
[   31.917877] CPU: 0 PID: 182 Comm: init Not tainted 5.4.8-rc1-00003-gb8e36d27e314 #1
[   31.918032] Hardware name: Freescale i.MX7 Dual (Device Tree)
[   31.918246] [<c0313658>] (unwind_backtrace) from [<c030d698>] (show_stack+0x10/0x14)
[   31.918397] [<c030d698>] (show_stack) from [<c113439c>] (dump_stack+0xe0/0x10c)
[   31.918522] [<c113439c>] (dump_stack) from [<c0349098>] (__warn+0xf4/0x10c)
[   31.918641] [<c0349098>] (__warn) from [<c0349128>] (warn_slowpath_fmt+0x78/0xbc)
[   31.918768] [<c0349128>] (warn_slowpath_fmt) from [<c09f3c3c>] (_regulator_disable+0x1a8/0x210)
[   31.918900] [<c09f3c3c>] (_regulator_disable) from [<c09f3cdc>] (regulator_disable+0x38/0xe8)
[   31.919032] [<c09f3cdc>] (regulator_disable) from [<c0df837c>] (ehci_ci_portpower+0x38/0xdc)
	ehci_ci_portpower() calls regulator_enable() or regulator_disable()
	if priv->reg_vbus is not NULL
[   31.919166] [<c0df837c>] (ehci_ci_portpower) from [<c0db5724>] (ehci_port_power+0x50/0xa4)
	ehci_port_power() calls hcd->driver->port_power(), which is ehci_ci_portpower()
[   31.919296] [<c0db5724>] (ehci_port_power) from [<c0db5ba0>] (ehci_silence_controller+0x5c/0xc4)
	ehci_silence_controller() calls ehci_turn_off_all_ports(), which calls
	ehci_port_power() for each port
[   31.919430] [<c0db5ba0>] (ehci_silence_controller) from [<c0db7dc4>] (ehci_stop+0x3c/0xcc)
	ehci_silence_controller() called unconditionally from ehci_stop()
[   31.919560] [<c0db7dc4>] (ehci_stop) from [<c0d5c504>] (usb_remove_hcd+0xe0/0x19c)	
	ehci_stop() called unconditionally from usb_remove_hcd() with hcd->driver->stop(hcd);
[   31.919685] [<c0d5c504>] (usb_remove_hcd) from [<c0df7e08>] (host_stop+0x38/0xa8)
[   31.919809] [<c0df7e08>] (host_stop) from [<c0df3704>] (ci_hdrc_remove+0x44/0xe4)
[   31.919932] [<c0df3704>] (ci_hdrc_remove) from [<c0b1a5e4>] (platform_drv_remove+0x20/0x40)
[   31.920062] [<c0b1a5e4>] (platform_drv_remove) from [<c0b18a50>] (device_release_driver_internal+0xe8/0x1b8)
[   31.920210] [<c0b18a50>] (device_release_driver_internal) from [<c0b17464>] (bus_remove_device+0xd0/0xfc)
[   31.920351] [<c0b17464>] (bus_remove_device) from [<c0b1401c>] (device_del+0x140/0x374)
[   31.920477] [<c0b1401c>] (device_del) from [<c0b1aaf8>] (platform_device_del.part.3+0x10/0x74)
[   31.920608] [<c0b1aaf8>] (platform_device_del.part.3) from [<c0b1ab8c>] (platform_device_unregister+0x1c/0x28)
[   31.920758] [<c0b1ab8c>] (platform_device_unregister) from [<c0df22f4>] (ci_hdrc_remove_device+0xc/0x20)
[   31.920898] [<c0df22f4>] (ci_hdrc_remove_device) from [<c0df9ea4>] (ci_hdrc_imx_remove+0x28/0x110)
[   31.921033] [<c0df9ea4>] (ci_hdrc_imx_remove) from [<c0b15ac4>] (device_shutdown+0x180/0x224)
[   31.921166] [<c0b15ac4>] (device_shutdown) from [<c037652c>] (kernel_restart+0xc/0x50)
[   31.921292] [<c037652c>] (kernel_restart) from [<c03767d0>] (__do_sys_reboot+0x15c/0x1ec)
[   31.921444] [<c03767d0>] (__do_sys_reboot) from [<c0301000>] (ret_fast_syscall+0x0/0x28)
[   31.921595] Exception stack(0xc93c1fa8 to 0xc93c1ff0)

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