Re: [RFC PATCH 0/1] hibernate and roothub port power

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 9.6.2022 18.08, Evan Green wrote:
> On Thu, Jun 9, 2022 at 12:58 AM Mathias Nyman
> <mathias.nyman@linux.intel.com> wrote:
>>
>> On 8.6.2022 16.43, Alan Stern wrote:
>>> On Wed, Jun 08, 2022 at 02:47:22PM +0300, Mathias Nyman wrote:
>>>> On 8.6.2022 11.19, Oliver Neukum wrote:
>>>>>
>>>>>
>>>>> On 07.06.22 15:58, Mathias Nyman wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>>> In shutdown (S5), with xHCI as host, this can be solved fairly easily
>>>>>> by turning off roothub port power in the .shutdown path.
>>>>>
>>>>> That would suck for the people who charge their phone from their
>>>>> computer.
>>>>
>>>> Good point.
>>>> My guess is that xHC port power bits won't actually turn off VBus for those
>>>> Sleep-and-charge, or Always-on ports.
>>>> VBus is allowed to be on even if port is in power-off state, but usb link state
>>>> should be forced to ss.Disabled from other states, like U3.
>>>>
>>>> Need to try it out, it's possible this turns off VBus for some usb-A ports
>>>> on some older systems that earlier (accidentally?) supplied VBus on
>>>> "normal" ports after shutdown.
>>>
>>> How about turning off port power _only_ in the shutdown or unbind path,
>>> and setting the port link states to ss.Disabled in the poweroff or
>>> poweroff_noirq stage of hibernation (if wakeup is disabled)?  Would that
>>> solve the problem of the firmware needing to time out on reboot?
>>>
>>
>> That would be optimal, but unfortunately xHCI doesn't support setting link
>> state directly to ss.Disabled. Only way is to clear port power (PP) bit.
>>
>> To avoid turning off VBus in hibernate we could limit port power bit clearing
>> to xHC hosts that don't have the Port Power Control (PPC) capability flag.
>>
>> We know these xHC hosts don't control power switches, and clearing PP won't turn
>> off VBus (xhci 5.4.8, PORTRSC)
>>
>> This could be a solution for some hosts, but probably not cover all.
>> Not sure if the hardware this was reported on has PPC flag set.
> 
> It appears it does not, HCCPARAMS1 for both USB controllers seems to
> be 0x20007fc1 (missing bit 3). You can check my work in case I made an
> error here: https://pastebin.com/9raZc63N
> -Evan

Thanks, good to know.
So if disabling ports in hibernate doesn't work then we could turn off port power for
hosts with PPC==0. It should at least solve the issue for this particular system,
and not change current VBus policy in hibernate.

-Mathias