Date:   Sun, 25 Aug 2019 00:22:51 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     jikos@...nel.org, benjamin.tissoires@...hat.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] HID: quirks: Disable runtime suspend on Microsoft Corp.
 Basic Optical Mouse v2.0

at 21:37, Oliver Neukum <oneukum@...e.com> wrote:

> Am Donnerstag, den 22.08.2019, 21:23 +0800 schrieb Kai-Heng Feng:
>> at 18:38, Oliver Neukum <oneukum@...e.com> wrote:
>>> Well, sort of. The USB spec merely states how to enter and exit
>>> a suspended state and that device state must not be lost.
>>> It does not tell you what a suspended device must be able to do.
>>
>> But shouldn’t remote wakeup signaling wakes the device up and let it exit
>> suspend state?
>
> Yes. Have you tested using a button? If they indeed do not work, then
> the device lies about supporting remote wakeup. That would warrant a
> quirk, but for remote wakeup.

Button click can wake the mouse up but not movement.

>
>> Or it’s okay to let the device be suspended when remote wakeup is needed
>> but broken?
>
> Again, the HID spec does not specify what should trigger a remote
> wakeup. Limiting this to mouse buttons but not movements is
> inconvinient, but not buggy.

Ok, I still find the behavior really surprising.

>
> This is indeed what Windows does. The device is suspended when the
> screen saver switches on. That we do not do that is a deficiency
> of X.
> To use runtime PM regularly you need an .ini file

Thanks for the explanation. I guess we can mimic the behavior in systemd or  
upower.

>
>
>>> In other words, if on your system it is on, you need to look
>>> at udev, not the kernel.
>>
>> So if a device is broken when “power/control” is flipped by user, we  
>> should
>> deal it at userspace? That doesn’t sound right to me.
>
> If it is broken, as in crashing we could talk about it. If it merely
> does not do what you want, then, yes, that is for user space to deal
> with.

Ok, I’ll take a look at userspace then.

>
>>> Well, no. Runtime PM is a trade off. You lose something if you use
>>> it. If it worked just as well as full power, you would never use
>>> full power, would you?
>>
>> I am not asking the suspended state to work as full power, but to  
>> prevent a
>> device enters suspend state because of broken remote wakeup.
>
> What then would be the difference between suspended and active? A small
> delay in data transfer?

Non-operational but with wakeup capability and vise versa.

>
>>> Whether the loss of functionality or performance is worth the energy
>>> savings is a policy decision. Hence it belongs into udev.
>>> Ideally the kernel would tell user space what will work in a
>>> suspended state. Unfortunately HID does not provide support for that.
>>
>> I really don’t think “loss of functionally” belongs to policy decision.  
>> But
>> that’s just my opinion.
>
> That is just what we do if, for example, you choose between the configs
> of a USB device or when you use authorization.
>
>> Maybe just calling usb_autopm_put_interface() in usbhid_close() to balance
>> the refcount?
>
> No, the refcount is good. If remote wakeup is totally broken, you need
> to introduce a quirk that will prevent the kernel from believing the
> device when it claims to support it.

Ok. I’ll see if it’s possible to mimic other OS under current Linux Desktop.

Kai-Heng

>
> 	Regards
> 		Oliver

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