Re: [PATCH 2/2] xhci: Improve the XHCI resume time

[Wesley Cheng <quic_wcheng@quicinc.com>]

Hi Mathias,

On 4/24/2023 8:05 AM, Mathias Nyman wrote:
> On 21.4.2023 7.58, Basavaraj Natikar wrote:
>>
>> On 4/20/2023 10:33 PM, Mark Hasemeyer wrote:
>>>> It may be necessary to wait only for auto-resume cases.
>>> I find this comment misleading as the patch assumes that it's only 
>>> necessary to
>>> wait for auto-resume cases. Are there any cases where the driver 
>>> should wait
>>> during system-resume?
>>
>> Only in case of auto-resume (runtime resume).
>>
>> Rewording the commit message as follows.
> 
> Thanks for fixing this extra system resume delay
> 
> Maybe some kind of big picture explanation could be added to the commit 
> message,
> such as:
> 
> Avoid extra 120ms delay during system resume.
> 
> xHC controller may signal wake up to 120ms before it shows which USB device
> caused the wake on the xHC port registers.
> 
> The xhci driver therefore checks for port activity up to 120ms during 
> resume,
> making sure that the hub driver can see the port change, and won't 
> immediately
> runtime suspend back due to no port activity.
> 
> This is however only needed for runtime resume as system resume will resume
> all child hubs and other child usb devices anyway.
> 
>>
>> Each XHCI controller while xhci_resumes by default takes 120 ms more if
>> there is no activity on the ports or no ports connected. Therefore, if
>> there are more USB controllers on the system, 120 ms more per controller
>> will add delay to system resume from suspended states like s2idle, S3 or
>> S4 states.
>>
>> Once the XHCI controller is in runtime suspended state (D3 state), on USB
>> device hotplug controller will runtime resume (D0 state) and check for
>> pending port events if no events, wait for 120 ms to re-check for port
>> activity to handle missed wake signal.
>>
>> A delay of 120 ms more to re-check for port activity is needed only in
>> auto-resume (runtime resume) cases. Hence, add a check only for runtime
>> resume from runtime suspend (D3->D0) to avoid the 120ms more delay for
>> other PM events (system resume from suspend states like s2idle, S3 or S4
>> states) so that the system resume time can be improved.
>>
>> Please let me know if any inputs.
> 
> I can only think of one minor side-effect that would be runtime 
> suspending back
> too early after system resume. This could happen when connecting the first
> usb device to a roothub on a (system) suspended setup?
> 
> steps:
> 1. in system suspend, no usb devices connected, xhci in D3, can signal 
> wake with PME#
> 2. connect first usb device, xHC signals PME# wake
> 3. system resumes, xhci resumes to D0, but no actity visible on xHC port 
> registers

Thanks for bringing up this topic Basavaraj.

Sorry for jumping into this thread, but was looking to optimize this 
resume timing as well, since it is affecting some of the host driven bus 
resume situations.  Just had a quick question about where the 120ms 
delay is required...

 From what I'm gathering from the USB3 spec, the 120ms timeout is the 
recommended time for tU3WakeupRetryDelay ("Table 7-12. LTSSM State 
Transition Timeouts").  This is the retry time that the device will wait 
before re-issuing another (potential) LFPS U3 wake.

My idea was to see if we could limit this delay only for when a SSUSB 
device is already connected to the root hub.  (ignore if HSUSB device 
connected)  We would be able to eliminate the delay for:
1.  No device connected to root hub
2.  Only HSUSB device connected

Is that a possibility we can add on top of what Basavaraj is adding?

Thanks
Wesley Cheng