Re: [PATCH v2] USB: Disable USB2 LPM at shutdown

[Kai-Heng Feng]

Hi Greg,

at 17:22, Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx> wrote:

> at 22:17, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> > I agree with Kai-Heng, this seems like a fairly light-weight solution
> > to a reasonable problem.
>
> Thanks for your review.
>
> > As to the issue of how much it will slow down system shutdowns, I have
> > no idea.  Probably not very much, unless somebody has an unusually
> > large number of USB devices plugged in, but only testing can give a
> > real answer.
>
> In addition to that, only USB2 devices that enable LPM will slow down  
> shutdown process.
> Right now only internally connected USB2 devices enable LPM, so the  
> numbers are even lower.
>
> > I suppose we could add an HCD flag for host controllers which require
> > this workaround.  Either way, it's probably not a very big deal.
>
> IMO this is not necessary. Only xHCI that reports hw_lpm_support will be  
> affected. At least for PC, this only became true after Whiskey Lake.
>
> Kai-Heng
>
> > Alan Stern

This patch is included in Ubuntuâs kernel for a while now, and thereâs no  
regression report so far.
Please consider merge this patch.

Kai-Heng