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

Kai-Heng Feng
2019-08-05T12:58:43Z

Hi Greg,

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

> at 22:17, Alan Stern <stern@rowland.harvard.edu> 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 Ubuntu’s kernel for a while now, and there’s no
regression report so far.
Please consider merge this patch.

Kai-Heng