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Subject: Re: [PATCH v2] USB: Disable USB2 LPM at shutdown
From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
In-Reply-To: <46147522-7BC2-4C30-B3E5-6568E9642982@canonical.com>
Date:   Mon, 5 Aug 2019 20:58:33 +0800
Cc:     Alan Stern <stern@rowland.harvard.edu>,
        Mathias Nyman <mathias.nyman@linux.intel.com>,
        Linux USB List <linux-usb@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
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Message-Id: <27A5C1CC-E0A4-4CAF-B81E-90EE76C8A887@canonical.com>
References: <Pine.LNX.4.44L0.1906061013490.1641-100000@iolanthe.rowland.org>
 <46147522-7BC2-4C30-B3E5-6568E9642982@canonical.com>
To:     Greg KH <gregkh@linuxfoundation.org>
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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