linux-kernel - Re: [PATCH v4] USB: Don't enable LPM if it's already enabled

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Date:   Wed, 9 Jan 2019 00:04:08 +0800
From:   Kai Heng Feng <kai.heng.feng@...onical.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] USB: Don't enable LPM if it's already enabled



> On Jan 8, 2019, at 11:41 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> 
> On Mon, Dec 03, 2018 at 06:26:43PM +0800, Kai-Heng Feng wrote:
>> USB Bluetooth controller QCA ROME (0cf3:e007) sometimes stops working
>> after S3:
>> [ 165.110742] Bluetooth: hci0: using NVM file: qca/nvm_usb_00000302.bin
>> [ 168.432065] Bluetooth: hci0: Failed to send body at 4 of 1953 (-110)
>> 
>> After some experiments, I found that disabling LPM can workaround the
>> issue.
>> 
>> On some platforms, the USB power is cut during S3, so the driver uses
>> reset-resume to resume the device. During port resume, LPM gets enabled
>> twice, by usb_reset_and_verify_device() and usb_port_resume().
>> 
>> So let's enable LPM for just once, as this solves the issue for the
>> device in question.
>> 
>> Also consolidate USB2 LPM functions to usb_enable_usb2_hardware_lpm()
>> and usb_disable_usb2_hardware_lpm().
> 
> I thought I asked for this to be two different patches.  One that does
> the "consolidation", and then one that fixes the bug.  You are mixing
> two different things here together, making it harder to review.
> 
> Can you please break this up and send a patch series, with the correct
> "Fixes:" tag added to the second patch that actually fixes the issue?

The consolidation itself is the fix, so I am not sure how to break this up.

In reset-resume case, LPM gets enabled twice, by
usb_reset_and_verify_device() and usb_port_resume().

If it’s a normal resume, LPM only gets enabled once, by
usb_port_resume().

Since all three checks (capable, allowed and enabled) are merged to
a single place, enabling LPM twice can be avoided, hence fixing the
issue.

Kai-Heng

> 
> thanks,
> 
> greg k-h