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

[Kai Heng Feng <kai.heng.feng@canonical.com>]

> On Jan 8, 2019, at 00:16, Greg KH <gregkh@linuxfoundation.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().
>> 
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> 
> What kernel patch does this one "fix"?  Adding a "Fixes:" tag would be
> good to try to figure out how far back in the kernel releases this
> should be backported.

Fixes: de68bab4fa96 ("usb: Don't enable USB 2.0 Link PM by default.”)

The usb_set_usb2_hardware_lpm() was added to usb_reset_and_verify_device()
by this commit.

Kai-Heng

> 
> thanks,
> 
> greg k-h