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Date:   Thu, 11 Apr 2019 15:55:38 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] USB: Disable USB2 LPM at shutdown

at 18:22, Kai-Heng Feng <kai.heng.feng@...onical.com> wrote:

> at 00:01, Kai-Heng Feng <kai.heng.feng@...onical.com> wrote:
>
>>> On Jan 30, 2019, at 16:21, Greg KH <gregkh@...uxfoundation.org> wrote:
>>>
>>> On Thu, Jan 24, 2019 at 02:16:43PM +0800, Kai-Heng Feng wrote:
>>>> The QCA Rome USB Bluetooth controller has several issues once LPM gets
>>>> enabled:
>>>> - Fails to get enumerated in coldboot. [1]
>>>> - Drains more power (~ 0.2W) when the system is in S5. [2]
>>>> - Disappears after a warmboot. [2]
>>>>
>>>> The issue happens because the device lingers at LPM L1 in S5, so device
>>>> can't get enumerated even after a reboot.
>>>>
>>>> Disable LPM at shutdown to solve the issue.
>>>>
>>>> [1] https://bugs.launchpad.net/bugs/1757218
>>>> [2] https://patchwork.kernel.org/patch/10607097/
>>>>
>>>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>>>> ---
>>>> v2: Use new LPM helpers.
>>>>
>>>> drivers/usb/core/port.c | 9 +++++++++
>>>> 1 file changed, 9 insertions(+)
>>>>
>>>> diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
>>>> index 1a06a4b5fbb1..bbbb35fa639f 100644
>>>> --- a/drivers/usb/core/port.c
>>>> +++ b/drivers/usb/core/port.c
>>>> @@ -285,6 +285,14 @@ static int usb_port_runtime_suspend(struct device  
>>>> *dev)
>>>> }
>>>> #endif
>>>>
>>>> +static void usb_port_shutdown(struct device *dev)
>>>> +{
>>>> +	struct usb_port *port_dev = to_usb_port(dev);
>>>> +
>>>> +	if (port_dev->child)
>>>> +		usb_disable_usb2_hardware_lpm(port_dev->child);
>>>> +}
>>>> +
>>>> static const struct dev_pm_ops usb_port_pm_ops = {
>>>> #ifdef CONFIG_PM
>>>> 	.runtime_suspend =	usb_port_runtime_suspend,
>>>> @@ -301,6 +309,7 @@ struct device_type usb_port_device_type = {
>>>> static struct device_driver usb_port_driver = {
>>>> 	.name = "usb",
>>>> 	.owner = THIS_MODULE,
>>>> +	.shutdown = usb_port_shutdown,
>>>> };
>>>
>>> So you now do this for all ports in the system, no matter what is
>>> plugged in or not.  Are you _SURE_ you want to do that?  It seems like a
>>> big hammer to solve just one single device's problems.
>>
>> Yes I think this should be universally applied.
>>
>> I don’t think the bug only happens to one device. Users won’t find this
>> unless they connect their laptop to a power meter.
>>
>> Platform may not completely cut off USB bus power during shutdown,
>> so the device transits to L1 after system shutdown. Now xHC is disabled
>> so nothing can bring it back to L0 or L2.
>
> It would be great if someone can come up with better ideas.
>
> We can also use other approaches, but currently this is the only way I  
> can think of.

Alan and Mathias,

It would be great if you can review this patch, or give me some suggestion.

Kai-Heng

>
> Kai-Heng
>
>> Kai-Heng
>>
>>> thanks,
>>>
>>> greg k-h


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