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

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Date:   Thu, 6 Jun 2019 16:06:27 +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 15:55, Kai-Heng Feng <kai.heng.feng@...onical.com> wrote:

> 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.

Can I get some advice here?
I really think disabling LPM should be universally applied.

Kai-Heng

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