linux-kernel - Re: [PATCH v7 2/5] usb: dwc3: core: Host wake up support from system suspend

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Date:   Wed, 26 May 2021 09:59:33 +0530
From:   Sandeep Maheswaram <sanm@...eaurora.org>
To:     Matthias Kaehlcke <mka@...omium.org>,
        Felipe Balbi <balbi@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Manu Gautam <mgautam@...eaurora.org>
Subject: Re: [PATCH v7 2/5] usb: dwc3: core: Host wake up support from system
 suspend

Hi Felipe,

On 5/13/2021 3:17 AM, Matthias Kaehlcke wrote:
> On Mon, May 03, 2021 at 02:20:23PM +0300, Felipe Balbi wrote:
>> Hi,
>>
>> Sandeep Maheswaram <sanm@...eaurora.org> writes:
>>>> Sandeep Maheswaram <sanm@...eaurora.org> writes:
>>>>> Avoiding phy powerdown when wakeup capable devices are connected
>>>>> by checking phy_power_off flag.
>>>>> Phy should be on to wake up the device from suspend using wakeup capable
>>>>> devices such as keyboard and mouse.
>>>>>
>>>>> Signed-off-by: Sandeep Maheswaram <sanm@...eaurora.org>
>>>>> Reviewed-by: Matthias Kaehlcke <mka@...omium.org>
>>>>> ---
>>>>>    drivers/usb/dwc3/core.c | 7 +++++--
>>>>>    1 file changed, 5 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>>>>> index b6e53d8..bb414c3 100644
>>>>> --- a/drivers/usb/dwc3/core.c
>>>>> +++ b/drivers/usb/dwc3/core.c
>>>>> @@ -1738,7 +1738,7 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
>>>>>    		dwc3_core_exit(dwc);
>>>>>    		break;
>>>>>    	case DWC3_GCTL_PRTCAP_HOST:
>>>>> -		if (!PMSG_IS_AUTO(msg)) {
>>>>> +		if (!PMSG_IS_AUTO(msg) && dwc->phy_power_off) {
>>>> should be able to detect this generically, no? Shouldn't
>>>> device_may_wakeup() be valid here and give you the answer you want?
>>> I think  device_may_wakeup() gives whether the controller is wake up
>>> capable or not.
>> Yes, but it's a bit more than that. Looking at devices.rst we read:
>>
>> If :c:func:`device_may_wakeup(dev)` returns ``true``, the device should be
>> prepared for generating hardware wakeup signals to trigger a system wakeup event
>> when the system is in the sleep state.  For example, :c:func:`enable_irq_wake()`
>> might identify GPIO signals hooked up to a switch or other external hardware,
>> and :c:func:`pci_enable_wake()` does something similar for the PCI PME signal.
>>
>> So, if there is a condition where $this device has to, somehow, deal
>> with wakeup, it should be configured accordingly. This ->phy_power_off
>> flag is telling us the same thing.
>>
>>> But we want to keep phy powered on only when some wakeup capable devices
>>> (eg:keyboard ,mouse ) are connected to controller.
>> Understood, it could be that we're missing some method for propagating
>> that state (i.e. keyboard with PM support) up to the parent device, but
>> that's no excuse to bypass driver boundaries. Wouldn't you agree?
> I'm not sure if device_may_wakeup() is really the right tool for the
> job. This is the current implementation:
>
> static inline bool device_may_wakeup(struct device *dev)
> {
> 	return dev->power.can_wakeup && !!dev->power.wakeup;
> }
>
> IIUC power.can_wakeup specifies whether the device is wakeup
> capable, primarily in physical terms and indicating that the
> driver is ready to handle wakeups, and power.wakeup represents
> the policy which can be changed by userspace.
>
> Supposing the hub is generally wakeup capable that flag
> shouldn't be changed. Neither should be the policy based on
> what is connected to the bus.
Please suggest us how to proceed further with this patch.