Re: [RFC PATCH 2/2] usb: dwc3: Support 'snps,gadget-keep-connect-sys-sleep' feature

[Roger Quadros <rogerq@kernel.org>]

On 21/03/2023 21:05, Thinh Nguyen wrote:
> On Tue, Mar 21, 2023, Thinh Nguyen wrote:
>> On Tue, Mar 21, 2023, Roger Quadros wrote:
>>> Hi Thinh,
>>>
>>> On 20/03/2023 20:52, Thinh Nguyen wrote:
>>>> Hi,
>>>>
>>>> On Mon, Mar 20, 2023, Roger Quadros wrote:
>>>>> Implement 'snps,gadget-keep-connect-sys-sleep' property.
>>>>>
>>>>> Do not stop the gadget controller and disconnect if this
>>>>> property is present and we are connected to a USB Host.
>>>>>
>>>>> Prevent System sleep if Gadget is not in USB suspend.
>>>>>
>>>>> Signed-off-by: Roger Quadros <rogerq@kernel.org>
>>>>> ---
>>>>>  drivers/usb/dwc3/core.c   | 25 +++++++++++++++++++------
>>>>>  drivers/usb/dwc3/core.h   |  2 ++
>>>>>  drivers/usb/dwc3/gadget.c | 25 +++++++++++++++++++++++--
>>>>>  3 files changed, 44 insertions(+), 8 deletions(-)
>>>>>
>>>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>>>>> index 476b63618511..a47bbaa27302 100644
>>>>> --- a/drivers/usb/dwc3/core.c
>>>>> +++ b/drivers/usb/dwc3/core.c
>>>>> @@ -1575,6 +1575,9 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>>>>>  	dwc->dis_split_quirk = device_property_read_bool(dev,
>>>>>  				"snps,dis-split-quirk");
>>>>>  
>>>>> +	dwc->gadget_keep_connect_sys_sleep = device_property_read_bool(dev,
>>>>> +				"snps,gadget-keep-connect-sys-sleep");
>>>>> +
>>>>>  	dwc->lpm_nyet_threshold = lpm_nyet_threshold;
>>>>>  	dwc->tx_de_emphasis = tx_de_emphasis;
>>>>>  
>>>>> @@ -2027,14 +2030,20 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
>>>>>  {
>>>>>  	unsigned long	flags;
>>>>>  	u32 reg;
>>>>> +	int ret;
>>>>>  
>>>>>  	switch (dwc->current_dr_role) {
>>>>>  	case DWC3_GCTL_PRTCAP_DEVICE:
>>>>>  		if (pm_runtime_suspended(dwc->dev))
>>>>>  			break;
>>>>> -		dwc3_gadget_suspend(dwc);
>>>>> +		ret = dwc3_gadget_suspend(dwc);
>>>>> +		if (ret) {
>>>>> +			dev_err(dwc->dev, "gadget not suspended: %d\n", ret);
>>>>> +			return ret;
>>>>> +		}
>>>>>  		synchronize_irq(dwc->irq_gadget);
>>>>> -		dwc3_core_exit(dwc);
>>>>> +		if(!dwc->gadget_keep_connect_sys_sleep)
>>>>> +			dwc3_core_exit(dwc);
>>>>>  		break;
>>>>>  	case DWC3_GCTL_PRTCAP_HOST:
>>>>>  		if (!PMSG_IS_AUTO(msg) && !device_may_wakeup(dwc->dev)) {
>>>>> @@ -2088,11 +2097,15 @@ static int dwc3_resume_common(struct dwc3 *dwc, pm_message_t msg)
>>>>>  
>>>>>  	switch (dwc->current_dr_role) {
>>>>>  	case DWC3_GCTL_PRTCAP_DEVICE:
>>>>> -		ret = dwc3_core_init_for_resume(dwc);
>>>>> -		if (ret)
>>>>> -			return ret;
>>>>> +		if (!dwc->gadget_keep_connect_sys_sleep)
>>>>> +		{
>>>>> +			ret = dwc3_core_init_for_resume(dwc);
>>>>> +			if (ret)
>>>>> +				return ret;
>>>>> +
>>>>> +			dwc3_set_prtcap(dwc, DWC3_GCTL_PRTCAP_DEVICE);
>>>>> +		}
>>>>>  
>>>>> -		dwc3_set_prtcap(dwc, DWC3_GCTL_PRTCAP_DEVICE);
>>>>>  		dwc3_gadget_resume(dwc);
>>>>>  		break;
>>>>>  	case DWC3_GCTL_PRTCAP_HOST:
>>>>> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
>>>>> index 582ebd9cf9c2..f84bac815bed 100644
>>>>> --- a/drivers/usb/dwc3/core.h
>>>>> +++ b/drivers/usb/dwc3/core.h
>>>>> @@ -1328,6 +1328,8 @@ struct dwc3 {
>>>>>  	unsigned		dis_split_quirk:1;
>>>>>  	unsigned		async_callbacks:1;
>>>>>  
>>>>> +	unsigned		gadget_keep_connect_sys_sleep:1;
>>>>> +
>>>>>  	u16			imod_interval;
>>>>>  
>>>>>  	int			max_cfg_eps;
>>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>>> index 3c63fa97a680..8062e44f63f6 100644
>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>> @@ -4572,12 +4572,23 @@ void dwc3_gadget_exit(struct dwc3 *dwc)
>>>>>  int dwc3_gadget_suspend(struct dwc3 *dwc)
>>>>>  {
>>>>>  	unsigned long flags;
>>>>> +	int link_state;
>>>>>  
>>>>>  	if (!dwc->gadget_driver)
>>>>>  		return 0;
>>>>>  
>>>>> -	dwc3_gadget_run_stop(dwc, false, false);
>>>>> +	if (dwc->gadget_keep_connect_sys_sleep && dwc->connected) {
>>>>> +		link_state = dwc3_gadget_get_link_state(dwc);
>>>>> +		/* Prevent PM Sleep if not in U3/L2 */
>>>>> +		if (link_state != DWC3_LINK_STATE_U3)
>>>>> +			return -EBUSY;
>>>>> +
>>>>> +		/* don't stop/disconnect */
>>>>> +		dwc3_gadget_disable_irq(dwc);
>>>>
>>>> We shouldn't disable event interrupt here. What will happen if the
>>>
>>> Due to some reason, if I don't disable the event interrupts here then
>>> after USB resume the USB controller is malfunctioning.
>>> It no longer responds to any requests from Host.
>>
>> You should look into this. These events are important as they can tell
>> whether the host initiates resume.
>>
>>>
>>>> device is disconnected and reconnect to the host while the device is
>>>> still in system suspend? The host would not be able to communicate with
>>>> the device then.
>>>
>>> In the TI platform, The system is woken up on any VBUS/linestate change
>>> and in dwc3_gadget_resume we enable the events again and check for pending
>>> events. Is it pointless to check for pending events there?
>>>
>>
>> It seems fragile for the implementation to be dependent on platform
>> specific feature right?
>>
>> Also, what will happen in a typical case when the host puts the device
>> in suspend and initiates resume while the device is in system suspend
>> (and stay in suspend over a period of time)? There is no VBUS change.
>> There will be problem if host detects no response from device in time.
>>
>> Don't we need these events to wakeup the device?

That's why the TI implementation has line-state change detection to
detect a USB resume. We are doing a out-of-band wake-up. The wake up
events are configured in the wrapper driver (dwc3-am62.c).

Do you know of any dwc3 implementation that uses in-band mechanism
to wake up the System. i.e. it relies on events enabled in DEVTEN register?

>>
> 
> We may not be able to suspend everything in system suspend for this
> case. I'm thinking of treating these events as if they are PME to wakeup
> the device, but they are not the same. It may not be simple to handle
> this. The lower layers may need to stay awake for the dwc3 to handle
> these events. Hm... it gets a bit complicated.

As we are going into suspend, we are not really in a position to handle any
(DEVTEN) events till we have fully resumed.
So yes, we need to rely on platform specific implementation to wake
the System on any USB event.

cheers,
-roger