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

[Roger Quadros <rogerq@kernel.org>]

On 04/04/2023 02:37, Thinh Nguyen wrote:
> On Fri, Mar 31, 2023, Roger Quadros wrote:
>> Hi,
>>
>> On 23/03/2023 22:51, Thinh Nguyen wrote:
>>> On Thu, Mar 23, 2023, Roger Quadros wrote:
>>>>
>>>>
>>>> On 23/03/2023 04:17, Thinh Nguyen wrote:
>>>>> On Wed, Mar 22, 2023, Thinh Nguyen wrote:
>>>>>> On Wed, Mar 22, 2023, Roger Quadros wrote:
>>>>>>> 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 rely on PME. The PME is generated from the PMU of the usb controller
>>>>>> when it detects a resume. If your platform supports hibernation and if
>>>>>> the resume signal is connected to the lower layer power manager of your
>>>>>> device, then you can wakeup the system one level at a time. For example,
>>>>>> if your device is a pci device, that wakeup signal would tie to the pci
>>>>>> power manager, waking up the pci layer before waking up the core of the
>>>>>> usb controller. That's how the host wakes up the host system (e.g. from
>>>>>> remote wakeup). For this to work, we expect something similar on the
>>>>>> device side.
>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>> 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.
>>>>>>>
>>>>>>
>>>>>> You may be able to detect vbus change through the connector controller.
>>>>>> However, the usb controller is the one that detects host resume. What
>>>>>> platform specific implementation do you have outside of the usb
>>>>>> controller do you have to get around that?
>>>>>>
>>>>>> I'm not sure if your platform supports hibernation or if the PME signal
>>>>>> on your platform can wakeup the system, but currently dwc3 driver
>>>>>> doesn't handle hibernation (device side). If there's no hibernation,
>>>>>> there's no PME.
>>>>
>>>> No, in this TI SoC, hibernation feature is not supported in the dwc3 core.
>>>>
>>>>>>
>>>>>
>>>>> Actually, I think the dwc3 core is still on during system suspend for
>>>>> you right? Then I think we can use the wakeup event to wakeup system
>>>>> suspend on host resume? You can ignore about PME in this case. You may
>>>>> need to look into what needs stay awake to allow for handling of the
>>>>> dwc3 event.
>>>>
>>>> But in SoC deep-sleep state, all clocks to the dwc3 core are stopped.
>>>> So I'm not sure if dwc3 events will work.
>>>>
>>>
>>> Right, you need to keep those clocks running to detect host resume.
>>> There's still some power saving through the dwc3 controller's handling
>>> in suspend. You may have some limited power saving from other suspended
>>> devices on your setup. However, I don't think we can expect the platform
>>> to go into deep-sleep and also handle host resume.
>>
>> Why not? if the PHY can detect the host resume and wake up the SoC it will
>> work right?
>>
> 
> Hm... I supposed it may be possible. But it may need some unconventional
> design? The dwc3 controller is currently registered to the phy. For that
> to work, your phy needs to be able to talk to both the dwc3 controller
> and some other controller (equivalent to dwc3 PMU) that manages
> power/interrupt. The dwc3 controller would need to relinquish control to
> this other phy controller on suspend. The phy driver would then be able
> to assert interrupt waking up the system on resume sigal detection,
> which in turn relinquish control to the dwc3 controller. All of this has
> to work while the phy signaling remains synchronized with the dwc3
> controller.

My understanding is that all this is taken care by PHY integration design with
DWC3 core on the TI SoC.

> 
> From the patches you sent, I don't see the changes necesssary for this
> to work. If there is something that I'm missing, please also note it or
> add it here to the series.

There is nothing more as the details are taken care by PHY logic and
necessary integration with DWC3.

For the PHY wake-up programming details you have already checked this series [1].

[1] - https://lore.kernel.org/all/20230316131226.89540-1-rogerq@kernel.org/

cheers,
-roger