linux-kernel - Re: [PATCH v2 2/4] usb: dwc3: qcom: Implement glue callbacks to facilitate runtime suspend

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Message-ID: <27ff2c46-9402-47e6-b5ea-8a1f783220b1@oss.qualcomm.com>
Date: Sun, 13 Jul 2025 14:59:40 +0530
From: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Andersson <bjorn.andersson@....qualcomm.com>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] usb: dwc3: qcom: Implement glue callbacks to
 facilitate runtime suspend



On 7/12/2025 4:59 AM, Thinh Nguyen wrote:
> On Tue, Jun 24, 2025, Krishna Kurapati wrote:
>>
>>
>> On 6/24/2025 5:02 AM, Thinh Nguyen wrote:
>>> On Tue, Jun 10, 2025, Krishna Kurapati wrote:
>>>> On Qualcomm DWC3 dual-role controllers, the conndone/disconnect events in
>>>> device mode are generated by controller when software writes to QSCRATCH
>>>> registers in Qualcomm Glue layer rather than the vbus line being routed to
>>>> dwc3 core IP for it to recognize and generate these events.
>>>>
>>>> UTMI_OTG_VBUS_VALID  bit of QSCRATCH_HS_PHY_CTRL register needs to be set
>>>> to generate a connection done event and to be cleared for the controller to
>>>> generate a disconnect event during cable removal. When the disconnect is
>>>> not generated upon cable removal, the "connected" flag of dwc3 is left
>>>> marked as "true" and it blocks suspend routines and for that to happen upon
>>>> cable removal, the cable disconnect notification coming in via set_role
>>>> call need to be provided to the Qualcomm glue layer as well.
>>>>
>>>> Currently, the way DWC3 core and Qualcomm legacy glue driver are designed,
>>>> there is no mechanism through which the DWC3 core can notify the Qualcomm
>>>> glue layer of any role changes which it receives via role switch. To
>>>> register these glue callbacks at probe time, for enabling core to notify
>>>> glue layer, the legacy Qualcomm driver has no way to find out when the
>>>> child driver probe was successful since it does not check for the same
>>>> during of_platform_populate.
>>>>
>>>> Hence implement the following glue callbacks for flattened Qualcomm glue
>>>> driver:
>>>>
>>>> 1. set_role: To pass role switching information from drd layer to glue.
>>>> This information is needed to identify NONE/DEVICE mode switch and modify
>>>> QSCRATCH to generate connect-done event on device mode entry and disconnect
>>>> event on cable removal in device mode.
>>>>
>>>> 2. run_stop: When booting up in device mode, if autouspend is enabled and
>>>> userspace doesn't write UDC on boot, controller enters autosuspend. After
>>>> this, if the userspace writes to UDC in the future, run_stop notifier is
>>>> required to enable UTMI_OTG_VBUS_VALID of QSCRATCH so that connect done
>>>> event is generated after run_stop(1) is done to finish enumeration.
>>>>
>>>> Signed-off-by: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
>>>> ---
>>>>    drivers/usb/dwc3/dwc3-qcom.c | 82 ++++++++++++++++++++++++++++++++----
>>>>    1 file changed, 73 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
>>>> index ca7e1c02773a..d40b52e2ba01 100644
>>>> --- a/drivers/usb/dwc3/dwc3-qcom.c
>>>> +++ b/drivers/usb/dwc3/dwc3-qcom.c
>>>> @@ -89,6 +89,12 @@ struct dwc3_qcom {
>>>>    	bool			pm_suspended;
>>>>    	struct icc_path		*icc_path_ddr;
>>>>    	struct icc_path		*icc_path_apps;
>>>> +
>>>> +	/*
>>>> +	 * Current role changes via usb_role_switch_set_role callback protected
>>>> +	 * internally by mutex lock.
>>>> +	 */
>>>> +	enum usb_role		current_role;
>>>
>>> Can we just track the current role through dwc3 core instead of an
>>> addition field in the glue?
>>>
>>
>> Core caches only mode. We need ROLE NONE to identify cable connect. So
>> adding that in glue to keep track.
>>
> 
> The controller is always either host or device, not somewhere in
> between. You're using ROLE_NONE to indicate connection, which is a
> separate state.
> 

Yes, but there is no flag that indicates that in dwc structure today. 
Also since only dwc3-qcom needs it at the moment, I added that role info 
in glue layer.

> I feel this should be tracked separately for clarity. The dwc3 also
> tracks the connection state, can we use that?
> 

Are you referring to the "connected" flag in DWC structure ? I see that 
it indicates connection status only in gadget mode.

Regards,
Krishna,