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

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Message-ID: <a46b9870-207b-45a1-b3e6-5c13e1857640@oss.qualcomm.com>
Date: Tue, 24 Jun 2025 18:34:14 +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 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.

Regards,
Krishna,