linux-kernel - Re: [PATCH v4 2/3] usb: dwc3: qcom: Implement glue callbacks to facilitate runtime suspend

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Message-ID: <7ab4d0b1-30b8-408f-8dd8-85d9fc255704@oss.qualcomm.com>
Date: Tue, 12 Aug 2025 15:53:46 +0530
From: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Bjorn Andersson <bjorn.andersson@....qualcomm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v4 2/3] usb: dwc3: qcom: Implement glue callbacks to
 facilitate runtime suspend



On 8/12/2025 2:39 PM, Konrad Dybcio wrote:
> On 8/12/25 7:55 AM, 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.
> 
> [...]
> 
>> +	if (qcom->current_role == USB_ROLE_DEVICE)
> 
> I think it makes more sense to check for next_role here (we know
> it'll be the opposite of current_role, but this is confusing to read)
> 
>> +		dwc3_qcom_vbus_override_enable(qcom, false);
>> +	else if (qcom->current_role != USB_ROLE_DEVICE)
>> +		dwc3_qcom_vbus_override_enable(qcom, true);
> 
> I think the formerly proposed inline comparison grew on me..
> or at least drop the 'else' condition, '==' only goes two ways
> 

ACK.

>> +
>> +	pm_runtime_mark_last_busy(qcom->dev);
>> +	pm_runtime_put_sync(qcom->dev);
>> +
>> +	/*
>> +	 * Current role changes via usb_role_switch_set_role callback protected
>> +	 * internally by mutex lock.
>> +	 */
>> +	qcom->current_role = next_role;
>> +}
>> +
>> +static void dwc3_qcom_run_stop_notifier(struct dwc3 *dwc, bool is_on)
>> +{
>> +	struct dwc3_qcom *qcom = to_dwc3_qcom(dwc);
>> +
>> +	/*
>> +	 * When autosuspend is enabled and controller goes to suspend
>> +	 * after removing UDC from userspace, the next UDC write needs
>> +	 * setting of QSCRATCH VBUS_VALID to "1" to generate a connect
>> +	 * done event.
>> +	 */
>> +	if (!is_on)
>> +		return;
>> +
>> +	dwc3_qcom_vbus_override_enable(qcom, true);
>> +	pm_runtime_mark_last_busy(qcom->dev);
>> +}
>> +
>> +struct dwc3_glue_ops dwc3_qcom_glue_ops = {
>> +	.pre_set_role	= dwc3_qcom_set_role_notifier,
>> +	.pre_run_stop	= dwc3_qcom_run_stop_notifier,
>> +};
>> +
>>   static int dwc3_qcom_probe(struct platform_device *pdev)
>>   {
>>   	struct dwc3_probe_data	probe_data = {};
>> @@ -636,6 +683,23 @@ static int dwc3_qcom_probe(struct platform_device *pdev)
>>   	if (ignore_pipe_clk)
>>   		dwc3_qcom_select_utmi_clk(qcom);
>>   
>> +	qcom->mode = usb_get_dr_mode(dev);
>> +
>> +	if (qcom->mode == USB_DR_MODE_HOST) {
>> +		qcom->current_role = USB_ROLE_HOST;
> 
> Should we explicitly clear the VBUS override in this and the last branch?
> 

Not necessary. Even if its kept set (somehow carried on from 
bootloader), its still a NOP if dr mode is host or default mode is host.

Regards,
Krishna,

> Konrad
> 
>> +	} else if (qcom->mode == USB_DR_MODE_PERIPHERAL) {
>> +		qcom->current_role = USB_ROLE_DEVICE;
>> +		dwc3_qcom_vbus_override_enable(qcom, true);
>> +	} else {
>> +		if ((device_property_read_bool(dev, "usb-role-switch")) &&
>> +		    (usb_get_role_switch_default_mode(dev) == USB_DR_MODE_HOST))
>> +			qcom->current_role = USB_ROLE_HOST;
>> +		else
>> +			qcom->current_role = USB_ROLE_DEVICE;
>> +	}
>> +
>> +	qcom->dwc.glue_ops = &dwc3_qcom_glue_ops;
>> +
>>   	qcom->dwc.dev = dev;
>>   	probe_data.dwc = &qcom->dwc;
>>   	probe_data.res = &res;
>> @@ -650,12 +714,6 @@ static int dwc3_qcom_probe(struct platform_device *pdev)
>>   	if (ret)
>>   		goto remove_core;
>>   
>> -	qcom->mode = usb_get_dr_mode(dev);
>> -
>> -	/* enable vbus override for device mode */
>> -	if (qcom->mode != USB_DR_MODE_HOST)
>> -		dwc3_qcom_vbus_override_enable(qcom, true);
>> -
>>   	wakeup_source = of_property_read_bool(dev->of_node, "wakeup-source");
>>   	device_init_wakeup(&pdev->dev, wakeup_source);
>>