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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

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

> +
> +	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?

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);
>