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

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Tue, Aug 12, 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@oss.qualcomm.com>
> ---
>  drivers/usb/dwc3/dwc3-qcom.c | 78 +++++++++++++++++++++++++++++++-----
>  1 file changed, 68 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index a7eaefaeec4d..d89fbb1d8994 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -83,6 +83,8 @@ struct dwc3_qcom {
>  	bool			pm_suspended;
>  	struct icc_path		*icc_path_ddr;
>  	struct icc_path		*icc_path_apps;
> +
> +	enum usb_role		current_role;
>  };
>  
>  #define to_dwc3_qcom(d) container_of((d), struct dwc3_qcom, dwc)
> @@ -111,10 +113,6 @@ static inline void dwc3_qcom_clrbits(void __iomem *base, u32 offset, u32 val)
>  	readl(base + offset);
>  }
>  
> -/*
> - * TODO: Make the in-core role switching code invoke dwc3_qcom_vbus_override_enable(),
> - * validate that the in-core extcon support is functional
> - */
>  static void dwc3_qcom_vbus_override_enable(struct dwc3_qcom *qcom, bool enable)
>  {
>  	if (enable) {
> @@ -560,6 +558,55 @@ static int dwc3_qcom_setup_irq(struct dwc3_qcom *qcom, struct platform_device *p
>  	return 0;
>  }
>  
> +static void dwc3_qcom_set_role_notifier(struct dwc3 *dwc, enum usb_role next_role)

Minor nit: There's no notifier here, can we rename to
dwc3_qcom_pre_set_role() for clarity?

> +{
> +	struct dwc3_qcom *qcom = to_dwc3_qcom(dwc);
> +
> +	if (qcom->current_role == next_role)
> +		return;
> +
> +	if (pm_runtime_resume_and_get(qcom->dev)) {
> +		dev_dbg(qcom->dev, "Failed to resume device\n");

Minor nit: should this be dev_err?

> +		return;
> +	}
> +
> +	if (qcom->current_role == USB_ROLE_DEVICE)
> +		dwc3_qcom_vbus_override_enable(qcom, false);
> +	else if (qcom->current_role != USB_ROLE_DEVICE)
> +		dwc3_qcom_vbus_override_enable(qcom, true);
> +
> +	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)

Minor nit: can we rename to dwc3_qcom_pre_run_stop()

> +{
> +	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;
> +	} else if (qcom->mode == USB_DR_MODE_PERIPHERAL) {
> +		qcom->current_role = USB_ROLE_DEVICE;
> +		dwc3_qcom_vbus_override_enable(qcom, true);

Shouldn't you determine if there's connection before setting vbus valid?

There are a couple things that seems at odd to me:
1) Typically we use "vbus override" to describe the vbus control on host
   to turn on/off vbus. Where as here, the vbus override is used for
   vbus valid in device mode for vbus detection.

2) It seems like you always enable vbus valid without checking for
   connection status. You also set vbus valid even if it's in host mode.
   Only when there's role-switch away from device that you'd clear the
   vbus valid.

But I'm not familiar with your platform/design, so I can't judge much on
the above. Base on the description provided, I don't expect functional
issues from your implementation.

I think the comments above should not be blocking your change.

Whether or not you decide to make the updates for the minor nits, here's
my ack:

Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>

BR,
Thinh

> +	} 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);
>  
> -- 
> 2.34.1
>