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

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Message-ID: <20250623233211.aeehndz2nxqovepd@synopsys.com>
Date: Mon, 23 Jun 2025 23:32:14 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        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 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?

BR,
Thinh

>  };
>