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

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Message-ID: <20250711232929.5oukafed5lnvsu2v@synopsys.com>
Date: Fri, 11 Jul 2025 23:29:45 +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 24, 2025, Krishna Kurapati wrote:
> 
> 
> 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.
> 

The controller is always either host or device, not somewhere in
between. You're using ROLE_NONE to indicate connection, which is a
separate state.

I feel this should be tracked separately for clarity. The dwc3 also
tracks the connection state, can we use that?

BR,
Thinh