Re: [PATCH] usb: dwc3: turn off VBUS when leaving host mode

[Bin Liu <b-liu@ti.com>]

Hi Felipe,

On Mon, Dec 02, 2019 at 09:41:42AM +0200, Felipe Balbi wrote:
> 
> Hi,
> 
> Roger Quadros <rogerq@ti.com> writes:
> > On 18/11/2019 09:07, Felipe Balbi wrote:
> >> Hi,
> >> 
> >> Bin Liu <b-liu@ti.com> writes:
> >> 
> >>> VBUS should be turned off when leaving the host mode.
> >>> Set GCTL_PRTCAP to device mode in teardown to de-assert DRVVBUS pin to
> >>> turn off VBUS power.
> >>>
> >>> Fixes: 5f94adfeed97 ("usb: dwc3: core: refactor mode initialization to its own function")
> >>> Signed-off-by: Bin Liu <b-liu@ti.com>
> >>> ---
> >>>   drivers/usb/dwc3/core.c | 1 +
> >>>   1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> >>> index 97d6ae3c4df2..76ac9cd54e64 100644
> >>> --- a/drivers/usb/dwc3/core.c
> >>> +++ b/drivers/usb/dwc3/core.c
> >>> @@ -1201,6 +1201,7 @@ static void dwc3_core_exit_mode(struct dwc3 *dwc)
> >>>   		break;
> >>>   	case USB_DR_MODE_HOST:
> >>>   		dwc3_host_exit(dwc);
> >>> +		dwc3_set_prtcap(dwc, DWC3_GCTL_PRTCAP_DEVICE);
> >> 
> >> seems like this should be done as part of dwc3_host_exit()
> >> 
> >
> > That wouldn't work well with OTG case as dwc3_host_exit(dwc) is
> > called when switching roles and we don't want PRTCAP
> > to change from DWC3_GCTL_PRTCAP_OTG.
> 
> if (port != OTG)
>   set_prtcap(DEVICE)

During init, the PRTCAP is set in dwc3_core_init_mode() besides
dwc3_{host,gadget,drd}_init(). So for tearing down setting it in
dwc3_core_exit_mode() would make the code logic symmetric and easy to
understand.

Also it turns out that setting PRTCAP is required for OTG mode too to
de-assert DRVVBUS. If left GCTL[PRTCAP] to OTG, grounding the ID pin
would make the controller to assert DRVVBUS without any software
involved. So the fix should be the following. Please let me know you
comments.

-Bin.

-----------8<------------
diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 97d6ae3c4df2..cede7a8e3605 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -1209,6 +1209,9 @@ static void dwc3_core_exit_mode(struct dwc3 *dwc)
                /* do nothing */
                break;
        }
+
+       /* de-assert DRVVBUS for HOST and OTG mode */
+       dwc3_set_prtcap(dwc, DWC3_GCTL_PRTCAP_DEVICE);
 }

 static void dwc3_get_properties(struct dwc3 *dwc)

> 
> -- 
> balbi