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

[Felipe Balbi <balbi@kernel.org>]

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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.

Fair enough, makes sense.

> Also it turns out that setting PRTCAP is required for OTG mode too to

But, then, how do we go back to OTG?

> 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.

But that's expected, no? If port is OTG, then it must obey ID pin rules
specified by OTG. IIRC, dwc3 is OTG 2.x compliant, at least the version
TI uses.

-- 
balbi

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