[PATCH v4 2/7] usb: dwc3: Switch to device mode on gadget start

[Sjoerd Simons]

On Fri, 2024-01-12 at 12:39 +0200, Roger Quadros wrote:
> 
> 
> On 12/01/2024 10:52, Sjoerd Simons wrote:
> > When dr_mode is "otg" the dwc3 is initially configured in _OTG
> > mode;
> > However in this mode the gadget functionality doesn't work without
> > further configuration. To resolve that on gadget start switch to
> > _DEVICE
> > mode globally and go back to _OTG on stop again.
> > 
> > For this the dwc3_set_mode is renamed to dwc3_core_set_mode to
> > avoid a
> > conflict with the same function exposed by xhci-dwc3
> 
> Aren't they both doing the same thing? I'd rather define them at one
> place
> i.e. dwc3/core.c.

They twiddle the same registers afaict indeed; but the way to get there
is rather different. So having just one for both really needs a bigger
amount of rework.

> The driver model design for dwc3 looks really broken in u-boot.
> 
> "snps,dwc3" is claimed by xhci-dwc3.c instead of being claimed by
> dwc3/core.c.
> This is probably because at the time USB host was the more needed use
> case at u-boot.
> 
> Ideally dwc3/core.c should claim "snps,dwc3" device and instantiate
> the respective Host/Device/OTG device based on the provided otg mode.
> 
> For Host/Device mode it is straight forwa
> dwc3/core.c does dwc3_set_mode() depending on the mode and:
> for host mode -> register xhci-usb driver.
> for device mode -> register UDC device driver.
> 
> For dual-role mode, the solution is not very clear as I don't think
> there is a role switch framework present
> 
> To begin with, we could probably restrict it to just device mode
> as most platforms were forcing it to device mode in any case as they
> usually have a 2nd USB port that is host only.

Right we don't have role switching; And if we had we'd have to add
support of the Type-C controller on the SK boards which determines the
roles for this.

This one more minimal patch was modelled after the discussion last year
around otg mode[0]. And similar to how the cdns3 driver handles it.
Essentially letting host/gadget mode be determined by the usage rather
then the cables plugged, which is not pretty but works.

While I agree with you this could all be a lot nicer of u-boot did
"proper" OTG/role-switching; I unfortunately don't have the bandwidth
to introduce all of that and it seems a shame to block DFU support on
it. For reference my previous series just set the peripheral role in
the dts which reflects your suggestion of forcing device mode. I'd be
wary to do so in the driver because i would hope the OTG handling in
dwc3 is there for a reason :) 


0: https://lists.denx.de/pipermail/u-boot/2023-August/527709.html


-- 
Sjoerd Simons
Collabora Ltd.