[PATCH] configs: am62x_evm_*: Fix USB DFU configuration

[Siddharth Vadapalli]

On Fri, Dec 06, 2024 at 11:44:38AM +0200, Roger Quadros wrote:
> 
> 
> On 06/12/2024 11:17, Roger Quadros wrote:
> > Hello Siddharth,
> > 
> > On 06/12/2024 09:19, Siddharth Vadapalli wrote:

[...]

> >> 2. With the understanding that "dr_mode" doesn't have to be host/otg for
> >> the compatible "snps,dwc3" which is tied to drivers/usb/host/xhci-dwc3.c,
> >> do the following to exit probe when "dr_mode" is "peripheral":
> >> -------------------------------------------------------------------------
> >> diff --git a/drivers/usb/host/xhci-dwc3.c b/drivers/usb/host/xhci-dwc3.c
> >> index e3e0ceff43e..edfd7b97a73 100644
> >> --- a/drivers/usb/host/xhci-dwc3.c
> >> +++ b/drivers/usb/host/xhci-dwc3.c
> >> @@ -208,6 +208,8 @@ static int xhci_dwc3_probe(struct udevice *dev)
> >>         writel(reg, &dwc3_reg->g_usb2phycfg[0]);
> >>
> >>         dr_mode = usb_get_dr_mode(dev_ofnode(dev));
> >> +       if (dr_mode == USB_DR_MODE_PERIPHERAL)
> >> +               return -ENODEV;
> >>         if (dr_mode == USB_DR_MODE_OTG &&
> >>             dev_read_bool(dev, "usb-role-switch")) {
> >>                 dr_mode = usb_get_role_switch_default_mode(dev_ofnode(dev));
> >> -------------------------------------------------------------------------
> >> which will still show "xhci-dwc3" in the output of "dm tree" after "usb
> >> start", but the driver won't be probed (absence of "+" in the "Probed"
> >> column of "dm tree" output).
> 
> I realized later that if dr_mode == USB_DR_MODE_OTG/HOST which is the case
> for am62a, then xhci-dwc3.c will still be probed and we have 2 drivers
> probed for the same controller?

Yes, that's true!

> 
> We do not want that right?
> So not having CONFIG_USB_XHCI_DWC3 is still required for am62*.

Yes.

> 
> Maybe we still need some Kconfig guards that prevent both CONFIG_USB_XHCI_DWC3
> and USB_DWC3_GENERIC to be set together as 2 drivers will claim the
> controller if dr_mdoe is USB_DR_MODE_OTG or USB_DR_MODE_HOST.

Looking at the list of compatibles in dwc3-generic.c and focusing on the
compatible "ti,keystone-dwc3", I see that this compatible is present in:
dts/upstream/src/arm/ti/keystone/keystone.dtsi
among other keystone device-tree files. The hierarchy of the nodes and
compatibles for the USB Subsystem and the USB Controller in Keystone is
similar to that of AM62*. The difference however is the following:
A) For non AM62* devices:
	USB Subsystem [Wrapper] driver is dwc3-generic.c
		USB Controller [DWC3] driver is xhci-dwc3.c
B) For AM62* devices:
	USB Subsystem [Wrapper] driver is dwc3-am62.c
	which exposes its own ".glue_configure" callback similar to what
	is done in dwc3-generic.c for other devices.
		USB Controller [DWC3] driver is xhci-dwc3.c
So maybe non AM62* devices have:
	dwc3-generic.c for Subsystem + xhci-dwc3.c for USB Controller
while AM62* devices have:
	dwc3-am62.c for Subsystem + dwc3-generic.c (neither Subsystem
	nor Controller?) + xhci-dwc3.c for USB Controller
We could probably end up with the two driver situation similar to non
AM62* devices if we update dwc3-generic.c to handle the configuration
performed by dwc3-am62.c. But that still means we have two drivers:
dwc3-generic.c and xhci-dwc3.c
Maybe viewing the output of "dm tree" on a non AM62* device with both
CONFIG_USB_XHCI_DWC3 and CONFIG_USB_DWC3_GENERIC enabled will let us
know whether that is a valid configuration or not.

Regards,
Siddharth.