On Tue, Jan 30, 2024 at 12:13:22PM -0600, Rob Herring wrote: > On Wed, Jan 24, 2024 at 05:59:00PM +0000, Conor Dooley wrote: > > On Wed, Jan 24, 2024 at 12:47:14PM -0500, Frank Li wrote: > > > On Wed, Jan 24, 2024 at 05:36:42PM +0000, Conor Dooley wrote: > > > > On Fri, Jan 19, 2024 at 04:31:28PM -0500, Frank Li wrote: > > > > > From: Ran Wang <ran.wang_1@xxxxxxx> > > > > > > > > > > When DWC3 is set to host mode by programming register DWC3_GCTL, VBUS > > > > > (or its control signal) will turn on immediately on related Root Hub > > > > > ports. Then the VBUS will be de-asserted for a little while during xhci > > > > > reset (conducted by xhci driver) for a little while and back to normal. > > > > > > > > > > This VBUS glitch might cause some USB devices emuration fail if kernel > > > > > boot with them connected. One SW workaround which can fix this is to > > > > > program all PORTSC[PP] to 0 to turn off VBUS immediately after setting > > > > > host mode in DWC3 driver(per signal measurement result, it will be too > > > > > late to do it in xhci-plat.c or xhci.c). > > > > > > > > > > Signed-off-by: Ran Wang <ran.wang_1@xxxxxxx> > > > > > Reviewed-by: Peter Chen <peter.chen@xxxxxxx> > > > > > Signed-off-by: Frank Li <Frank.Li@xxxxxxx> > > > > > --- > > > > > Documentation/devicetree/bindings/usb/snps,dwc3.yaml | 7 +++++++ > > > > > 1 file changed, 7 insertions(+) > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml > > > > > index 203a1eb66691f..dbf272b76e0b5 100644 > > > > > --- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml > > > > > +++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml > > > > > @@ -273,6 +273,13 @@ properties: > > > > > with an external supply. > > > > > type: boolean > > > > > > > > > > + snps,host-vbus-glitches: > > > > > + description: > > > > > + When set, power off all Root Hub ports immediately after > > > > > + setting host mode to avoid vbus (negative) glitch happen in later > > > > > + xhci reset. And the vbus will back to 5V automatically when reset done. > > > > nit: "will return to" > > > > > > > + type: boolean > > > > > > > > Why do we want to have a property for this at all? The commit message > > > > seems to describe a problem that's limited to specific configurations > > > > and appears to be somethng the driver should do unconditionally. > > > > > > > > Could you explain why this cannot be done unconditionally please? > > > > > > It depends on board design, not all system vbus can be controller by root > > > hub port. If it is always on, it will not trigger this issue. > > > > Okay, that seems reasonable to have a property for. Can you add that > > info to the commit message please? > > But if vbus is always on, then applying the work-around would be a NOP, > right? So you could just apply this unconditionally. Supposed yes. But I have not confidence to apply this unconditionaly. There are too much difference SOC and dwc3 version. Not sure if it brokes something. I think it should apply workround as less as possible. Frank > > Rob
