Hi Rob, On January 22, 2019 09:03, Rob Herring wrote: > > On Wed, Jan 16, 2019 at 06:48:06AM +0000, Ran Wang wrote: > > When DWC3 is set to host mode by programming register DWC3_GCTL, > VUBS > > s/VUBS/VBUS/ Yes, will fix it in next version. > > (or its control signal) will on immediately on related Root Hub ports. > > /will on/will turn on/ Got it. Thanks. > > Then the VUBS 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> > > --- > > Documentation/devicetree/bindings/usb/dwc3.txt | 3 +++ > > 1 files changed, 3 insertions(+), 0 deletions(-) > > > > diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt > > b/Documentation/devicetree/bindings/usb/dwc3.txt > > index 8e5265e..dadb530 100644 > > --- a/Documentation/devicetree/bindings/usb/dwc3.txt > > +++ b/Documentation/devicetree/bindings/usb/dwc3.txt > > @@ -106,6 +106,9 @@ Optional properties: > > When just one value, which means INCRX burst > mode enabled. When > > more than one value, which means undefined length > INCR burst type > > enabled. The values can be 1, 4, 8, 16, 32, 64, 128 > and 256. > > + - snps,avoid-vbus-glitch-when-set-host: 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. > > Can't you imply this from the compatible string. You should have an SoC > specific compatible. Sorry, not quite get your point here? Actually I have discussed with Soc design guys and Felipe, it seems to be DWC3 native behavior rather than SoC specific issue. https://lkml.org/lkml/2018/11/23/387 https://lkml.org/lkml/2018/12/12/140 I think there could be 2 reasons why we got no report for a long time till now: 1. Most USB devices are not so sensitive to this VBUS glitch, they would works fine. 2. A proper VBUS pump circuit design can successfully filter this glitch out. I have confirmed this with scope, which means some platforms might resolve issue in this way already (some might not, of cause). > Does this even need to be conditional? What would be the harm in doing > this unconditionally for all DWC3 hosts? >From the logic level, I don't see a harm to DWC3 hosts if unconditionally apply this. However, since this is not a only solution (can fix it in HW way), I prefer to let it controlled by property in DTS node for those questionable board already existing in market. Regards, Ran
