On Fri, Dec 08, 2023 at 02:04:58PM -0700, Sam Edwards wrote: > The DWC3 core can be configured (during IP instantiation, and/or via > configuration signals) not to have any USB3 ports. Some SoCs, however, > may have USB3 interfaces enabled that do not have USB3 PHYs driving > them. This can be due to a few circumstances, including: > a) The hardware designer didn't include USB3 PHYs and neglected to > disable the DWC3 core's USB ports (I know of no instance where this > has actually happened, however, and it seems pretty unlikely). > b) The USB3 PHYs are present but powered off. Perhaps a driver to enable > the PHYs has not yet been written or merged, or USB3 capability is > unneeded in the system and the system designer would like to conserve > power. > c) The USB3 PHYs are muxed to a different controller. This can happen if > the PHYs support non-USB protocols and one of these alternate > functions is needed instead. > > In these circumstances, if the DWC3 does not receive clear link status > indication on an enabled USB3 port, the DWC3 may not allow even USB2 > to function: in host mode, the DWC3 generates an endless barrage of > PORT_CSC status on the accompanying USB2 port, and the xHCI driver is > unable to bring the USB2 port to a functioning state. > > Fix this by first checking if the maximum-speed property in the DT > permits USB3. If not, pass the new `disable-usb3;` property to the > virtual xHCI device, causing the xHCI driver not to enable the USB3 > ports. This allows USB2 to function even with USB3 PHYs > missing/misbehaving, and may be useful even when the USB3 PHYs are > well-behaved: a DT author may know that USB3 support is intact, but > disconnected (not exposed off-board) and choose to lower the > maximum-speed property to avoid an unusable USB3 rhub showing up in > sysfs/lsusb where it may mislead end-users. > > Signed-off-by: Sam Edwards <CFSworks@xxxxxxxxx> > --- > drivers/usb/dwc3/host.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) Where is patch 1/2 of this series? confused, greg k-h
