Hi, On Tue, Oct 31, 2017 at 12:56:40PM -0500, Adam Ford wrote: > We have a situation where occasionally the USB glitches where the D- > glitches low at or near an end of frame (EOF) or end of packet (EOP). > We're using the TWL4030 with MUSB on an OMAP3 processor. We cannot > tell where the glitch is originating. > > We're working on resolving this in both hardware and software, but I > was hoping someone might have some insights on how to address it in > software. > > We created a special test fixture to force the D- low for a moment > during the EOP and EOF to attempt to compare the handling of other USB > controllers and/or USB hubs. The reason I think it's unique to the > MUSB controller or the TWL4030, because we cannot reproduce this issue > using other USB controllers and/or other USB controllers handle the > error condition. > > On an older, 3.0.x kernel, if we get a glitch on D-, the MUSB > controller may become unresponsive to the point where a reboot becomes > required. > > Testing this similar scenario with the 4.14-RC kernel, the MUSB > controller drops the connection and re-enumerates almost immediately, > which indicates to me that the error handling is getting better (or > the glitching is reduced somehow). I have not seen a reboot be > required. > > If I connect the same USB devices to a USB Hub and/or other USB > controller and attempt to force this same condition with the test > fixture, the high level USB code does not notice there is an error. > There is no disconnect, no hanging, no loss of data. > > I am not a USB expert, but it seems like we might be able to handle > the error in software and/or retry if necessary without dropping the > connection. Might someone have any ideas or thoughts on how we might > be able to tweak the software? Does the uart console print any log message before re-enumeration happens with v4.14-rc? is there 'Babble'? I cannot tell what could cause the glitches, which seems to be analog related, but I don't think there is any way in software can prevent dropping the connection. I suspect the glitches cause the babble condition, then the musb controller drops the connection, but the musb driver receives the babble event and restarts the enumeration. There is no software control to prevent the controller to drop the connection when babble happens. Regards, -Bin. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
