On Mon, Mar 05, 2018 at 10:16:49AM +0200, Felipe Balbi wrote: > > Hi, > > Bin Liu <b-liu@xxxxxx> writes: > > I am relatively new to xhci and its driver. I am trying to get a xhci > > driver runtime log to understand how it handles usb transactions, but I > > don't get much information with dynamic debug (module xhci_hcd) or > > enabling xhci trace events. Is there any other methods you guys use to > > debug xhci driver? > > tracepoints, the best thing since sliced bread ;-) I know, but I didn't get any trace log in bulk IN transfers :( It turns out - I was on v4.9, which doesn't have much tracepoints. Now I see you added more since v4.11. I will try to move to the latest kernel. > > > BTY, the issue I am trying to debug is when reading bulk IN data from a > > USB2.0 device, if the device doesn't have data to transmit and NAKs the > > IN packet, after 4 pairs of IN-NAK transactions, xhci stops sending > > further IN tokens until the next SOF, which leaves ~90us gape on the > > bus. > > > > But when reading data from a USB2.0 thumb drive, this issue doesn't > > happen, even if the device NAKs the IN tokens, xhci still keeps sending > > IN tokens, which is way more than 4 pairs of IN-NAK transactions. > > Thumb drive has Bulk endpoints, what is the other device's transfer type? It is bulk too. I asked for device descriptors. This is a remote debug effort for me, I don't have that device... > > > Any one has a clue on what causes xhci to stop sending IN tokens after > > the device NAK'd 4 times? > > tracepoints, please :-) I will :) I checked the xhci spec, but didn't find any info on what controls xhci's behavor on IN-NAK... 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
