Hi, Bin Liu <b-liu@xxxxxx> writes: > On Mon, Mar 05, 2018 at 01:21:42PM -0600, Bin Liu wrote: >> 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? > > By accident, I reproduced the issue if addng a hub in the middle... > any comments about why a hub changes this xhci behavior is appreciated. none off the top of my head. Maybe Mathias can suggest something. >> > tracepoints, please :-) > > I will get tracepoints for cases w/ and w/o a hub. > > Regards, > -Bin. -- balbi
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