Dear maintainer, dear community, I'm new to looking into the linux kernel, but am hoping that this is the right spot to address my problem. Otherwise I would be very thankful, if you could point me in the right direction. I have a problem with a custom usb device on a raspberry pi running a buildroot 64bit linux with a v5.19.14 kernel. I ran into a problem reading data from a custom usb hid device using interrupt transfers. I'm using the python hidapi library (https://pypi.org/project/hidapi/) with the libusb backend. After sending a custom command to the device, the driver changes from usbhid to usbfs. The device starts sending reports of size 1023 bytes to endpoint 0x83. `usb-devices` yields the following output: T: Bus=3D01 Lev=3D03 Prnt=3D13 Port=3D00 Cnt=3D01 Dev#=3D 14 Spd=3D480 MxC= h=3D 0 D: Ver=3D 2.00 Cls=3D00(>ifc ) Sub=3D00 Prot=3D00 MxPS=3D64 #Cfgs=3D 1 C: #Ifs=3D 1 Cfg#=3D 1 Atr=3D80 MxPwr=3D500mA I: If#=3D 0 Alt=3D 0 #EPs=3D 1 Cls=3D03(HID ) Sub=3D00 Prot=3D00 Driver= =3Dusbfs E: Ad=3D83(I) Atr=3D03(Int.) MxPS=3D1024 Ivl=3D125us The reports are numbered by an increasing report id and are available via interrupt transfer approx. every 230 microseconds (1.85 microframes). The device does not retain any old reports. Initially, I get all reports in the correct order, but after some time I start getting reports that I have already received previously. The report ids start to include a shift after a certain number of reports and schematically they look like the following: ... 1,2,...,578, 238,239,...,816, 476,477,...,1054, and so on So there is approximately the same number of consecutive "forward" reports followed by a jump "backwards" by approximately the same number of reports. I snooped the transferred data using the `usbcore.usbfs_snoop` kernel parameter but this slowed things down, so that I started missing reports and could not reproduce the problem. Then I traced the `xhci-hcd` events and observed that the pattern started to occur, when my python process was rescheduled from one cpu-core to another ... python-22331 [000] ..... 174497.068723: xhci_urb_enqueue: ep3in-intr: urb 0000000070a812bc pipe 1073852544 slot 3 length 0/1024 sgs 0/0 stream 0 flags 00010200 python-22331 [000] d.... 174497.068727: xhci_queue_trb: INTR: Buffer 00000004669c9800 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:c python-22331 [000] d.... 174497.068728: xhci_inc_enq: INTR 000000006122f915: enq 0x00000004526bf8f0(0x00000004526bf000) deq 0x00000004526bf8e0(0x00000004526bf000) segs 2 stream 0 free_trbs 500 bounce 1024 cycle 1 python-22331 [000] d.... 174497.068729: xhci_ring_ep_doorbell: Ring doorbell for Slot 3 ep3in <idle>-0 [000] d.h.. 174497.068811: xhci_handle_event: EVENT: TRB 00000004526bf8e0 status 'Short Packet' len 1 slot 3 ep 7 type 'Transfer Event' flags e:c <idle>-0 [000] d.h.. 174497.068814: xhci_handle_transfer: INTR: Buffer 00000004669c9800 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:C <idle>-0 [000] d.h.. 174497.068820: xhci_inc_deq: INTR 000000006122f915: enq 0x00000004526bf8f0(0x00000004526bf000) deq 0x00000004526bf8f0(0x00000004526bf000) segs 2 stream 0 free_trbs 501 bounce 1024 cycle 1 <idle>-0 [000] d.h.. 174497.068822: xhci_urb_giveback: ep3in-intr: urb 0000000070a812bc pipe 1073852544 slot 3 length 1023/1024 sgs 0/0 stream 0 flags 00010200 <idle>-0 [000] d.h.. 174497.068824: xhci_inc_deq: EVENT 000000002a1d7c0b: enq 0x0000000440f9c000(0x0000000440f9c000) deq 0x0000000440f9f620(0x0000000440f9f000) segs 8 stream 0 free_trbs 2039 bounce 0 cycle 0 python-22331 [000] ..... 174497.068894: xhci_urb_enqueue: ep3in-intr: urb 0000000070a812bc pipe 1073852544 slot 3 length 0/1024 sgs 0/0 stream 0 flags 00010200 python-22331 [000] d.... 174497.068899: xhci_queue_trb: INTR: Buffer 00000004669c9800 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:c python-22331 [000] d.... 174497.068900: xhci_inc_enq: INTR 000000006122f915: enq 0x00000004526bf900(0x00000004526bf000) deq 0x00000004526bf8f0(0x00000004526bf000) segs 2 stream 0 free_trbs 500 bounce 1024 cycle 1 python-22331 [000] d.... 174497.068901: xhci_ring_ep_doorbell: Ring doorbell for Slot 3 ep3in <idle>-0 [000] d.h.. 174497.069954: xhci_handle_event: EVENT: TRB 00000004526bf8f0 status 'Short Packet' len 1 slot 3 ep 7 type 'Transfer Event' flags e:c <idle>-0 [000] d.h.. 174497.069957: xhci_handle_transfer: INTR: Buffer 00000004669c9800 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:C <idle>-0 [000] d.h.. 174497.069959: xhci_inc_deq: INTR 000000006122f915: enq 0x00000004526bf900(0x00000004526bf000) deq 0x00000004526bf900(0x00000004526bf000) segs 2 stream 0 free_trbs 501 bounce 1024 cycle 1 <idle>-0 [000] d.h.. 174497.069961: xhci_urb_giveback: ep3in-intr: urb 0000000070a812bc pipe 1073852544 slot 3 length 1023/1024 sgs 0/0 stream 0 flags 00010200 <idle>-0 [000] d.h.. 174497.069962: xhci_inc_deq: EVENT 000000002a1d7c0b: enq 0x0000000440f9c000(0x0000000440f9c000) deq 0x0000000440f9f630(0x0000000440f9f000) segs 8 stream 0 free_trbs 2039 bounce 0 cycle 0 python-22331 [003] ..... 174497.070160: xhci_urb_enqueue: ep3in-intr: urb 00000000a553f707 pipe 1073852544 slot 3 length 0/1024 sgs 0/0 stream 0 flags 00010200 python-22331 [003] d.... 174497.070171: xhci_queue_trb: INTR: Buffer 00000004799b0000 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:c python-22331 [003] d.... 174497.070172: xhci_inc_enq: INTR 000000006122f915: enq 0x00000004526bf910(0x00000004526bf000) deq 0x00000004526bf900(0x00000004526bf000) segs 2 stream 0 free_trbs 500 bounce 1024 cycle 1 python-22331 [003] d.... 174497.070174: xhci_ring_ep_doorbell: Ring doorbell for Slot 3 ep3in <idle>-0 [000] d.h.. 174497.071201: xhci_handle_event: EVENT: TRB 00000004526bf900 status 'Short Packet' len 1 slot 3 ep 7 type 'Transfer Event' flags e:c <idle>-0 [000] d.h.. 174497.071204: xhci_handle_transfer: INTR: Buffer 00000004799b0000 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:C <idle>-0 [000] d.h.. 174497.071206: xhci_inc_deq: INTR 000000006122f915: enq 0x00000004526bf910(0x00000004526bf000) deq 0x00000004526bf910(0x00000004526bf000) segs 2 stream 0 free_trbs 501 bounce 1024 cycle 1 <idle>-0 [000] d.h.. 174497.071208: xhci_urb_giveback: ep3in-intr: urb 00000000a553f707 pipe 1073852544 slot 3 length 1023/1024 sgs 0/0 stream 0 flags 00010200 <idle>-0 [000] d.h.. 174497.071210: xhci_inc_deq: EVENT 000000002a1d7c0b: enq 0x0000000440f9c000(0x0000000440f9c000) deq 0x0000000440f9f640(0x0000000440f9f000) segs 8 stream 0 free_trbs 2039 bounce 0 cycle 0 python-22331 [003] ..... 174497.071269: xhci_urb_enqueue: ep3in-intr: urb 00000000a553f707 pipe 1073852544 slot 3 length 0/1024 sgs 0/0 stream 0 flags 00010200 python-22331 [003] d.... 174497.071272: xhci_queue_trb: INTR: Buffer 00000004799b0000 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:c python-22331 [003] d.... 174497.071273: xhci_inc_enq: INTR 000000006122f915: enq 0x00000004526bf920(0x00000004526bf000) deq 0x00000004526bf910(0x00000004526bf000) segs 2 stream 0 free_trbs 500 bounce 1024 cycle 1 python-22331 [003] d.... 174497.071274: xhci_ring_ep_doorbell: Ring doorbell for Slot 3 ep3in <idle>-0 [000] d.h.. 174497.072330: xhci_handle_event: EVENT: TRB 00000004526bf910 status 'Short Packet' len 1 slot 3 ep 7 type 'Transfer Event' flags e:c <idle>-0 [000] d.h.. 174497.072331: xhci_handle_transfer: INTR: Buffer 00000004799b0000 length 1024 TD size 0 intr 0 type 'Normal' flags b:i:I:c:s:I:e:C <idle>-0 [000] d.h.. 174497.072332: xhci_inc_deq: INTR 000000006122f915: enq 0x00000004526bf920(0x00000004526bf000) deq 0x00000004526bf920(0x00000004526bf000) segs 2 stream 0 free_trbs 501 bounce 1024 cycle 1 <idle>-0 [000] d.h.. 174497.072334: xhci_urb_giveback: ep3in-intr: urb 00000000a553f707 pipe 1073852544 slot 3 length 1023/1024 sgs 0/0 stream 0 flags 00010200 <idle>-0 [000] d.h.. 174497.072334: xhci_inc_deq: EVENT 000000002a1d7c0b: enq 0x0000000440f9c000(0x0000000440f9c000) deq 0x0000000440f9f650(0x0000000440f9f000) segs 8 stream 0 free_trbs 2039 bounce 0 cycle 0 ... Unfortunately, I do not understand the details of the linux usb stack in depth and the details of this log enough to know where to look any further. I am hoping to get some help or pointers to how to attack my problem. I have tried using different libraries (hidapi C, libusb), linux systems (raspberry pi OS, ubuntu), but the problem persisted. Thank you very much for taking the time for reading about my problem and thank you in advance for any advice. Best Thilo Rörig
