yunhua li <yunhual@xxxxxxxxx> 6:46 PM (2 minutes ago) to linux-usb Hello all For USB 3.0 isochronous endpoint, anyone know how to calculate bandwidth for an XHCI chip? I have 3 isochronous Cameras. Camera1: 1920*1200*16(YUV) *20(FPS) = 737280000 ~ 740Mb/s Camera2: 1200*1200*16(YUV) * 20(FPS) = 460800000 ~ 470Mb/s Camera3: 1200*1200*16(YUV) * 20(FPS) = 460800000 ~ 470Mb/s 16(YUV) is 2 byte YUV encoding for each pixel. 20(FPS) is the frame rate. Total bandwidth 740+470+470 = 1680Mb/s ~ 1.7Gb/s USB 3.0 speed is 5Gbps. count in 10b/8b encoding, is 4Gbps. I know there is some protocol overhead. When I open the 3rd camera with guvcview or other software. I got the following error. xhci_hcd 0000:49:00.0: xhci_check_bandwidth called for udev 000000004bbf2dcd xhci_hcd 0000:49:00.0: // Ding dong! usb 10-2: Not enough bandwidth for new device state. xhci_hcd 0000:49:00.0: xhci_reset_bandwidth called for udev 000000004bbf2dcd usb 10-2: Not enough bandwidth for altsetting 1 the error comes xhci_check_bandwidth from https://elixir.bootlin.com/linux/v5.10.140/source/drivers/usb/host/xhci.c#L2906 xhci_configure_endpoint https://elixir.bootlin.com/linux/v5.10.140/source/drivers/usb/host/xhci.c#L2862 The result is COMP_BANDWIDTH_ERROR or COMP_SECONDARY_BANDWIDTH_ERROR https://elixir.bootlin.com/linux/v5.10.140/source/drivers/usb/host/xhci.c#L2022 The bandwidth check is done by hardware, not software, I just want to know how to calculate the max supported bandwidth for 3 isochronous devices? I tried to read the XHCI spec. https://www.intel.com/content/dam/www/public/us/en/documents/technical-specifications/extensible-host-controler-interface-usb-xhci.pdf But I couldn't figure it out. I appreciate any help, and thanks for your time to read my post. more info: Here is when I open the 1st camera, the kernel print. (1920*1200*2(Byte) = 4608000 uvcvideo: Device requested 46080 B/frame bandwidth. uvcvideo: Selecting alternate setting 1 (46080 B/frame bandwidth). uvcvideo: Device requested 46080 B/frame bandwidth. uvcvideo: Selecting alternate setting 1 (46080 B/frame bandwidth). Regards
