Hi, >Hi, > >(please don't top-post :-) I have tried my best to meet the format requirement > >"Chow, Watson" <Watson.Chow@xxxxxxxxx> writes: >> Balbi, >> >> Thanks for your quick reply. >> >> Some questions >> >> 1. You mentioned that the max bandwidth in isoc mode (USB3.0) should be >> around 4Gbps. >> >> I have the below calcuation on bandwidth: >> In USB3.0, 1 micro frame would take 125us and can transfer max 45000 bytes >> So, in 1 sec, we will have 8000 micro frames >> >> Max bandwidth = 8000 x 4500 x 8 = 2.88Gbps >> >> Is my understanding correct? > >probably, It's been a while since I've dug through the spec, to be frank > >> 2. To achieve the max throughput, I need to configure the uvc gadget driver >> with below parameters. Am I right? >> >> # modprobe g_webcam streaming_maxpacket=3072 streaming_maxburst=15 >> streaming_interval=1 > >right, but there's an assumption here that the gadget will be able to >feed data in a timely manner. How does the DWC3 driver or the gadget driver handle the case with intermittent drop of the input video streaming? Any recover mechanism? > >> 3. You suggest me to try on kernel v5.12 or the latest v5.13-rc. It looks not >> easy in my side to upgrade the kernel version. It would affect those other >> device drivers I'm currently using. So, do you think there's any short cut >> to fix this problem under my current kernel version - v5.4? > >In that case, you need to ask for support from whoever forces you to >stay with such an old kernel. I believe that would be Xilinx. I have a thought to back port those changes around the dwc3 and gadget driver from the latest kernel version to my kernel (v5.4). Do you think this is feasible? > >> 4. I read through the procedures to capture debug info by debugfs. However, >> in my test with "streaming_maxburst" set to 10 or above, my system would >> crash and I can't pick the log from that point. Any suggestion? > >have a look at ftrace_dump_on_oops. I will explore how to enable this > Btw, do you know which SoC platform can run the UVC gadget in max throughput. Raspberry Pi/TI Beaglebone/i.MX ??? best regards, Watson -----Original Message----- From: Felipe Balbi <balbi@xxxxxxxxxx> Sent: Friday, May 14, 2021 6:32 PM To: Chow, Watson <Watson.Chow@xxxxxxxxx>; linux-usb@xxxxxxxxxxxxxxx Subject: RE: [BUG REPORT] usb: dwc3: Bug while setting the USB transfer bandwidth on UVC gadget driver Hi, (please don't top-post :-) "Chow, Watson" <Watson.Chow@xxxxxxxxx> writes: > Balbi, > > Thanks for your quick reply. > > Some questions > > 1. You mentioned that the max bandwidth in isoc mode (USB3.0) should be > around 4Gbps. > > I have the below calcuation on bandwidth: > In USB3.0, 1 micro frame would take 125us and can transfer max 45000 bytes > So, in 1 sec, we will have 8000 micro frames > > Max bandwidth = 8000 x 4500 x 8 = 2.88Gbps > > Is my understanding correct? probably, It's been a while since I've dug through the spec, to be frank > 2. To achieve the max throughput, I need to configure the uvc gadget driver > with below parameters. Am I right? > > # modprobe g_webcam streaming_maxpacket=3072 streaming_maxburst=15 > streaming_interval=1 right, but there's an assumption here that the gadget will be able to feed data in a timely manner. > 3. You suggest me to try on kernel v5.12 or the latest v5.13-rc. It looks not > easy in my side to upgrade the kernel version. It would affect those other > device drivers I'm currently using. So, do you think there's any short cut > to fix this problem under my current kernel version - v5.4? In that case, you need to ask for support from whoever forces you to stay with such an old kernel. I believe that would be Xilinx. > 4. I read through the procedures to capture debug info by debugfs. However, > in my test with "streaming_maxburst" set to 10 or above, my system would > crash and I can't pick the log from that point. Any suggestion? have a look at ftrace_dump_on_oops. -- balbi
