Hi, I've the following problem, which has lead me to believe that for scheduling isoc streams ehci-sched.c should uses the actual isoc urb packetsize instead of wMaxPacketSize. Some webcams, at least those based on stv06xx bridges, have only 1 alt setting, but they have a register which allows one to tell it to send isoc frames which are never bigger then the value set in the register. I've tested this and it works as advertised, when you create isoc urbs with a size < wMaxPacketSize, then normally when trying to stream from the camera, you will get -EMSGSIZE errors (iirc) as the camera sends isoc frames, larger then the buffers in the isoc urbs created. But if you then write the size you created the isoc urbs with to the register in question, things will work. So this seems to works as advertised. I would like to use this feature of the camera to make it work in cases where there is another isoc stream also active (for example a usb 1.1 audio device) and thus there is not enough bandwidth to make the camera stream with wMaxPacketSize sized isoc urbs, so usb_submit_urb() will fail with -ENOSPC. But even if I make the packets smaller (and thus using less bandwidth) I keep getting -ENOSPC, as ehci-sched.c: iso_stream_init() does not look at the size of the submitted urb, but just assumes wMaxPacketSize, which in case of these webcam simply is not necessarily true. As well written drivers for devices which do always send isoc packets up to wMaxPacketSize, should always submit isoc urbs of wMaxPacketSize, changing this inside ehci-sched.c should not impact existing drivers, where as it will help hardware which can be told to always send packets < wMaxPacketSize, this I would like to propose to change ehci-sched.c: iso_stream_init() to use the actual urb size to calculate the amount of needed usecs. I'm willing to write a patch for this, but have not done so far, because if this idea gets shot down it is little use to spend time on such a patch. Regards, Hans -- 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
