On Thu, Oct 31, 2013 at 11:24:05AM -0400, Cliff Brake wrote: > Hello, > > We are using a linux device as a iPad MFI peripheral. In the current > scenario, the iPad is the USB device, and linux system is the host. > With Apple MFI in this configuration, the only protocol available to > transfer data is HID. We're noticing that when we transfer a lot of > data over HID, the kernel is locked (seems that interrupts are > disabled) for up to 40ms at a time. > > We noticed a big improvement when upgrading from the 3.0 to the 3.12 > kernel, but the problem is still there. The CPU is the TI DM3730 > (same as beaglebone-xm). > > Is this expected? Any suggestions on where to start looking to improve this. I'd focus on the host controller driver, it would be the one that is probably the issue (you can test this with a PC running Linux and a different host controller.) USB transfers cause irqs to be disabled during the callbacks, that's the way the stack is written (people are slowly working on resolving this.) Does holding interrupts off for that long cause problems for you? If so, perhaps you should change hardware platforms? (not to a rpi, those are _way_ worse for USB...) sorry, greg k-h -- 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
