On Fri, 4 Sep 2009, Tony Olech wrote: > Hi > I am trying to develop a linux kernel driver for a USB > device and I am initially following the example driver > usb-skeleton.c and also the driver usblcd.c > > The sequence: > > in the file operation ..write(): > usb_alloc_urb() > usb_buffer_alloc(a big buffer) > usb_fill_bulk_urb(for an OUT pipe) > usb_submit_urb() > usb_free_urb() > then in the completion ..callback(): > usb_buffer_free() > the routine dma_free_coherent() is called which calls > WARN_ON(irqs_disabled) > > and because I am running the kernel with all the debugs > and warnings switched on I get a stack dump in the system > log. > > Because I do not want to see warnings unless I am doing > something wrong I have to investigate the (possible) > problem. As far as I can tell the WARN_ON() is completely > spurious. Is that correct?? If so what is the solution > and who will change the drivers that use the same algorithm?? I'm not an expert on this... As I recall, the WARN_ON is not spurious; some architectures (ARM maybe?) do require interrupts to be enabled in dma_free_coherent(). Basically it is a bug in their DMA implementation. Alan Stern -- 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
