On Fri, 20 Jan 2012, Alan Stern wrote: > This is a serious problem. The gadget API does not specify whether > usb_ep_enable and usb_ep_disable should be able to run in interrupt > context. Consequently we end up with UDC drivers like your DWC thing > in which the routines cannot run in interrupt context, together with > gadget drivers like g_serial which do call them in interrupt context. > > It may be that the best solution is for the composite.c driver to > implement Set-Config and Set-Interface requests in a workqueue, so that > the calls could be made in process context. For now, you can avoid the > problem by not calling dma_alloc_coherent in your endpoint-setup > routine. > > g_file_storage doesn't have this problem because it uses its own kernel > thread for handling these requests. Actually, dma_alloc_coherent() takes a gfp_t parameter, so you should be able to set GFP_ATOMIC and do the allocation from interrupt context. The problem comes from dma_free_coherent(). It unconditionally checks for being called in process context, and gives a warning if not. This check was added a year or two ago, for something in the ARM architecture IIRC. I keep expecting that this will get fixed at some point, but so far it hasn't. -- Paul -- 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
