Hi all, I'm working on a HCD for the i.MX21 and am having problems with DMA alignment [my hardware requires DMA buffers to be aligned on a 4 byte boundary] It seems that the usb core calls dma_map_single() from map_urb_for_dma() but that this only ensures the memory is is a DMAable region, not that it is correctly aligned. Use case is pwc webcam driver which calls usb_control_message() with a non aligned stack allocated buffer pointer. Does this mean the HCD has to handle this? (I ask because a brief look at the existing HCDs didn't turn up anything similar). If so there are probably two non aligned cases : 1) small buffers (<max packet) where the data can be written directly to hardware "data memory" with no DMA 2) large buffers where the full buffer will have to be copied to a suitably aligned buffer and DMA still used. Case 2) is problematic because the buffers could be large [though in practice such buffers should be dynamically allocated and hence aligned]. Regards, Martin -- 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
