On 08/07/2015 09:25 AM, Russell King - ARM Linux wrote: > On Fri, Aug 07, 2015 at 03:22:56PM +0200, Sebastian Andrzej Siewior wrote: >> For TX-transfers, I would need to update the start-address so the >> transfers begins where it stopped. However based on your concern I >> can't really assume that the position reported by the HW is the correct >> one. > > Exactly - I don't believe that existing OMAP DMA hardware can ever support > pausing a mem-to-device transfer without data loss as you have no idea > how many bytes have been prefetched by the DMA, and therefore you have > no idea how many bytes to unwind the hardware position. It gets worse > than that when you have to cross into the previous descriptor. It's > really not nice. > > So, disallowing pause for mem-to-device is entirely reasonable given the > data loss implications. Thanks for adding your hard-won knowledge to this discussion, Russell. This saves us a bunch of wasted effort trying to fix x_char with DMA (and TCSANOW termios changes and throttling). Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
