Just some corrections here.. On 08/01/2013 03:28 PM, Joel Fernandes wrote: >>> 2. If the interrupt handler for some reason doesn't complete or get >>> service in time, we will end up DMA'ing incorrect data as events >>> wouldn't stop coming in even if interrupt is not yet handled (in your >>> example linked sets P1 or P2 would be old ones being repeated). Where as >>> with my method, we are not doing any DMA once we finish the current >>> MAX_NR_SG set even if events continue to come. >> >> Where is repetition and possibility of wrong data being transferred? We >> have a linear list of PaRAM sets - not a loop. You would link the end to >> PaRAM set chain to dummy PaRAM set which BTW will not cause missed >> events. The more number of PaRAM sets you add to the chain, the more > > There would have to be a loop, how else would you ensure continuity and > uninterrupted DMA? > > Consider if you have 2 sets of linked sets: > L1 is the first set of Linked sets and L2 is the second. > > When L1 is done, EDMA continues with L2 (due to the link) while > interrupt handler prepares L1. The continuity depends on L1 being linked > to L2. Only the absolute last break up of the MAX_NR_SG linked set will > be linked to Dummy. > > So consider MAX_NR_SG=10, and sg_len = 35 > > L1 - L2 - L1 - L1 - Dummy Should be, L1 - L2 - L1 - L2 - Dummy > > The split would be in number of slots, > 10 - 10 - 10 - 5 - Dummy > >> time CPU gets to intervene before DMA eventually stalls. This is a >> tradeoff system designers can manage. > > Consider what happens in the case where MAX_SG_NR=1 or 2. In that case, > there's a change we might not get enough time for the interrupt handler > to setup next series of linked set. > > Some how this limitation has to be overcome by advising in comments than > MAX_SG_NR should always be greater than a certain number to ensure > proper operation. s/than/that/ Thanks, -Joel -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
