On Wed, Apr 16, 2014 at 10:28:45AM +0200, Daniel Mack wrote: > Hi Vinod, > > On 04/16/2014 08:45 AM, Vinod Koul wrote: > > On Wed, Apr 09, 2014 at 06:35:15PM +0200, Daniel Mack wrote: > > >> 5. The cookie comparison in the end simply exists to address the fact > >> that we might have operated on an unreleated descriptor, and we have > >> to start over. > >> > >> So in short, the logic will return the bytes that are not yet processed > >> for a specific transaction, which is the expected thing to do, right? > > Looks fine then BUT I have another questions. > > > > Assuming that you have two txn submitted and driver split them to 3 descriptors > > each, then in that case the driver would walk over all 6 descriptors and sum up > > the value, which would lead to incorrect residue. It will work for single > > pending txn only, right? > > No, because each of the two txn would have a different cookie set, and > the residue function is called for one specific cookie so we know which > one we're looking for. That's the reason why we start over if at the end > of an iterated transaction chain, if we recognize that the cookie > doesn't match, we start over. > > > While at it and looking at the code again, I think right solution maybe to > > update the parent child in the descriptors. So on query you simply walk the > > list for all child descriptors and continue. But the parent and child are > > defined under CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH. > > That's another solution, but it's redundant information after all. > Ultimately, it makes the driver more complicated and introduces one more > area of potentially inconsistent pointers. > > > So adding Dan (his updated email id), would it be okay if we make these as > > generic in descriptor and use them to manage larger length transactions in > > drivers? > > It might add to the readability of the drivers, but for the current > case, I don't think it's really necessary. That is because you are maintaining the current descriptors in chain_running. If we use above method then you dont need to use this, right? -- ~Vinod -- 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
