On 2018-10-10 07:05, Vinod wrote: > On 24-09-18, 16:00, Peter Ujfalusi wrote: >> From: Grygorii Strashko <grygorii.strashko@xxxxxx> >> >> Certain users can not use right now the DMAengine API due to missing >> features in the core. Prime example is Networking. > > What are the features you have in mind? The two big ones are: 1. Support for out of order completion of descriptors (cookie management) This mostly concerns the DEV_TO_MEM. Currently we have dma_cookie_t (s32) to track which descriptor is completed, which one is issued and which one is pending. It is mandatory that descriptors are completed in the same order as they were issued. We need to have support for out of order completion of the issued descriptors and thus the s32 way of tracking is not working. We basically have three use cases needed to be supported: 1a: in order completion (currently supported by DMAengine) 1b: out of order completion in a channel, descriptors can complete in different order. 1c: out of order completion in a channel, the completion is ordered within 'classification type' of descriptors via the channel If we issue descriptors 1, 2, 3, 4, 5, 6, 7 We could receive back them 1a: 1, 2, 3, 4, 5, 6, 7 1b: 4, 7, 2, 1, 3, 5, 6 in case of 1c we can classify descriptors when issuing: 1(c0), 2(c0), 3(c0), 4(c1), 5(c1), 6(c1), 7(c1) and we receive the back like: 4(c1), 5(c1), 1(c0), 2(c0), 6(c1), 3(c0), 7(c1) The descriptors are coming back in 'random' order, however they are in order within their classification. The must supported one is 1b at the moment, 1c should be reasonably simple to add support for. 2. NAPI support Via NAPI an RX looks something like this: - give the hardware bunch of descriptors to receive packets - when the first packet is received get notification - disable the interrupts - schedule NAPI - in the NAPI poll function read out the completed descriptors one by one, process them, then give back the descriptor (with new buffer) to the hardware. - after poll finished (no more packets or got the number of packets NAPI told us to read out) enable the interrupts and wait for packets to start to flow in. - Péter Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
