On Mon, Mar 16, 2015 at 05:24:34PM +0530, Rameshwar Sahu wrote: > >> >> +static void xgene_dma_free_desc_list_reverse(struct xgene_dma_chan *chan, > >> >> + struct list_head *list) > >> > do we really care about free order? > >> > >> Yes it start dellocation of descriptor by tail. > > and why by tail is not clear. > We can free allocated descriptor in forward order from head or in > reverse order, I just followed here fsldma.c driver. > Does this make sense ?? No, you have two APIs to free list. Why do you need two? > > > > > >> > where are you mapping dma buffers? > >> > >> I didn't get you here. Can you please explain me here what you mean. > >> As per my understanding client should map the dma buffer and give the > >> physical address and size to this callback prep routines. > > not for memcpy, that is true for slave transfers > > > > For mempcy the idea is that drivers will do buffer mapping > > Still I am clear here, why memcpy will do buffer mapping, I see other > drivers and also async_memcpy.c , they only map it and pass mapped > physical dma address to driver. > > Buffer mapping mean you here is dma_map_xxx ?? Am I correct. Yes > > > > >> > why are you calling this here, status check shouldnt do this... > >> > >> Okay, I will remove it. > >> > >> > >> >> + spin_unlock_bh(&chan->lock); > >> >> + return DMA_IN_PROGRESS; > >> > residue here is size of transacation. > >> > >> We can't calculate here residue size. We don't have any controller > >> register which will tell about remaining transaction size. > > Okay if you cant calculate residue why do we have this fn? > > So basically case here for me is completion of dma descriptor > submitted to hw is not same as order of submission to hw. > So scenario coming in multithread running :e.g. let's assume we have > submitted two descriptors first has cookie 1001 and second has 1002, > now 1002 is completed first, so updated last_completed_cookie as 1002 > but not yer checked for dma_tx_status, and then first cookie completes > and update last_completed_cookie as 1001, now second transaction check > for tx_status and it get DMA_IN_PROGRESS, because > last_completed_cookie(1001) is less than second transaction's > cookie(1002). > > Due to this issue I am traversing that transaction in pending list and > running list, if not there means we are done. > > Does this make sense?? That only convinces me that there is something not so correct. To help me understand pls let me know if below is fine: - for a physical channel, do you submit multiple transactions? - if yes, how does DMA deal with multiple transactions, how does it schedule them? -- ~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
