On Wed, Oct 14, 2015 at 06:02:18PM +0300, Peter Ujfalusi wrote: > On 10/14/2015 05:41 PM, Vinod Koul wrote: > > On Wed, Oct 14, 2015 at 04:12:13PM +0300, Peter Ujfalusi wrote: > >> @@ -1320,41 +1317,92 @@ static struct dma_async_tx_descriptor *edma_prep_dma_memcpy( > >> struct dma_chan *chan, dma_addr_t dest, dma_addr_t src, > >> size_t len, unsigned long tx_flags) > >> { > >> - int ret; > >> + int ret, nslots; > >> struct edma_desc *edesc; > >> struct device *dev = chan->device->dev; > >> struct edma_chan *echan = to_edma_chan(chan); > >> - unsigned int width; > >> + unsigned int width, pset_len; > >> > >> if (unlikely(!echan || !len)) > >> return NULL; > >> > >> - edesc = kzalloc(sizeof(*edesc) + sizeof(edesc->pset[0]), GFP_ATOMIC); > >> + if (len < SZ_64K) { > >> + /* > >> + * Transfer size less than 64K can be handled with one paRAM > >> + * slot. ACNT = length > >> + */ > >> + width = len; > >> + pset_len = len; > >> + nslots = 1; > >> + } else { > >> + /* > >> + * Transfer size bigger than 64K will be handled with maximum of > >> + * two paRAM slots. > >> + * slot1: ACNT = 32767, length1: (length / 32767) > >> + * slot2: the remaining amount of data. > >> + */ > >> + width = SZ_32K - 1; > >> + pset_len = rounddown(len, width); > >> + /* One slot is enough for lengths multiple of (SZ_32K -1) */ > > > > Hmm so does this mean if I have 140K transfer, it will do two 64K for 1st > > slot and 12K in second slot ? > > Not exactly. If the size is less than 64K it can be done with one 'burst' but > if it is bigger we need to have two sets of transfer: > 1. 32K blocks > 2. the remaining data > > so in case of 140K: > 4 x 32K followed by 12K Okay this part wasn't very clear to me, can you please add some comment explaining this bit > > > > > Is there a limit on 'blocks' of 64K we can do here? > > 32767 32K blocks is the limit. > > The 64K burst is only possible if the whole transfer is less less than 64K. > With the ACNT counter we can transfer 64K - 1 bytes, but if this is not enough > we need to use the BCNT counter and for that to work the the distance between > the start of 'slot n' and the start of 'slot n+1' need to be less than 32K, > this is the reason why we have 32K 'blocks' to transfer first followed by the > remaining. Okay IIUC, we have option to single burst if its less that 64K using one slot, otherwise split to 32K chunk with 2 slots, or would it be N in that case Really need more documentation here :) -- ~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