On 02/26/2015 04:33 AM, Mark Brown wrote: > On Tue, Feb 24, 2015 at 06:08:54PM +0200, Stanimir Varbanov wrote: > >> yes, there is a potential race between atomic_inc and dma callback. I >> reordered these calls to save few checks, and now it returns to me. > >> I imagine few options here: > >> - reorder the dmaengine calls and atomic operations, i.e. >> call atomic_inc for rx and tx channels before corresponding >> dmaengine_submit and dmaengine_issue_pending. > >> - have two different dma callbacks and two completions and waiting for >> the two. > >> - manage to receive only one dma callback, i.e. the last transfer in >> case of presence of the rx_buf and tx_buf at the same time. > >> - let me see for better solution. > > Any solution which doesn't make use of atomics is likely to be better, > as I said they are enormously error prone. A more common approach is a > single completion triggering on the RX (for RX only or bidirectional > transfers) or TX if that's the only thing active. For most hardware you > can just use the RX to manage completion since it must of necessity > complete at the same time as or later than the transmit side, transmit > often completes early since the DMA completes when the FIFO is full not > when the data is on the wire. > yep, that's what I wanted to express in third option above. -- regards, Stan -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
