Hi Russel, On Thu, 18 Jun 2015 10:04:00 +0100 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Wed, Jun 17, 2015 at 05:50:01PM +0800, Herbert Xu wrote: > > On Wed, Jun 17, 2015 at 09:45:33AM +0200, Boris Brezillon wrote: > > > > > > + ret = dma_map_sg(cesa_dev->dev, req->src, creq->src_nents, > > > + DMA_TO_DEVICE); > > > + if (!ret) > > > + return -ENOMEM; > > > + > > > + creq->src_nents = ret; > > > > DMA-API-HOWTO says that you must retain the original nents and > > use it when you call dma_unmap_sg. So I'm afraid one more repost > > is needed :) > > It's worse than that... You're right on that point, but there's an > additional point. > > If dma_map_sg() coalesces scatterlist entries, then ret will be smaller > than src_nents, and ret indicates how many scatterlist entries to be > walked during DMA - you should not use src_nents for that. I couldn't > see where the driver used that information. In fact, the driver seems > to be capable of walking more than src_nents/ret numbers of scatterlist > entries: it just keeps going with sg_next() until it hits the end of > the allocated scatterlist. Yes, I realized that, and I never used the value returned by dma_map_sg() to walk the scatterlist anyway: I was using the sg_next() and sg->length value (which I replaced by sg_dma_len() in v7 as suggested by Herbert). So the ->src_nents assignment to dma_map_sg() return value was just a silly mistake caused by an uncareful read of the DMA-API-HOWTO. Am I missing something else ? Best Regards, Boris -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- 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
