On Sat, Aug 15, 2015 at 11:40 AM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: > On 08/15/2015 01:42 AM, Laurent Pinchart wrote: >> On Thursday 16 July 2015 20:36:49 Geert Uytterhoeven wrote: >>> While working on DMA for R-Car Gen2 using the sh-sci serial driver with >>> rcar-dmac, I ran into two issues: >>> >>> 1. Unlike the old shdmac DMA engine driver, the new rcar-dmac DMA >>> engine driver does not support resubmitting a DMA descriptor. >>> I first tried the patch below, until I ran into the race condition, >>> after which I changed sh-sci to not reuse DMA descriptors. >> >> Is reusing descriptors something that the DMA engine API explicitly allows ? > > No. It explicitly forbids it. dmaengine_submit() must always be called in a > pair with dmaenine_prep_*(). But there is some work in-progress to add Thanks for the confirmation! So the sh-sci driver violates the DMA engine API. > support for re-usable descriptors, see > http://www.spinics.net/lists/dmaengine/msg05554.html Thanks, in the same thread: * DMA_CTRL_ACK + - If set, does not mean descriptor can be reused http://www.spinics.net/lists/dmaengine/msg05552.html Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- 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
