Here is a more improved approach for DMA support of SG lists of any length in the EDMA DMA Engine driver. In the previous approach [1] we depended on error interrupts to detect missed events and manually retrigger them, however as discussed in [2], there are concerns this can be trouble some for high speed peripherals which may need a more real-time response from the DMA controller. In this approach, we divide the total no of MAX slots per channel, into 2 linked sets which are cyclically linked to each other (the cyclic link between the 2 sets make sure that the DMA is continuous till the whole SG list has exhausted). We then enable completion interrupts on both linked sets which results in recyling/preparing respective linked set with the next set of SG entries. The interrupt handler executes in parallel while the EDMA controller DMA's the next list. This results in no interruption. Special handling is done for first linked set (as we set up both linked sets initially before starting with the DMA), and last one where the cyclic link has to be broken and a link to the Dummy slot has to be created. Also we keep track of whether all pending DMA operations have completed before we can mark it as complete. [1] https://lkml.org/lkml/2013/7/29/312 [2] https://lkml.org/lkml/2013/7/30/54 Joel Fernandes (12): dma: edma: Setup parameters to DMA MAX_NR_SG at a time ARM: edma: Don't clear EMR of channel in edma_stop dma: edma: remove limits on number of slots dma: edma: Write out and handle MAX_NR_SG at a given time ARM: edma: Add function to enable interrupt for a PaRAM slot ARM: edma: Add pr_debug in edma_link dma: edma: Add function to dump a PaRAM set from PaRAM dma: edma: Add one more required slot to MAX slots dma: edma: Implement multiple linked sets for continuity dma: edma: Check if MAX_NR_SG is even in prep function dma: edma: Keep tracking of Pending interrupts (pending_acks) dma: edma: Return if nothing left todo in edma_execute arch/arm/common/edma.c | 18 ++- drivers/dma/edma.c | 279 +++++++++++++++++++++++++++++------- include/linux/platform_data/edma.h | 1 + 3 files changed, 243 insertions(+), 55 deletions(-) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
