On 10/14/2015 06:41 AM, Roger Quadros wrote: > On 13/10/15 04:38, Franklin S Cooper Jr wrote: >> The prefetch engine sends a dma request once a FIFO threshold has >> been met. No other requests are received until the previous request >> is handled. >> >> Starting an edma transfer (dma_async_issue_pending) results in any >> previous event for the dma channel to be cleared. Therefore, starting >> the prefetch engine before initiating the dma transfer may result in >> the prefetch triggering a dma request but instead of it being handled >> it can end up being cleared. This will result in a hang since the code >> will continue to wait for the dma request to complete. >> >> By initiating the dma request before enabling the prefetch engine this >> race condition is avoided and no dma request are missed/cleared. >> >> Signed-off-by: Franklin S Cooper Jr <fcooper@xxxxxx> >> --- >> drivers/mtd/nand/omap2.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c >> index 957c32f..94d11de 100644 >> --- a/drivers/mtd/nand/omap2.c >> +++ b/drivers/mtd/nand/omap2.c >> @@ -509,6 +509,9 @@ static inline int omap_nand_dma_transfer(struct mtd_info *mtd, void *addr, >> tx->callback_param = &info->comp; >> dmaengine_submit(tx); >> >> + init_completion(&info->comp); >> + dma_async_issue_pending(info->dma); >> + >> /* configure and start prefetch transfer */ >> ret = omap_prefetch_enable(info->gpmc_cs, >> PREFETCH_FIFOTHRESHOLD_MAX, 0x1, len, is_write, info); >> @@ -516,9 +519,6 @@ static inline int omap_nand_dma_transfer(struct mtd_info *mtd, void *addr, >> /* PFPW engine is busy, use cpu copy method */ >> goto out_copy_unmap; >> >> - init_completion(&info->comp); >> - dma_async_issue_pending(info->dma); >> - >> /* setup and start DMA using dma_addr */ > Is the above comment misplaced after this change? Yup you right. > >> wait_for_completion(&info->comp); >> tim = 0; >> > cheers, > -roger -- 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
