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? > wait_for_completion(&info->comp); > tim = 0; > cheers, -roger -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
