Commit 03d3a1df authored Apr 15, 2016 by Cooper Jr., Franklin Committed by Boris Brezillon May 05, 2016

mtd: nand: omap2: Start dma request before enabling prefetch



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 a dma 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@ti.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

parent 77784785

drivers/mtd/nand/omap2.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -503,6 +503,11 @@ 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);

		/* setup and start DMA using dma_addr */
		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);
		@@ -510,10 +515,6 @@ 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 */
		wait_for_completion(&info->comp);
		tim = 0;
		limit = (loops_per_jiffy * msecs_to_jiffies(OMAP_NAND_TIMEOUT_MS));

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