RFC OMAP DMA engine conversion

Here's another patch - for the OMAP NAND driver.

One thing this doesn't do is configure up the source/destination bursts, which the old code did:

                        omap_set_dma_dest_burst_mode(info->dma_ch,
                                        OMAP_DMA_DATA_BURST_16);
                        omap_set_dma_src_burst_mode(info->dma_ch,
                                        OMAP_DMA_DATA_BURST_16);

In dma-engine speak, I'm using "burst" for the number of elements to transfer for each frame, with frame sync in place (in other words, the number of transfers to occur for every assertion of the DMA request.) That's how burst is defined on other DMA hardware, so I'm not entirely sure at the moment how critical (or what) the above bursts are doing, whether they're configuring the memory side of the transfer or not. I'll take a deeper look into that this evening, but in the mean time, what's below should be a direct conversion.

MTD does have this weirdness that it uses vmalloc regions and passes addresses in vmalloc regions into drivers - I've left that hack in but it is _highly_ undefined whether the DMA activity would be visible via the vmalloc mapping as things currently stand. (You're probably going to be okay with non-aliasing VIPT caches, but VIVT and aliasing VIPT caches are potential random data corruption candidates.) That's a short-coming across many MTD drivers, one which needs sorting out across the board.

 drivers/mtd/nand/omap2.c |   93 +++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 92 insertions(+), 1 deletions(-)

drivers/mtd/nand/omap2.c +92 -2

index c2b0bba..bd4ed08 100644
@@ -9,6 +9,7 @@
  */
 
 #include <linux/platform_device.h>
+#include <linux/dmaengine.h>
 #include <linux/dma-mapping.h>
 #include <linux/delay.h>
 #include <linux/module.h>

@@ -119,6 +120,7 @@ struct omap_nand_info {
 	int				gpmc_cs;
 	unsigned long			phys_base;
 	struct completion		comp;
+	struct dma_chan			*dma;
 	int				dma_ch;
 	int				gpmc_irq;
 	enum {

@@ -336,6 +338,10 @@ static void omap_nand_dma_cb(int lch, u16 ch_status, void *data)
 {
 	complete((struct completion *) data);
 }
+static void omap_nand_dma_callback(void *data)
+{
+	complete((struct completion *) data);
+}
 
 /*
  * omap_nand_dma_transfer: configer and start dma transfer

@@ -373,6 +379,56 @@ static inline int omap_nand_dma_transfer(struct mtd_info *mtd, void *addr,
 		addr = page_address(p1) + ((size_t)addr & ~PAGE_MASK);
 	}
 
+	if (info->dma) {
+		struct dma_async_tx_descriptor *tx;
+		struct scatterlist sg;
+		unsigned n;
+
+		sg_init_one(&sg, addr, len);
+		n = dma_map_sg(info->dma->device->dev, &sg, 1, dir);
+		if (n == 0) {
+			dev_err(&info->pdev->dev,
+				"Couldn't DMA map a %d byte buffer\n", len);
+			goto out_copy;
+		}
+
+		tx = dmaengine_prep_slave_sg(info->dma, &sg, n,
+			is_write ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM,
+			DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+		if (!tx) {
+			dma_unmap_sg(info->dma->device->dev, &sg, 1, dir);
+			goto out_copy;
+		}
+		tx->callback = omap_nand_dma_callback;
+		tx->callback_param = &info->comp;
+		dmaengine_submit(tx);
+
+		/*  configure and start prefetch transfer */
+		ret = gpmc_prefetch_enable(info->gpmc_cs,
+			PREFETCH_FIFOTHRESHOLD_MAX, 0x1, len, is_write);
+		if (ret) {
+			/* PFPW engine is busy, use cpu copy method */
+			dma_unmap_sg(info->dma->device->dev, &sg, 1, dir);
+			goto out_copy;
+		}
+
+		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));
+		while (gpmc_read_status(GPMC_PREFETCH_COUNT) && (tim++ < limit))
+			cpu_relax();
+
+		/* disable and stop the PFPW engine */
+		gpmc_prefetch_reset(info->gpmc_cs);
+
+		dma_unmap_sg(info->dma->device->dev, &sg, 1, dir);
+		return 0;
+	}
+
 	dma_addr = dma_map_single(&info->pdev->dev, addr, len, dir);
 	if (dma_mapping_error(&info->pdev->dev, dma_addr)) {
 		dev_err(&info->pdev->dev,

@@ -405,7 +461,6 @@ static inline int omap_nand_dma_transfer(struct mtd_info *mtd, void *addr,
 		goto out_copy;
 
 	init_completion(&info->comp);
-
 	omap_start_dma(info->dma_ch);
 
 	/* setup and start DMA using dma_addr */

@@ -925,12 +980,16 @@ static int omap_dev_ready(struct mtd_info *mtd)
 	return 1;
 }
 
+extern bool omap_dma_filter_fn(struct dma_chan *chan, void *param);
+
 static int __devinit omap_nand_probe(struct platform_device *pdev)
 {
 	struct omap_nand_info		*info;
 	struct omap_nand_platform_data	*pdata;
 	int				err;
 	int				i, offset;
+	dma_cap_mask_t mask;
+	unsigned sig;
 
 	pdata = pdev->dev.platform_data;
 	if (pdata == NULL) {

@@ -1011,6 +1070,33 @@ static int __devinit omap_nand_probe(struct platform_device *pdev)
 		break;
 
 	case NAND_OMAP_PREFETCH_DMA:
+		dma_cap_zero(mask);
+		dma_cap_set(DMA_SLAVE, mask);
+		sig = OMAP24XX_DMA_GPMC;
+		info->dma = dma_request_channel(mask, omap_dma_filter_fn, &sig);
+		if (!info->dma) {
+			dev_warn(&pdev->dev, "DMA engine request failed\n");
+		} else {
+			struct dma_slave_config cfg;
+			int rc;
+
+			memset(&cfg, 0, sizeof(cfg));
+			cfg.src_addr = info->phys_base;
+			cfg.dst_addr = info->phys_base;
+			cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
+			cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
+			cfg.src_maxburst = 16;
+			cfg.dst_maxburst = 16;
+			rc = dmaengine_slave_config(info->dma, &cfg);
+			if (rc) {
+				dev_err(&pdev->dev, "DMA engine slave config failed: %d\n",
+					rc);
+				goto out_release_mem_region;
+			}
+			info->nand.read_buf   = omap_read_buf_dma_pref;
+			info->nand.write_buf  = omap_write_buf_dma_pref;
+			break;
+		}
 		err = omap_request_dma(OMAP24XX_DMA_GPMC, "NAND",
 				omap_nand_dma_cb, &info->comp, &info->dma_ch);
 		if (err < 0) {

@@ -1110,6 +1196,8 @@ static int __devinit omap_nand_probe(struct platform_device *pdev)
 	return 0;
 
 out_release_mem_region:
+	if (info->dma)
+		dma_release_channel(info->dma);
 	release_mem_region(info->phys_base, NAND_IO_SIZE);
 out_free_info:
 	kfree(info);

@@ -1127,6 +1215,9 @@ static int omap_nand_remove(struct platform_device *pdev)
 	if (info->dma_ch != -1)
 		omap_free_dma(info->dma_ch);
 
+	if (info->dma)
+		dma_release_channel(info->dma);
+
 	if (info->gpmc_irq)
 		free_irq(info->gpmc_irq, info);
 
 
--

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