mtd: spi-nor: cadence-quadspi: Add DMA support for direct mode reads

Add support to use DMA over memory mapped reads in direct mode. This
helps in reducing CPU usage from ~100% to ~10% when reading data from
flash. For non-DMA'able/vmalloc'd buffers, driver just falls back to CPU
based memcpy.
Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/spi-nor/cadence-quadspi.c

@@ -18,6 +18,8 @@
 #include <linux/clk.h>
 #include <linux/completion.h>
 #include <linux/delay.h>
+#include <linux/dma-mapping.h>
+#include <linux/dmaengine.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/interrupt.h>
@@ -73,6 +75,10 @@ struct cqspi_st {
 	struct completion	transfer_complete;
 	struct mutex		bus_mutex;
 
+	struct dma_chan		*rx_chan;
+	struct completion	rx_dma_complete;
+	dma_addr_t		mmap_phys_base;
+
 	int			current_cs;
 	int			current_page_size;
 	int			current_erase_size;
@@ -915,11 +921,75 @@ static ssize_t cqspi_write(struct spi_nor *nor, loff_t to,
 	return len;
 }
 
+static void cqspi_rx_dma_callback(void *param)
+{
+	struct cqspi_st *cqspi = param;
+
+	complete(&cqspi->rx_dma_complete);
+}
+
+static int cqspi_direct_read_execute(struct spi_nor *nor, u_char *buf,
+				     loff_t from, size_t len)
+{
+	struct cqspi_flash_pdata *f_pdata = nor->priv;
+	struct cqspi_st *cqspi = f_pdata->cqspi;
+	enum dma_ctrl_flags flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
+	dma_addr_t dma_src = (dma_addr_t)cqspi->mmap_phys_base + from;
+	int ret = 0;
+	struct dma_async_tx_descriptor *tx;
+	dma_cookie_t cookie;
+	dma_addr_t dma_dst;
+
+	if (!cqspi->rx_chan || !virt_addr_valid(buf)) {
+		memcpy_fromio(buf, cqspi->ahb_base + from, len);
+		return 0;
+	}
+
+	dma_dst = dma_map_single(nor->dev, buf, len, DMA_DEV_TO_MEM);
+	if (dma_mapping_error(nor->dev, dma_dst)) {
+		dev_err(nor->dev, "dma mapping failed\n");
+		return -ENOMEM;
+	}
+	tx = dmaengine_prep_dma_memcpy(cqspi->rx_chan, dma_dst, dma_src,
+				       len, flags);
+	if (!tx) {
+		dev_err(nor->dev, "device_prep_dma_memcpy error\n");
+		ret = -EIO;
+		goto err_unmap;
+	}
+
+	tx->callback = cqspi_rx_dma_callback;
+	tx->callback_param = cqspi;
+	cookie = tx->tx_submit(tx);
+	reinit_completion(&cqspi->rx_dma_complete);
+
+	ret = dma_submit_error(cookie);
+	if (ret) {
+		dev_err(nor->dev, "dma_submit_error %d\n", cookie);
+		ret = -EIO;
+		goto err_unmap;
+	}
+
+	dma_async_issue_pending(cqspi->rx_chan);
+	ret = wait_for_completion_timeout(&cqspi->rx_dma_complete,
+					  msecs_to_jiffies(len));
+	if (ret <= 0) {
+		dmaengine_terminate_sync(cqspi->rx_chan);
+		dev_err(nor->dev, "DMA wait_for_completion_timeout\n");
+		ret = -ETIMEDOUT;
+		goto err_unmap;
+	}
+
+err_unmap:
+	dma_unmap_single(nor->dev, dma_dst, len, DMA_DEV_TO_MEM);
+
+	return 0;
+}
+
 static ssize_t cqspi_read(struct spi_nor *nor, loff_t from,
 			  size_t len, u_char *buf)
 {
 	struct cqspi_flash_pdata *f_pdata = nor->priv;
-	struct cqspi_st *cqspi = f_pdata->cqspi;
 	int ret;
 
 	ret = cqspi_set_protocol(nor, 1);
@@ -931,7 +1001,7 @@ static ssize_t cqspi_read(struct spi_nor *nor, loff_t from,
 		return ret;
 
 	if (f_pdata->use_direct_mode)
-		memcpy_fromio(buf, cqspi->ahb_base + from, len);
+		ret = cqspi_direct_read_execute(nor, buf, from, len);
 	else
 		ret = cqspi_indirect_read_execute(nor, buf, from, len);
 	if (ret)
@@ -1100,6 +1170,21 @@ static void cqspi_controller_init(struct cqspi_st *cqspi)
 	cqspi_controller_enable(cqspi, 1);
 }
 
+static void cqspi_request_mmap_dma(struct cqspi_st *cqspi)
+{
+	dma_cap_mask_t mask;
+
+	dma_cap_zero(mask);
+	dma_cap_set(DMA_MEMCPY, mask);
+
+	cqspi->rx_chan = dma_request_chan_by_mask(&mask);
+	if (IS_ERR(cqspi->rx_chan)) {
+		dev_err(&cqspi->pdev->dev, "No Rx DMA available\n");
+		cqspi->rx_chan = NULL;
+	}
+	init_completion(&cqspi->rx_dma_complete);
+}
+
 static int cqspi_setup_flash(struct cqspi_st *cqspi, struct device_node *np)
 {
 	const struct spi_nor_hwcaps hwcaps = {
@@ -1177,6 +1262,9 @@ static int cqspi_setup_flash(struct cqspi_st *cqspi, struct device_node *np)
 			f_pdata->use_direct_mode = true;
 			dev_dbg(nor->dev, "using direct mode for %s\n",
 				mtd->name);
+
+			if (!cqspi->rx_chan)
+				cqspi_request_mmap_dma(cqspi);
 		}
 	}
 
@@ -1237,6 +1325,7 @@ static int cqspi_probe(struct platform_device *pdev)
 		dev_err(dev, "Cannot remap AHB address.\n");
 		return PTR_ERR(cqspi->ahb_base);
 	}
+	cqspi->mmap_phys_base = (dma_addr_t)res_ahb->start;
 	cqspi->ahb_size = resource_size(res_ahb);
 
 	init_completion(&cqspi->transfer_complete);
@@ -1307,6 +1396,9 @@ static int cqspi_remove(struct platform_device *pdev)
 
 	cqspi_controller_enable(cqspi, 0);
 
+	if (cqspi->rx_chan)
+		dma_release_channel(cqspi->rx_chan);
+
 	clk_disable_unprepare(cqspi->clk);
 
 	pm_runtime_put_sync(&pdev->dev);