Applied "spi: spi-ti-qspi: Use bounce buffer if read buffer is not DMA'ble" to the spi tree

Commit Message

Mark Brown April 21, 2017, 5:28 p.m. UTC

The patch

   spi: spi-ti-qspi: Use bounce buffer if read buffer is not DMA'ble

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

From c687c46e9e4527c4b4d82bc3cca58c1b08bcfb83 Mon Sep 17 00:00:00 2001
From: Vignesh R <[e-mail]>
Date: Tue, 11 Apr 2017 17:22:25 +0530
Subject: [PATCH] spi: spi-ti-qspi: Use bounce buffer if read buffer is not
 DMA'ble

Flash filesystems like JFFS2, UBIFS and MTD block layer can provide
vmalloc'd or kmap'd buffers that cannot be mapped using dma_map_sg() and
can potentially be in memory region above 32bit addressable region(ie
buffers belonging to memory region backed by LPAE) of DMA, implement
spi_flash_can_dma() interface to inform SPI core not to map such
buffers.
When buffers are not mapped for DMA, then use a pre allocated bounce
buffer(64K = typical flash erase sector size) to read from flash and
then do a copy to actual destination buffer. This is approach is much
faster than using memcpy using CPU and also reduces CPU load.

With this patch, UBIFS read speed is ~18MB/s and CPU utilization <20% on
DRA74 Rev H EVM. Performance degradation is negligible when compared
with non bounce buffer case while using UBIFS.

Signed-off-by: Vignesh R <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>
---
 drivers/spi/spi-ti-qspi.c | 66 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 59 insertions(+), 7 deletions(-)

Patch

diff --git a/drivers/spi/spi-ti-qspi.c b/drivers/spi/spi-ti-qspi.c
index 804914ebfd9d..23a06148b8ae 100644
--- a/drivers/spi/spi-ti-qspi.c
+++ b/drivers/spi/spi-ti-qspi.c
@@ -33,6 +33,7 @@ 
 #include <linux/pinctrl/consumer.h>
 #include <linux/mfd/syscon.h>
 #include <linux/regmap.h>
+#include <linux/sizes.h>
 
 #include <linux/spi/spi.h>
 
@@ -57,6 +58,8 @@  struct ti_qspi {
 	struct ti_qspi_regs     ctx_reg;
 
 	dma_addr_t		mmap_phys_base;
+	dma_addr_t		rx_bb_dma_addr;
+	void			*rx_bb_addr;
 	struct dma_chan		*rx_chan;
 
 	u32 spi_max_frequency;
@@ -126,6 +129,8 @@  struct ti_qspi {
 #define QSPI_SETUP_ADDR_SHIFT		8
 #define QSPI_SETUP_DUMMY_SHIFT		10
 
+#define QSPI_DMA_BUFFER_SIZE            SZ_64K
+
 static inline unsigned long ti_qspi_read(struct ti_qspi *qspi,
 		unsigned long reg)
 {
@@ -429,6 +434,35 @@  static int ti_qspi_dma_xfer(struct ti_qspi *qspi, dma_addr_t dma_dst,
 	return 0;
 }
 
+static int ti_qspi_dma_bounce_buffer(struct ti_qspi *qspi,
+				     struct spi_flash_read_message *msg)
+{
+	size_t readsize = msg->len;
+	void *to = msg->buf;
+	dma_addr_t dma_src = qspi->mmap_phys_base + msg->from;
+	int ret = 0;
+
+	/*
+	 * Use bounce buffer as FS like jffs2, ubifs may pass
+	 * buffers that does not belong to kernel lowmem region.
+	 */
+	while (readsize != 0) {
+		size_t xfer_len = min_t(size_t, QSPI_DMA_BUFFER_SIZE,
+					readsize);
+
+		ret = ti_qspi_dma_xfer(qspi, qspi->rx_bb_dma_addr,
+				       dma_src, xfer_len);
+		if (ret != 0)
+			return ret;
+		memcpy(to, qspi->rx_bb_addr, xfer_len);
+		readsize -= xfer_len;
+		dma_src += xfer_len;
+		to += xfer_len;
+	}
+
+	return ret;
+}
+
 static int ti_qspi_dma_xfer_sg(struct ti_qspi *qspi, struct sg_table rx_sg,
 			       loff_t from)
 {
@@ -496,6 +530,12 @@  static void ti_qspi_setup_mmap_read(struct spi_device *spi,
 		      QSPI_SPI_SETUP_REG(spi->chip_select));
 }
 
+static bool ti_qspi_spi_flash_can_dma(struct spi_device *spi,
+				      struct spi_flash_read_message *msg)
+{
+	return virt_addr_valid(msg->buf);
+}
+
 static int ti_qspi_spi_flash_read(struct spi_device *spi,
 				  struct spi_flash_read_message *msg)
 {
@@ -509,15 +549,12 @@  static int ti_qspi_spi_flash_read(struct spi_device *spi,
 	ti_qspi_setup_mmap_read(spi, msg);
 
 	if (qspi->rx_chan) {
-		if (msg->cur_msg_mapped) {
+		if (msg->cur_msg_mapped)
 			ret = ti_qspi_dma_xfer_sg(qspi, msg->rx_sg, msg->from);
-			if (ret)
-				goto err_unlock;
-		} else {
-			dev_err(qspi->dev, "Invalid address for DMA\n");
-			ret = -EIO;
+		else
+			ret = ti_qspi_dma_bounce_buffer(qspi, msg);
+		if (ret)
 			goto err_unlock;
-		}
 	} else {
 		memcpy_fromio(msg->buf, qspi->mmap_base + msg->from, msg->len);
 	}
@@ -718,6 +755,17 @@  static int ti_qspi_probe(struct platform_device *pdev)
 		ret = 0;
 		goto no_dma;
 	}
+	qspi->rx_bb_addr = dma_alloc_coherent(qspi->dev,
+					      QSPI_DMA_BUFFER_SIZE,
+					      &qspi->rx_bb_dma_addr,
+					      GFP_KERNEL | GFP_DMA);
+	if (!qspi->rx_bb_addr) {
+		dev_err(qspi->dev,
+			"dma_alloc_coherent failed, using PIO mode\n");
+		dma_release_channel(qspi->rx_chan);
+		goto no_dma;
+	}
+	master->spi_flash_can_dma = ti_qspi_spi_flash_can_dma;
 	master->dma_rx = qspi->rx_chan;
 	init_completion(&qspi->transfer_complete);
 	if (res_mmap)
@@ -757,6 +805,10 @@  static int ti_qspi_remove(struct platform_device *pdev)
 	pm_runtime_put_sync(&pdev->dev);
 	pm_runtime_disable(&pdev->dev);
 
+	if (qspi->rx_bb_addr)
+		dma_free_coherent(qspi->dev, QSPI_DMA_BUFFER_SIZE,
+				  qspi->rx_bb_addr,
+				  qspi->rx_bb_dma_addr);
 	if (qspi->rx_chan)
 		dma_release_channel(qspi->rx_chan);