mtd: spi-nor: always use bounce buffer for register read/writes

spi-mem layer expects all buffers passed to it to be DMA'able. But
spi-nor layer mostly allocates buffers on stack for reading/writing to
registers and therefore are not DMA'able. Introduce bounce buffer to be
used to read/write to registers. This ensures that buffer passed to
spi-mem layer during register read/writes is DMA'able. With this change
nor->cmd-buf is no longer used, so drop it.

Signed-off-by: Vignesh Raghavendra <[e-mail]>
Reviewed-by: Boris Brezillon <[e-mail]>
Signed-off-by: Tudor Ambarus <[e-mail]>

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

···
 static int read_sr(struct spi_nor *nor)
 {
 	int ret;
-	u8 val;
 
-	ret = nor->read_reg(nor, SPINOR_OP_RDSR, &val, 1);
+	ret = nor->read_reg(nor, SPINOR_OP_RDSR, nor->bouncebuf, 1);
 	if (ret < 0) {
 		pr_err("error %d reading SR\n", (int) ret);
 		return ret;
 	}
 
-	return val;
+	return nor->bouncebuf[0];
 }
 
 /*
···
 static int read_fsr(struct spi_nor *nor)
 {
 	int ret;
-	u8 val;
 
-	ret = nor->read_reg(nor, SPINOR_OP_RDFSR, &val, 1);
+	ret = nor->read_reg(nor, SPINOR_OP_RDFSR, nor->bouncebuf, 1);
 	if (ret < 0) {
 		pr_err("error %d reading FSR\n", ret);
 		return ret;
 	}
 
-	return val;
+	return nor->bouncebuf[0];
 }
 
 /*
···
 static int read_cr(struct spi_nor *nor)
 {
 	int ret;
-	u8 val;
 
-	ret = nor->read_reg(nor, SPINOR_OP_RDCR, &val, 1);
+	ret = nor->read_reg(nor, SPINOR_OP_RDCR, nor->bouncebuf, 1);
 	if (ret < 0) {
 		dev_err(nor->dev, "error %d reading CR\n", ret);
 		return ret;
 	}
 
-	return val;
+	return nor->bouncebuf[0];
 }
 
 /*
···
  */
 static int write_sr(struct spi_nor *nor, u8 val)
 {
-	nor->cmd_buf[0] = val;
-	return nor->write_reg(nor, SPINOR_OP_WRSR, nor->cmd_buf, 1);
+	nor->bouncebuf[0] = val;
+	return nor->write_reg(nor, SPINOR_OP_WRSR, nor->bouncebuf, 1);
 }
 
 /*
···
 			 * We must clear the register to enable normal behavior.
 			 */
 			write_enable(nor);
-			nor->cmd_buf[0] = 0;
-			nor->write_reg(nor, SPINOR_OP_WREAR, nor->cmd_buf, 1);
+			nor->bouncebuf[0] = 0;
+			nor->write_reg(nor, SPINOR_OP_WREAR,
+				       nor->bouncebuf, 1);
 			write_disable(nor);
 		}
 
 		return status;
 	default:
 		/* Spansion style */
-		nor->cmd_buf[0] = enable << 7;
-		return nor->write_reg(nor, SPINOR_OP_BRWR, nor->cmd_buf, 1);
+		nor->bouncebuf[0] = enable << 7;
+		return nor->write_reg(nor, SPINOR_OP_BRWR, nor->bouncebuf, 1);
 	}
 }
 
 static int s3an_sr_ready(struct spi_nor *nor)
 {
 	int ret;
-	u8 val;
 
-	ret = nor->read_reg(nor, SPINOR_OP_XRDSR, &val, 1);
+	ret = nor->read_reg(nor, SPINOR_OP_XRDSR, nor->bouncebuf, 1);
 	if (ret < 0) {
 		dev_err(nor->dev, "error %d reading XRDSR\n", (int) ret);
 		return ret;
 	}
 
-	return !!(val & XSR_RDY);
+	return !!(nor->bouncebuf[0] & XSR_RDY);
 }
 
 static int spi_nor_sr_ready(struct spi_nor *nor)
···
  */
 static int spi_nor_erase_sector(struct spi_nor *nor, u32 addr)
 {
-	u8 buf[SPI_NOR_MAX_ADDR_WIDTH];
 	int i;
 
 	if (nor->flags & SNOR_F_S3AN_ADDR_DEFAULT)
···
 	 * control
 	 */
 	for (i = nor->addr_width - 1; i >= 0; i--) {
-		buf[i] = addr & 0xff;
+		nor->bouncebuf[i] = addr & 0xff;
 		addr >>= 8;
 	}
 
-	return nor->write_reg(nor, nor->erase_opcode, buf, nor->addr_width);
+	return nor->write_reg(nor, nor->erase_opcode, nor->bouncebuf,
+			      nor->addr_width);
 }
 
 /**
···
  */
 static int spansion_quad_enable(struct spi_nor *nor)
 {
-	u8 sr_cr[2] = {0, CR_QUAD_EN_SPAN};
+	u8 *sr_cr = nor->bouncebuf;
 	int ret;
 
+	sr_cr[0] = 0;
+	sr_cr[1] = CR_QUAD_EN_SPAN;
 	ret = write_sr_cr(nor, sr_cr);
 	if (ret)
 		return ret;
···
  */
 static int spansion_no_read_cr_quad_enable(struct spi_nor *nor)
 {
-	u8 sr_cr[2];
+	u8 *sr_cr = nor->bouncebuf;
 	int ret;
 
 	/* Keep the current value of the Status Register. */
···
 static int spansion_read_cr_quad_enable(struct spi_nor *nor)
 {
 	struct device *dev = nor->dev;
-	u8 sr_cr[2];
+	u8 *sr_cr = nor->bouncebuf;
 	int ret;
 
 	/* Check current Quad Enable bit value. */
···
  */
 static int sr2_bit7_quad_enable(struct spi_nor *nor)
 {
-	u8 sr2;
+	u8 *sr2 = nor->bouncebuf;
 	int ret;
 
 	/* Check current Quad Enable bit value. */
-	ret = nor->read_reg(nor, SPINOR_OP_RDSR2, &sr2, 1);
+	ret = nor->read_reg(nor, SPINOR_OP_RDSR2, sr2, 1);
 	if (ret)
 		return ret;
-	if (sr2 & SR2_QUAD_EN_BIT7)
+	if (*sr2 & SR2_QUAD_EN_BIT7)
 		return 0;
 
 	/* Update the Quad Enable bit. */
-	sr2 |= SR2_QUAD_EN_BIT7;
+	*sr2 |= SR2_QUAD_EN_BIT7;
 
 	write_enable(nor);
 
-	ret = nor->write_reg(nor, SPINOR_OP_WRSR2, &sr2, 1);
+	ret = nor->write_reg(nor, SPINOR_OP_WRSR2, sr2, 1);
 	if (ret < 0) {
 		dev_err(nor->dev, "error while writing status register 2\n");
 		return -EINVAL;
···
 	}
 
 	/* Read back and check it. */
-	ret = nor->read_reg(nor, SPINOR_OP_RDSR2, &sr2, 1);
-	if (!(ret > 0 && (sr2 & SR2_QUAD_EN_BIT7))) {
+	ret = nor->read_reg(nor, SPINOR_OP_RDSR2, sr2, 1);
+	if (!(ret > 0 && (*sr2 & SR2_QUAD_EN_BIT7))) {
 		dev_err(nor->dev, "SR2 Quad bit not set\n");
 		return -EINVAL;
 	}
···
 {
 	int ret;
 	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;
-	u8 sr_cr[2] = {0};
+	u8 *sr_cr =  nor->bouncebuf;
 
 	/* Check current Quad Enable bit value. */
 	ret = read_cr(nor);
···
 static const struct flash_info *spi_nor_read_id(struct spi_nor *nor)
 {
 	int			tmp;
-	u8			id[SPI_NOR_MAX_ID_LEN];
+	u8			*id = nor->bouncebuf;
 	const struct flash_info	*info;
 
 	tmp = nor->read_reg(nor, SPINOR_OP_RDID, id, SPI_NOR_MAX_ID_LEN);
···
 static int s3an_nor_scan(struct spi_nor *nor)
 {
 	int ret;
-	u8 val;
 
-	ret = nor->read_reg(nor, SPINOR_OP_XRDSR, &val, 1);
+	ret = nor->read_reg(nor, SPINOR_OP_XRDSR, nor->bouncebuf, 1);
 	if (ret < 0) {
 		dev_err(nor->dev, "error %d reading XRDSR\n", (int) ret);
 		return ret;
···
 	 * The current addressing mode can be read from the XRDSR register
 	 * and should not be changed, because is a destructive operation.
 	 */
-	if (val & XSR_PAGESIZE) {
+	if (nor->bouncebuf[0] & XSR_PAGESIZE) {
 		/* Flash in Power of 2 mode */
 		nor->page_size = (nor->page_size == 264) ? 256 : 512;
 		nor->mtd.writebufsize = nor->page_size;
···
 	nor->reg_proto = SNOR_PROTO_1_1_1;
 	nor->read_proto = SNOR_PROTO_1_1_1;
 	nor->write_proto = SNOR_PROTO_1_1_1;
+
+	/*
+	 * We need the bounce buffer early to read/write registers when going
+	 * through the spi-mem layer (buffers have to be DMA-able).
+	 */
+	nor->bouncebuf_size = PAGE_SIZE;
+	nor->bouncebuf = devm_kmalloc(dev, nor->bouncebuf_size,
+				      GFP_KERNEL);
+	if (!nor->bouncebuf)
+		return -ENOMEM;
 
 	if (name)
 		info = spi_nor_match_id(name);

include/linux/mtd/spi-nor.h

···
  * @mtd:		point to a mtd_info structure
  * @lock:		the lock for the read/write/erase/lock/unlock operations
  * @dev:		point to a spi device, or a spi nor controller device.
+ * @bouncebuf:		bounce buffer used when the buffer passed by the MTD
+ *                      layer is not DMA-able
+ * @bouncebuf_size:	size of the bounce buffer
  * @info:		spi-nor part JDEC MFR id and other info
  * @page_size:		the page size of the SPI NOR
  * @addr_width:		number of address bytes
···
  * @read_proto:		the SPI protocol for read operations
  * @write_proto:	the SPI protocol for write operations
  * @reg_proto		the SPI protocol for read_reg/write_reg/erase operations
- * @cmd_buf:		used by the write_reg
  * @erase_map:		the erase map of the SPI NOR
  * @prepare:		[OPTIONAL] do some preparations for the
  *			read/write/erase/lock/unlock operations
···
 	struct mtd_info		mtd;
 	struct mutex		lock;
 	struct device		*dev;
+	u8			*bouncebuf;
+	size_t			bouncebuf_size;
 	const struct flash_info	*info;
 	u32			page_size;
 	u8			addr_width;
···
 	enum spi_nor_protocol	reg_proto;
 	bool			sst_write_second;
 	u32			flags;
-	u8			cmd_buf[SPI_NOR_MAX_CMD_SIZE];
 	struct spi_nor_erase_map	erase_map;
 
 	int (*prepare)(struct spi_nor *nor, enum spi_nor_ops ops);