Re: [PATCH v3 1/3] mtd: spi-nor: always use bounce buffer for register read/writes

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 1 Aug 2019 10:00:50 +0530
Vignesh Raghavendra <vigneshr@ti.com> wrote:

> 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 <vigneshr@ti.com>
> ---
> v3: new patch
> 
>  drivers/mtd/spi-nor/spi-nor.c | 71 ++++++++++++++++++++---------------
>  include/linux/mtd/spi-nor.h   |  7 +++-
>  2 files changed, 46 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 03cc788511d5..8685e4ab6a25 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -296,15 +296,14 @@ struct flash_info {
>  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];
>  }
>  
>  /*
> @@ -315,15 +314,14 @@ static int read_sr(struct spi_nor *nor)
>  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];
>  }
>  
>  /*
> @@ -334,15 +332,14 @@ static int read_fsr(struct spi_nor *nor)
>  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];
>  }
>  
>  /*
> @@ -351,8 +348,8 @@ static int read_cr(struct spi_nor *nor)
>   */
>  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);
>  }
>  
>  /*
> @@ -500,31 +497,31 @@ static int set_4byte(struct spi_nor *nor, bool enable)
>  			 * 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)
> @@ -683,7 +680,6 @@ static loff_t spi_nor_s3an_addr_convert(struct spi_nor *nor, unsigned int addr)
>   */
>  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)
> @@ -697,11 +693,12 @@ static int spi_nor_erase_sector(struct spi_nor *nor, u32 addr)
>  	 * 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);
>  }
>  
>  /**
> @@ -1404,9 +1401,11 @@ static int write_sr_cr(struct spi_nor *nor, u8 *sr_cr)
>  {
>  	int ret;
>  
> +	memcpy(nor->bouncebuf, sr_cr, 2);
> +
>  	write_enable(nor);
>  
> -	ret = nor->write_reg(nor, SPINOR_OP_WRSR, sr_cr, 2);
> +	ret = nor->write_reg(nor, SPINOR_OP_WRSR, nor->bouncebuf, 2);
>  	if (ret < 0) {
>  		dev_err(nor->dev,
>  			"error while writing configuration register\n");
> @@ -1599,22 +1598,22 @@ static int spansion_read_cr_quad_enable(struct spi_nor *nor)
>   */
>  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;
> @@ -1627,8 +1626,8 @@ static int sr2_bit7_quad_enable(struct spi_nor *nor)
>  	}
>  
>  	/* 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;
>  	}
> @@ -2180,11 +2179,13 @@ static const struct flash_info *spi_nor_read_id(struct spi_nor *nor)
>  	u8			id[SPI_NOR_MAX_ID_LEN];
>  	const struct flash_info	*info;
>  
> -	tmp = nor->read_reg(nor, SPINOR_OP_RDID, id, SPI_NOR_MAX_ID_LEN);
> +	tmp = nor->read_reg(nor, SPINOR_OP_RDID, nor->bouncebuf,
> +			    SPI_NOR_MAX_ID_LEN);
>  	if (tmp < 0) {
>  		dev_err(nor->dev, "error %d reading JEDEC ID\n", tmp);
>  		return ERR_PTR(tmp);
>  	}
> +	memcpy(id, nor->bouncebuf, SPI_NOR_MAX_ID_LEN);

Why not directly including the change you have in patch 2 (id is a
pointer that points directly to ->bouncebuf) so you can get rid of this
memcpy() here?

>  
>  	for (tmp = 0; tmp < ARRAY_SIZE(spi_nor_ids) - 1; tmp++) {
>  		info = &spi_nor_ids[tmp];
> @@ -4121,6 +4122,16 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
>  	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).

You should probably extend this comment in patch 2 to explain why 4k
should be enough for regular read/write operations.

The patch looks good otherwise.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> +	 */
> +	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);
>  	/* Try to auto-detect if chip name wasn't specified or not found */
> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
> index 9f57cdfcc93d..6b5956a7a65a 100644
> --- a/include/linux/mtd/spi-nor.h
> +++ b/include/linux/mtd/spi-nor.h
> @@ -344,6 +344,9 @@ struct flash_info;
>   * @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
> @@ -356,7 +359,6 @@ struct flash_info;
>   * @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
> @@ -382,6 +384,8 @@ struct spi_nor {
>  	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;
> @@ -394,7 +398,6 @@ struct spi_nor {
>  	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);