Re: [PATCH 2/2] mtd: spi-nor: cadence-quadspi: Add support for direct access mode

[Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>]

Hi Vignesh,

Le 07/12/2017 à 07:38, Vignesh R a écrit :
> Cadence QSPI controller provides direct access mode through which flash
> can be accessed in a memory-mapped IO mode. This enables read/write to
> flash using memcpy*() functions. This mode provides higher throughput
> for both read/write operations when compared to current indirect mode of
> operation.
> 
> This patch therefore adds support to use QSPI in direct mode. If the
> window reserved in SoC's memory map for MMIO access is less that of
> flash size(like on most SoCFPGA variants), then the driver falls back
> to indirect mode of operation.
> 
> On TI's 66AK2G SoC, with ARM running at 600MHz and QSPI at 96MHz
> switching to direct mode improves read throughput from 3MB/s to 8MB/s.
> 
> Signed-off-by: Vignesh R <vigneshr@ti.com>
> ---
>  drivers/mtd/spi-nor/cadence-quadspi.c | 52 +++++++++++++++++++++++++++++++++--
>  1 file changed, 50 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
> index becc7d714ab8..f8721ed68bc6 100644
> --- a/drivers/mtd/spi-nor/cadence-quadspi.c
> +++ b/drivers/mtd/spi-nor/cadence-quadspi.c
> @@ -58,6 +58,7 @@ struct cqspi_flash_pdata {
>  	u8		data_width;
>  	u8		cs;
>  	bool		registered;
> +	bool		use_direct_mode;
>  };
>  
>  struct cqspi_st {
> @@ -68,6 +69,7 @@ struct cqspi_st {
>  
>  	void __iomem		*iobase;
>  	void __iomem		*ahb_base;
> +	resource_size_t		ahb_size;
>  	struct completion	transfer_complete;
>  	struct mutex		bus_mutex;
>  
> @@ -103,6 +105,7 @@ struct cqspi_st {
>  /* Register map */
>  #define CQSPI_REG_CONFIG			0x00
>  #define CQSPI_REG_CONFIG_ENABLE_MASK		BIT(0)
> +#define CQSPI_REG_CONFIG_ENB_DIR_ACC_CTRL	BIT(7)
>  #define CQSPI_REG_CONFIG_DECODE_MASK		BIT(9)
>  #define CQSPI_REG_CONFIG_CHIPSELECT_LSB		10
>  #define CQSPI_REG_CONFIG_DMA_MASK		BIT(15)
> @@ -569,6 +572,21 @@ static int cqspi_indirect_read_execute(struct spi_nor *nor, u8 *rxbuf,
>  	return ret;
>  }
>  
> +static int cqspi_direct_read_execute(struct spi_nor *nor, u8 *rxbuf,
> +				     loff_t from_addr, const size_t len)
> +{
> +	struct cqspi_flash_pdata *f_pdata = nor->priv;
> +	struct cqspi_st *cqspi = f_pdata->cqspi;
> +	u32 reg;
> +
> +	reg = readl(cqspi->iobase + CQSPI_REG_CONFIG);
> +	reg |= CQSPI_REG_CONFIG_ENB_DIR_ACC_CTRL;
> +	writel(reg, cqspi->iobase + CQSPI_REG_CONFIG);

I guess setting the ENB_DIR_ACC_CTRL bit could be set once for all when you
set use_direct_mode to true, couldn't it?

It may improve the read performance even more. However not expecting much
difference for Page Program operations.

Then you could call directly call mempcy_fromio() from cqspi_read().
Not mandatory for me, since I also like the symmetry of the 2 functions:
cqspi_direct_read_execute() / cqspi_indirect_read_execute().

So it's up to you :)

> +	memcpy_fromio(rxbuf, cqspi->ahb_base + from_addr, len);
> +
> +	return 0;
> +}
> +
>  static int cqspi_write_setup(struct spi_nor *nor)
>  {
>  	unsigned int reg;
> @@ -671,6 +689,21 @@ static int cqspi_indirect_write_execute(struct spi_nor *nor, loff_t to_addr,
>  	return ret;
>  }
>  
> +static int cqspi_direct_write_execute(struct spi_nor *nor, loff_t to_addr,
> +				      const u8 *txbuf, const size_t len)
> +{
> +	struct cqspi_flash_pdata *f_pdata = nor->priv;
> +	struct cqspi_st *cqspi = f_pdata->cqspi;
> +	u32 reg;
> +
> +	reg = readl(cqspi->iobase + CQSPI_REG_CONFIG);
> +	reg |= CQSPI_REG_CONFIG_ENB_DIR_ACC_CTRL;
> +	writel(reg, cqspi->iobase + CQSPI_REG_CONFIG);

Same comment here.

> +	memcpy_toio(cqspi->ahb_base + to_addr, txbuf, len);
> +
> +	return 0;
> +}
> +
>  static void cqspi_chipselect(struct spi_nor *nor)
>  {
>  	struct cqspi_flash_pdata *f_pdata = nor->priv;
> @@ -891,6 +924,7 @@ static int cqspi_set_protocol(struct spi_nor *nor, const int read)
>  static ssize_t cqspi_write(struct spi_nor *nor, loff_t to,
>  			   size_t len, const u_char *buf)
>  {
> +	struct cqspi_flash_pdata *f_pdata = nor->priv;
>  	int ret;
>  
>  	ret = cqspi_set_protocol(nor, 0);
> @@ -901,7 +935,10 @@ static ssize_t cqspi_write(struct spi_nor *nor, loff_t to,
>  	if (ret)
>  		return ret;
>  
> -	ret = cqspi_indirect_write_execute(nor, to, buf, len);
> +	if (f_pdata->use_direct_mode)
> +		ret = cqspi_direct_write_execute(nor, to, buf, len);
> +	else
> +		ret = cqspi_indirect_write_execute(nor, to, buf, len);
>  	if (ret)
>  		return ret;
>  
> @@ -911,6 +948,7 @@ static ssize_t cqspi_write(struct spi_nor *nor, loff_t to,
>  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;
>  	int ret;
>  
>  	ret = cqspi_set_protocol(nor, 1);
> @@ -921,7 +959,10 @@ static ssize_t cqspi_read(struct spi_nor *nor, loff_t from,
>  	if (ret)
>  		return ret;
>  
> -	ret = cqspi_indirect_read_execute(nor, buf, from, len);
> +	if (f_pdata->use_direct_mode)
> +		ret = cqspi_direct_read_execute(nor, buf, from, len);
> +	else
> +		ret = cqspi_indirect_read_execute(nor, buf, from, len);
>  	if (ret)
>  		return ret;
>  
> @@ -1153,6 +1194,12 @@ static int cqspi_setup_flash(struct cqspi_st *cqspi, struct device_node *np)
>  			goto err;
>  
>  		f_pdata->registered = true;
> +
> +		if (mtd->size <= cqspi->ahb_size) {
> +			f_pdata->use_direct_mode = true;
> +			dev_info(nor->dev, "using direct mode for %s\n",
> +				 mtd->name);

Please use dev_dbg() here insted of dev_info(). IMHO, this kind of output
is not really needed by regular users.

Otherwise, the series looks great!

Best regards,

Cyrille

> +		}
>  	}
>  
>  	return 0;
> @@ -1212,6 +1259,7 @@ static int cqspi_probe(struct platform_device *pdev)
>  		dev_err(dev, "Cannot remap AHB address.\n");
>  		return PTR_ERR(cqspi->ahb_base);
>  	}
> +	cqspi->ahb_size = resource_size(res_ahb);
>  
>  	init_completion(&cqspi->transfer_complete);
>  
>