[PATCH linux dev-4.17 v2 2/2] mtd: spi-nor: aspeed: limit the maximum SPI frequency

[Andrew Jeffery]

On Fri, 22 Jun 2018, at 16:39, Cédric Le Goater wrote:
> The optimize read algo can choose a 100MHz SPI frequency which might
> be a bit too high for dual output IO on some chips, for the W25Q256 on
> palmetto for instance. The MX66L1G45G on witherspoon should be fine
> though. Also, the second chip of the FMC controller does not get any
> optimize settings for reads. Only the first is configured by U-Boot.
> 
> To fix these two issues, we introduce a "spi-max-frequency" property
> in the device tree which will be used to cap the optimize read
> algorithm and we run the algo on the FMC controller chips as well.
> 
> By default, the frequency setting is 50MHz.
> 
> Signed-off-by: Cédric Le Goater <clg at kaod.org>

Reviewed-by: Andrew Jeffery <andrew at aj.id.au>

> ---
>  drivers/mtd/spi-nor/aspeed-smc.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/aspeed-smc.c b/drivers/mtd/spi-nor/aspeed-smc.c
> index a301895d1f06..c9cd20f199d9 100644
> --- a/drivers/mtd/spi-nor/aspeed-smc.c
> +++ b/drivers/mtd/spi-nor/aspeed-smc.c
> @@ -62,6 +62,7 @@ static const struct aspeed_smc_info fmc_2400_info = {
>  	.ctl0 = 0x10,
>  	.timing = 0x94,
>  	.set_4b = aspeed_smc_chip_set_4b,
> +	.optimize_read = aspeed_smc_optimize_read,
>  };
>  
>  static const struct aspeed_smc_info spi_2400_info = {
> @@ -83,6 +84,7 @@ static const struct aspeed_smc_info fmc_2500_info = {
>  	.ctl0 = 0x10,
>  	.timing = 0x94,
>  	.set_4b = aspeed_smc_chip_set_4b,
> +	.optimize_read = aspeed_smc_optimize_read,
>  };
>  
>  static const struct aspeed_smc_info spi_2500_info = {
> @@ -114,6 +116,7 @@ struct aspeed_smc_chip {
>  	u32 ctl_val[smc_max];			/* control settings */
>  	enum aspeed_smc_flash_type type;	/* what type of flash */
>  	struct spi_nor nor;
> +	u32 clk_rate;
>  };
>  
>  struct aspeed_smc_controller {
> @@ -130,6 +133,8 @@ struct aspeed_smc_controller {
>  	struct aspeed_smc_chip *chips[0];	/* pointers to attached chips */
>  };
>  
> +#define ASPEED_SPI_DEFAULT_FREQ		50000000
> +
>  /*
>   * SPI Flash Configuration Register (AST2500 SPI)
>   *     or
> @@ -993,11 +998,8 @@ static int aspeed_smc_chip_setup_finish(struct 
> aspeed_smc_chip *chip)
>  	dev_info(controller->dev, "read control register: %08x\n",
>  		chip->ctl_val[smc_read]);
>  
> -	/*
> -	 * TODO: get max freq from chip
> -	 */
>  	if (optimize_read && info->optimize_read)
> -		info->optimize_read(chip, 104000000);
> +		info->optimize_read(chip, chip->clk_rate);
>  	return 0;
>  }
>  
> @@ -1051,6 +1053,13 @@ static int aspeed_smc_setup_flash(struct 
> aspeed_smc_controller *controller,
>  			break;
>  		}
>  
> +		if (of_property_read_u32(child, "spi-max-frequency",
> +					 &chip->clk_rate)) {
> +			chip->clk_rate = ASPEED_SPI_DEFAULT_FREQ;
> +		}
> +		dev_info(dev, "Using %d MHz SPI frequency\n",
> +			 chip->clk_rate / 1000000);
> +
>  		chip->controller = controller;
>  		chip->ctl = controller->regs + info->ctl0 + cs * 4;
>  		chip->cs = cs;
> -- 
> 2.13.6
>