[U-Boot] [PATCH v2 2/8] spi: cadence_qspi: Fix baud rate calculation

[Marek Vasut]

On 11/25/2016 03:38 PM, Phil Edworthy wrote:
> With the existing code, when the requested SPI clock rate is near
> to the lowest that can be achieved by the hardware (max divider
> of the ref clock is 32), the generated clock rate is wrong.
> For example, with a 50MHz ref clock, when asked for anything less
> than a 1.5MHz SPI clock, the code sets up the divider to generate
> 25MHz.
> 
> This change fixes the calculation.
> 
> Signed-off-by: Phil Edworthy <phil.edworthy at renesas.com>
> ---
> v2:
>  - Use the DIV_ROUND_UP macro
> ---
>  drivers/spi/cadence_qspi_apb.c | 23 +++++++----------------
>  1 file changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/spi/cadence_qspi_apb.c b/drivers/spi/cadence_qspi_apb.c
> index 2403e71..b9e0df7 100644
> --- a/drivers/spi/cadence_qspi_apb.c
> +++ b/drivers/spi/cadence_qspi_apb.c
> @@ -273,22 +273,13 @@ void cadence_qspi_apb_config_baudrate_div(void *reg_base,
>  	reg = readl(reg_base + CQSPI_REG_CONFIG);
>  	reg &= ~(CQSPI_REG_CONFIG_BAUD_MASK << CQSPI_REG_CONFIG_BAUD_LSB);
>  
> -	div = ref_clk_hz / sclk_hz;
> -
> -	if (div > 32)
> -		div = 32;
> -
> -	/* Check if even number. */
> -	if ((div & 1)) {
> -		div = (div / 2);
> -	} else {
> -		if (ref_clk_hz % sclk_hz)
> -			/* ensure generated SCLK doesn't exceed user
> -			specified sclk_hz */
> -			div = (div / 2);
> -		else
> -			div = (div / 2) - 1;
> -	}
> +	/*
> +	 * The baud_div field in the config reg is 4 bits, and the ref clock is
> +	 * divided by 2 * (baud_div + 1). Round up the divider to ensure the
> +	 * SPI clock rate is less than or equal to the requested clock rate.
> +	 */
> +	div = DIV_ROUND_UP(ref_clk_hz, sclk_hz);
> +	div = DIV_ROUND_UP(div, 2) - 1;

Same as you did for u-boot, right ?

Acked-by: Marek Vasut <marek.vasut at gmail.com>

>  	debug("%s: ref_clk %dHz sclk %dHz Div 0x%x\n", __func__,
>  	      ref_clk_hz, sclk_hz, div);
> 


-- 
Best regards,
Marek Vasut