[U-Boot] [PATCH] kw_spi: fix clock prescaler computation

[Valentin Longchamp <valentin.longchamp@keymile.com>]

Hi Prafulla,

I haven't received feedback about this patch from you. Can I please kindly
remind you about it since I am about to send patches that deal with SPI clk setting.

Thank you.

On 06/29/2012 02:17 PM, Valentin Longchamp wrote:
> The computation was not correct with low clock values: setting a 1MHz
> clock would result in an overlap that would then configure a 25Mhz
> clock.
> 
> This patch implements a correct computation method according to the
> kirkwood functionnal spec. table 629 (Serial Memory Interface
> Configuration Register).
> 
> Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
> cc: Holger Brunck <holger.brunck@keymile.com>
> cc: Prafulla Wadaskar <prafulla@marvell.com>
> ---
>  arch/arm/include/asm/arch-kirkwood/spi.h |    1 +
>  drivers/spi/kirkwood_spi.c               |    5 +++--
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/include/asm/arch-kirkwood/spi.h b/arch/arm/include/asm/arch-kirkwood/spi.h
> index 1d5043f..5a38dc5 100644
> --- a/arch/arm/include/asm/arch-kirkwood/spi.h
> +++ b/arch/arm/include/asm/arch-kirkwood/spi.h
> @@ -38,6 +38,7 @@ struct kwspi_registers {
>  };
>  
>  #define KWSPI_CLKPRESCL_MASK	0x1f
> +#define KWSPI_CLKPRESCL_MIN	0x12
>  #define KWSPI_CSN_ACT		1 /* Activates serial memory interface */
>  #define KWSPI_SMEMRDY		(1 << 1) /* SerMem Data xfer ready */
>  #define KWSPI_IRQUNMASK		1 /* unmask SPI interrupt */
> diff --git a/drivers/spi/kirkwood_spi.c b/drivers/spi/kirkwood_spi.c
> index ee14669..9b3f6a4 100644
> --- a/drivers/spi/kirkwood_spi.c
> +++ b/drivers/spi/kirkwood_spi.c
> @@ -57,8 +57,9 @@ struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
>  	writel(~KWSPI_CSN_ACT | KWSPI_SMEMRDY, &spireg->ctrl);
>  
>  	/* calculate spi clock prescaller using max_hz */
> -	data = ((CONFIG_SYS_TCLK / 2) / max_hz) & KWSPI_CLKPRESCL_MASK;
> -	data |= 0x10;
> +	data = ((CONFIG_SYS_TCLK / 2) / max_hz) + 0x10;
> +	data = data < KWSPI_CLKPRESCL_MIN ? KWSPI_CLKPRESCL_MIN : data;
> +	data = data > KWSPI_CLKPRESCL_MASK ? KWSPI_CLKPRESCL_MASK : data;
>  
>  	/* program spi clock prescaller using max_hz */
>  	writel(KWSPI_ADRLEN_3BYTE | data, &spireg->cfg);
>