[U-Boot] [PATCH v2] spi: mxc_spi: Update pre and post divider algorithm

[Dirk Behme]

On 11.05.2013 07:25, Dirk Behme wrote:
> The spi clock divisor is of the form x * (2**y),  or  x  << y, where x is
> 1 to 16, and y is 0 to 15. Note the similarity with floating point numbers.
> Convert the desired divisor to the smallest number which is >= desired divisor,
> and can be represented in this form. The previous algorithm chose a divisor
> which could be almost twice as large as needed.
>
> Signed-off-by: Troy Kisky <troy.kisky at boundarydevices.com>
> Signed-off-by: Dirk Behme <dirk.behme at gmail.com>

While we are talking about a first -rc now, could we get these two patches

http://patchwork.ozlabs.org/patch/242709/

http://patchwork.ozlabs.org/patch/243113/

applied?

Thanks

Dirk

> ---
>
> Notes:
>
> - Changes in v2: Make the alogrithm simpler by removing the -1 as proposed
>                   by Troy. Make the pre_div and post_div u32.
>
> - This replaces v1 of this patch and depends on the previous sent patch
>    http://patchwork.ozlabs.org/patch/242709/
>
>   drivers/spi/mxc_spi.c |   30 ++++++++++++------------------
>   1 file changed, 12 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/spi/mxc_spi.c b/drivers/spi/mxc_spi.c
> index 3e903b3..e87b899 100644
> --- a/drivers/spi/mxc_spi.c
> +++ b/drivers/spi/mxc_spi.c
> @@ -128,8 +128,8 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs, unsigned int cs,
>   		unsigned int max_hz, unsigned int mode)
>   {
>   	u32 clk_src = mxc_get_clock(MXC_CSPI_CLK);
> -	s32 pre_div = 1, post_div = 0, i, reg_ctrl, reg_config;
> -	u32 ss_pol = 0, sclkpol = 0, sclkpha = 0;
> +	s32 reg_ctrl, reg_config;
> +	u32 ss_pol = 0, sclkpol = 0, sclkpha = 0, pre_div = 0, post_div = 0;
>   	struct cspi_regs *regs = (struct cspi_regs *)mxcs->base;
>
>   	if (max_hz == 0) {
> @@ -147,26 +147,20 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs, unsigned int cs,
>   	reg_ctrl |=  MXC_CSPICTRL_EN;
>   	reg_write(&regs->ctrl, reg_ctrl);
>
> -	/*
> -	 * The following computation is taken directly from Freescale's code.
> -	 */
>   	if (clk_src > max_hz) {
> -		pre_div = DIV_ROUND_UP(clk_src, max_hz);
> -		if (pre_div > 16) {
> -			post_div = pre_div / 16;
> -			pre_div = 16;
> -		}
> -		if (post_div != 0) {
> -			for (i = 0; i < 16; i++) {
> -				if ((1 << i) >= post_div)
> -					break;
> -			}
> -			if (i == 16) {
> +		pre_div = (clk_src - 1) / max_hz;
> +		/* fls(1) = 1, fls(0x80000000) = 32, fls(16) = 5 */
> +		post_div = fls(pre_div);
> +		if (post_div > 4) {
> +			post_div -= 4;
> +			if (post_div >= 16) {
>   				printf("Error: no divider for the freq: %d\n",
>   					max_hz);
>   				return -1;
>   			}
> -			post_div = i;
> +			pre_div >>= post_div;
> +		} else {
> +			post_div = 0;
>   		}
>   	}
>
> @@ -174,7 +168,7 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs, unsigned int cs,
>   	reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_SELCHAN(3)) |
>   		MXC_CSPICTRL_SELCHAN(cs);
>   	reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_PREDIV(0x0F)) |
> -		MXC_CSPICTRL_PREDIV(pre_div - 1);
> +		MXC_CSPICTRL_PREDIV(pre_div);
>   	reg_ctrl = (reg_ctrl & ~MXC_CSPICTRL_POSTDIV(0x0F)) |
>   		MXC_CSPICTRL_POSTDIV(post_div);
>
>