[U-Boot] [PATCH 3/3] fsl_i2c: Impl. AN2919, rev 5 to calculate FDR/DFSR

[Wolfgang Grandegger <wg@denx.de>]

Hi Joakim,

Joakim Tjernlund wrote:
> The latest AN2919 has changed the way FDR/DFSR should be calculated.
> Update the driver according to spec. However, Condition 2
> is not accounted for as it is not clear how to do so.

I compared rev. 5 of AN2919 with rev. 3 and, as you pointed out, it puts
additional constraints on how to select dfsr and fdr. Especially dfsr
should not exceed a certain, frequency dependent value: dfsr <= 50 /
period-in-ns. Therefore, I expected problems with divider values from
the table which high dfsr values. I did your "=> date;date;date;date"
test on a MPC8548 board using dfsr=43 and fdr=7 but it did not fail.
According to the rev. 5, dfsr is not allowed to be greater than 8.
Your patch works fine on this board as well. I have no time for a more
thorough testing with different CPUs and frequencies. Anyhow...

> Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>

I realized some minor coding style issues, though. See below.

> ---
>  drivers/i2c/fsl_i2c.c |   90 ++++++++++++++++++++++++++++++-------------------
>  1 files changed, 55 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/i2c/fsl_i2c.c b/drivers/i2c/fsl_i2c.c
> index 0c5f6be..78f21c7 100644
> --- a/drivers/i2c/fsl_i2c.c
> +++ b/drivers/i2c/fsl_i2c.c
> @@ -100,29 +100,9 @@ static const struct fsl_i2c *i2c_dev[2] = {
>   */
>  static const struct {
>  	unsigned short divider;
> -#ifdef __PPC__
> -	u8 dfsr;
> -#endif
>  	u8 fdr;
>  } fsl_i2c_speed_map[] = {
> -#ifdef __PPC__
> -	{160, 1, 32}, {192, 1, 33}, {224, 1, 34}, {256, 1, 35},
> -	{288, 1, 0}, {320, 1, 1}, {352, 6, 1}, {384, 1, 2}, {416, 6, 2},
> -	{448, 1, 38}, {480, 1, 3}, {512, 1, 39}, {544, 11, 3}, {576, 1, 4},
> -	{608, 22, 3}, {640, 1, 5}, {672, 32, 3}, {704, 11, 5}, {736, 43, 3},
> -	{768, 1, 6}, {800, 54, 3}, {832, 11, 6}, {896, 1, 42}, {960, 1, 7},
> -	{1024, 1, 43}, {1088, 22, 7}, {1152, 1, 8}, {1216, 43, 7}, {1280, 1, 9},
> -	{1408, 22, 9}, {1536, 1, 10}, {1664, 22, 10}, {1792, 1, 46},
> -	{1920, 1, 11}, {2048, 1, 47}, {2176, 43, 11}, {2304, 1, 12},
> -	{2560, 1, 13}, {2816, 43, 13}, {3072, 1, 14}, {3328, 43, 14},
> -	{3584, 1, 50}, {3840, 1, 15}, {4096, 1, 51}, {4608, 1, 16},
> -	{5120, 1, 17}, {6144, 1, 18}, {7168, 1, 54}, {7680, 1, 19},
> -	{8192, 1, 55}, {9216, 1, 20}, {10240, 1, 21}, {12288, 1, 22},
> -	{14336, 1, 58}, {15360, 1, 23}, {16384, 1, 59}, {18432, 1, 24},
> -	{20480, 1, 25}, {24576, 1, 26}, {28672, 1, 62}, {30720, 1, 27},
> -	{32768, 1, 63}, {36864, 1, 28}, {40960, 1, 29}, {49152, 1, 30},
> -	{61440, 1, 31}, {-1, 1, 31}
> -#elif defined(__M68K__)
> +#ifdef __M68K__
>  	{20, 32}, {22, 33}, {24, 34}, {26, 35},
>  	{28, 0}, {28, 36}, {30, 1}, {32, 37},
>  	{34, 2}, {36, 38}, {40, 3}, {40, 39},
> @@ -158,7 +138,6 @@ static unsigned int set_i2c_bus_speed(const struct fsl_i2c *dev,
>  	unsigned int i2c_clk, unsigned int speed)
>  {
>  	unsigned short divider = min(i2c_clk / speed, (unsigned short) -1);
> -	unsigned int i;
>  
>  	/*
>  	 * We want to choose an FDR/DFSR that generates an I2C bus speed that
> @@ -166,31 +145,72 @@ static unsigned int set_i2c_bus_speed(const struct fsl_i2c *dev,
>  	 * want the first divider that is equal to or greater than the
>  	 * calculated divider.
>  	 */
> -
> -	for (i = 0; i < ARRAY_SIZE(fsl_i2c_speed_map); i++)
> -		if (fsl_i2c_speed_map[i].divider >= divider) {
> -			u8 fdr;
>  #ifdef __PPC__
> -			u8 dfsr;
> +	u8 dfsr, fdr = 0x31; /* Default if no FDR found */
> +	/* a, b and dfsr matches identifiers A,B and C respectively in AN2919 */
> +	unsigned short a, b, ga, gb;
> +	unsigned long c_div, est_div;
> +
>  #ifdef CONFIG_FSL_I2C_CUSTOM_DFSR
> -			dfsr = CONFIG_FSL_I2C_CUSTOM_DFSR;
> +	dfsr = CONFIG_FSL_I2C_CUSTOM_DFSR;
>  #else
> -			dfsr = fsl_i2c_speed_map[i].dfsr;
> -#endif
> -			writeb(dfsr, &dev->dfsrr);	/* set default filter */
> +	/* Condition 1: dfsr <= 50/T */
> +	dfsr = (5 * (i2c_clk / 1000)) / 100000;
>  #endif
>  #ifdef CONFIG_FSL_I2C_CUSTOM_FDR
> -			fdr = CONFIG_FSL_I2C_CUSTOM_FDR;
> -			speed = i2c_clk / divider; /* Fake something */
> +	fdr = CONFIG_FSL_I2C_CUSTOM_FDR;
> +	speed = i2c_clk / divider; /* Fake something */
>  #else
> +	debug("Requested speed:%d, i2c_clk:%d\n", speed, i2c_clk);
> +	if (!dfsr)
> +		dfsr = 1;
> +
> +	est_div = ~0;
> +	for (ga = 0x4, a = 10; a <= 30; ga++, a += 2) {
> +		for (gb = 0; gb < 8; gb++) {
> +			b = 16 << gb;
> +			c_div = b * (a + ((3*dfsr)/b)*2);

Please use spaces around "/" and "*".

> +			if ((c_div > divider) && (c_div < est_div)) {
> +				unsigned short bin_gb, bin_ga;
> +
> +				est_div = c_div;
> +				bin_gb = gb << 2;
> +				bin_ga = (ga & 0x3) | ((ga & 0x4) << 3);
> +				fdr = bin_gb | bin_ga;
> +				speed = i2c_clk / est_div;
> +				debug("FDR:0x%.2x, div:%ld, ga:0x%x, gb:0x%x, "
> +				      "a:%d, b:%d, speed:%d\n",
> +				      fdr, est_div, ga, gb, a, b, speed);
> +				/* Condition 2 not accounted for */
> +				debug("Tr <= %d ns\n", 

Please remove trailing white space.

Wolfgang.