[U-Boot] [PATCH 2/2] i2c: ti: Update method to calculate psc, sscl and ssch I2C parameters

[Lukasz Majewski]

Dear All,

> This patch updates the way in which psc, sscl and ssch I2C parameters
> are calculated to be in sync with v4.9 Linux kernel
> SHA1: 69973b830859bc6529a7a0468ba0d80ee5117826
> in the ./drivers/i2c/busses/i2c-omap.c

Any comments on this?

> 
> The previous method was causing several issues:
> - The internal I2C frequency (after prescaler) was far above
> recommended one (7 - 12 MHz [*]) - the current approach brings better
> noise suppression (as stated in Linux commit: SHA1:
> 84bf2c868f3ca996e5bb)
> 
> - The values calculated (psc, sscl and ssch) were far from optimal,
> which caused on the test platform (AM57xx) the I2C0 SCL signal low
> time (Fast Mode) of ~1.0us (the standard requires > 1.3 us).
> 
> [*] for AM57xx TRM SPRUHZ6G, Table 24,7
> "HS I2C Register Values for Maximum I2C Bit Rates in I2C F/S, I2C HS
> Modes"
> 
> Signed-off-by: Lukasz Majewski <lukma at denx.de>
> ---
>  drivers/i2c/omap24xx_i2c.c | 66
> ++++++++++++++++++++++++++++------------------ 1 file changed, 41
> insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/i2c/omap24xx_i2c.c b/drivers/i2c/omap24xx_i2c.c
> index 0006343..26996e9 100644
> --- a/drivers/i2c/omap24xx_i2c.c
> +++ b/drivers/i2c/omap24xx_i2c.c
> @@ -64,36 +64,52 @@ struct omap_i2c {
>  
>  static int omap24_i2c_findpsc(u32 *pscl, u32 *psch, uint speed)
>  {
> -	unsigned int sampleclk, prescaler;
> -	int fsscll, fssclh;
> +	unsigned long internal_clk = 0, fclk;
> +	unsigned int prescaler;
>  
> -	speed <<= 1;
> -	prescaler = 0;
>  	/*
> -	 * some divisors may cause a precission loss, but shouldn't
> -	 * be a big thing, because i2c_clk is then allready very
> slow.
> +	 * This method is only called for Standard and Fast Mode
> speeds
> +	 *
> +	 * For some TI SoCs it is explicitly written in TRM (e,g,
> SPRUHZ6G,
> +	 * page 5685, Table 24-7)
> +	 * that the internal I2C clock (after prescaler) should be
> between
> +	 * 7-12 MHz (at least for Fast Mode (FS)).
> +	 *
> +	 * Such approach is used in v4.9 Linux kernel in:
> +	 * ./drivers/i2c/busses/i2c-omap.c (omap_i2c_init function).
>  	 */
> -	while (prescaler <= 0xFF) {
> -		sampleclk = I2C_IP_CLK / (prescaler+1);
>  
> -		fsscll = sampleclk / speed;
> -		fssclh = fsscll;
> -		fsscll -= I2C_FASTSPEED_SCLL_TRIM;
> -		fssclh -= I2C_FASTSPEED_SCLH_TRIM;
> -
> -		if (((fsscll > 0) && (fssclh > 0)) &&
> -		    ((fsscll <= (255-I2C_FASTSPEED_SCLL_TRIM)) &&
> -		    (fssclh <= (255-I2C_FASTSPEED_SCLH_TRIM)))) {
> -			if (pscl)
> -				*pscl = fsscll;
> -			if (psch)
> -				*psch = fssclh;
> -
> -			return prescaler;
> -		}
> -		prescaler++;
> +	speed /= 1000; /* convert speed to kHz */
> +
> +	if (speed > 100)
> +		internal_clk = 9600;
> +	else
> +		internal_clk = 4000;
> +
> +	fclk = I2C_IP_CLK / 1000;
> +	prescaler = fclk / internal_clk;
> +	prescaler = prescaler - 1;
> +
> +	if (speed > 100) {
> +		unsigned long scl;
> +
> +		/* Fast mode */
> +		scl = internal_clk / speed;
> +		*pscl = scl - (scl / 3) - I2C_FASTSPEED_SCLL_TRIM;
> +		*psch = (scl / 3) - I2C_FASTSPEED_SCLH_TRIM;
> +	} else {
> +		/* Standard mode */
> +		*pscl = internal_clk / (speed * 2) -
> I2C_FASTSPEED_SCLL_TRIM;
> +		*psch = internal_clk / (speed * 2) -
> I2C_FASTSPEED_SCLH_TRIM; }
> -	return -1;
> +
> +	debug("%s: speed [kHz]: %d psc: 0x%x sscl: 0x%x ssch:
> 0x%x\n",
> +	      __func__, speed, prescaler, *pscl, *psch);
> +
> +	if (*pscl <= 0 || *psch <= 0 || prescaler <= 0)
> +		return -EINVAL;
> +
> +	return prescaler;
>  }
>  
>  /*




Best regards,

Lukasz Majewski

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