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

Lukasz Majewski
2017-03-27T08:04:53Z

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@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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