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 <[email protected]> > --- > 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 -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: [email protected] _______________________________________________ U-Boot mailing list [email protected] https://lists.denx.de/listinfo/u-boot
