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

[Heiko Schocher]

Hello Lukasz,

Am 27.03.2017 um 10:04 schrieb 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?

I am fine with it, it is in my queue for sending a pull
request to Tom.

bye,
Heiko

>
>>
>> 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
>
> --
>
> 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: wd at denx.de
>

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany