Re: [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 
---
  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: w...@denx.de



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HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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Re: [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 
> ---
>  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: w...@denx.de
___
U-Boot mailing list
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[U-Boot] [PATCH 2/2] i2c: ti: Update method to calculate psc, sscl and ssch I2C parameters

[Lukasz Majewski]

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

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 
---
 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;
 }
 
 /*
-- 
2.1.4

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