[PATCH 1/2] I2C: OMAP2/3: Fix scll/sclh calculations

[PATCH 1/2] I2C: OMAP2/3: Fix scll/sclh calculations

[Aaro Koskinen]

Fix scll/sclh calculations for HS and fast modes. Currently the driver
uses equal (roughly) low/high times which will result in too short
low time.

OMAP3430 TRM gives the following equations:

	F/S: tLow  = (scll + 7) * internal_clk
	     tHigh = (sclh + 5) * internal_clk
	HS:  tLow  = (scll + 7) * fclk
	     tHigh = (sclh + 5) * fclk

Furthermore, the I2C specification sets the following minimum values
for HS tLow/tHigh for capacitive bus loads 100 pF (maximum speed 3400)
and 400 pF (maximum speed 1700):

	speed	tLow		tHigh
	3400	160 ns		60 ns
	1700	320 ns		120 ns

and for F/S:

	speed	tLow		tHigh
	400	1300 ns		600 ns
	100	4700 ns		4000 ns

By using duty cycles 33/66 (HS, F) and 50/50 (S) we stay above these
minimum values.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
---
 drivers/i2c/busses/i2c-omap.c |   25 ++++++++++++++++++-------
 1 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index 9919c08..5d9880c 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -343,17 +343,28 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
 
 		/* If configured for High Speed */
 		if (dev->speed > 400) {
+			unsigned long scl;
+
 			/* For first phase of HS mode */
-			fsscll = internal_clk / (400 * 2) - 6;
-			fssclh = internal_clk / (400 * 2) - 6;
+			scl = internal_clk / 400;
+			fsscll = scl - (scl / 3) - 7;
+			fssclh = (scl / 3) - 5;
 
 			/* For second phase of HS mode */
-			hsscll = fclk_rate / (dev->speed * 2) - 6;
-			hssclh = fclk_rate / (dev->speed * 2) - 6;
+			scl = fclk_rate / dev->speed;
+			hsscll = scl - (scl / 3) - 7;
+			hssclh = (scl / 3) - 5;
+		} else if (dev->speed > 100) {
+			unsigned long scl;
+
+			/* Fast mode */
+			scl = internal_clk / dev->speed;
+			fsscll = scl - (scl / 3) - 7;
+			fssclh = (scl / 3) - 5;
 		} else {
-			/* To handle F/S modes */
-			fsscll = internal_clk / (dev->speed * 2) - 6;
-			fssclh = internal_clk / (dev->speed * 2) - 6;
+			/* Standard mode */
+			fsscll = internal_clk / (dev->speed * 2) - 7;
+			fssclh = internal_clk / (dev->speed * 2) - 5;
 		}
 		scll = (hsscll << OMAP_I2C_SCLL_HSSCLL) | fsscll;
 		sclh = (hssclh << OMAP_I2C_SCLH_HSSCLH) | fssclh;
-- 
1.5.4.3

[PATCH 2/2] I2C: OMAP3: Better noise suppression for fast/standard modes

[Aaro Koskinen]

Use longer noise filter period for fast and standard mode. Based on an
earlier patch by Eero Nurkkala.

Signed-off-by: Aaro Koskinen <aaro.koskinen-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>
---
 drivers/i2c/busses/i2c-omap.c |   14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index 5d9880c..8c76cea 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -333,8 +333,18 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
 
 	if (cpu_is_omap2430() || cpu_is_omap34xx()) {
 
-		/* HSI2C controller internal clk rate should be 19.2 Mhz */
-		internal_clk = 19200;
+		/*
+		 * HSI2C controller internal clk rate should be 19.2 Mhz for
+		 * HS and for all modes on 2430. On 34xx we can use lower rate
+		 * to get longer filter period for better noise suppression.
+		 * The filter is iclk (fclk for HS) period.
+		 */
+		if (dev->speed > 400 || cpu_is_omap_2430())
+			internal_clk = 19200;
+		else if (dev->speed > 100)
+			internal_clk = 9600;
+		else
+			internal_clk = 4000;
 		fclk_rate = clk_get_rate(dev->fclk) / 1000;
 
 		/* Compute prescaler divisor */
-- 
1.5.4.3

Re: [PATCH 2/2] I2C: OMAP3: Better noise suppression for fast/standard modes

[Tony Lindgren]

* Aaro Koskinen <aaro.koskinen@nokia.com> [090527 07:55]:
> Use longer noise filter period for fast and standard mode. Based on an
> earlier patch by Eero Nurkkala.
> 
> Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>

Ben this should be queued too.

Acked-by: Tony Lindgren <tony@atomide.com>

> ---
>  drivers/i2c/busses/i2c-omap.c |   14 ++++++++++++--
>  1 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index 5d9880c..8c76cea 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -333,8 +333,18 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
>  
>  	if (cpu_is_omap2430() || cpu_is_omap34xx()) {
>  
> -		/* HSI2C controller internal clk rate should be 19.2 Mhz */
> -		internal_clk = 19200;
> +		/*
> +		 * HSI2C controller internal clk rate should be 19.2 Mhz for
> +		 * HS and for all modes on 2430. On 34xx we can use lower rate
> +		 * to get longer filter period for better noise suppression.
> +		 * The filter is iclk (fclk for HS) period.
> +		 */
> +		if (dev->speed > 400 || cpu_is_omap_2430())
> +			internal_clk = 19200;
> +		else if (dev->speed > 100)
> +			internal_clk = 9600;
> +		else
> +			internal_clk = 4000;
>  		fclk_rate = clk_get_rate(dev->fclk) / 1000;
>  
>  		/* Compute prescaler divisor */
> -- 
> 1.5.4.3
> 
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Re: [PATCH 1/2] I2C: OMAP2/3: Fix scll/sclh calculations

[Tony Lindgren]

* Aaro Koskinen <aaro.koskinen-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org> [090527 07:55]:
> Fix scll/sclh calculations for HS and fast modes. Currently the driver
> uses equal (roughly) low/high times which will result in too short
> low time.
> 
> OMAP3430 TRM gives the following equations:
> 
> 	F/S: tLow  = (scll + 7) * internal_clk
> 	     tHigh = (sclh + 5) * internal_clk
> 	HS:  tLow  = (scll + 7) * fclk
> 	     tHigh = (sclh + 5) * fclk
> 
> Furthermore, the I2C specification sets the following minimum values
> for HS tLow/tHigh for capacitive bus loads 100 pF (maximum speed 3400)
> and 400 pF (maximum speed 1700):
> 
> 	speed	tLow		tHigh
> 	3400	160 ns		60 ns
> 	1700	320 ns		120 ns
> 
> and for F/S:
> 
> 	speed	tLow		tHigh
> 	400	1300 ns		600 ns
> 	100	4700 ns		4000 ns
> 
> By using duty cycles 33/66 (HS, F) and 50/50 (S) we stay above these
> minimum values.
> 
> Signed-off-by: Aaro Koskinen <aaro.koskinen-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>

Ben can you please queue this?

Acked-by: Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>

> ---
>  drivers/i2c/busses/i2c-omap.c |   25 ++++++++++++++++++-------
>  1 files changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index 9919c08..5d9880c 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -343,17 +343,28 @@ static int omap_i2c_init(struct omap_i2c_dev *dev)
>  
>  		/* If configured for High Speed */
>  		if (dev->speed > 400) {
> +			unsigned long scl;
> +
>  			/* For first phase of HS mode */
> -			fsscll = internal_clk / (400 * 2) - 6;
> -			fssclh = internal_clk / (400 * 2) - 6;
> +			scl = internal_clk / 400;
> +			fsscll = scl - (scl / 3) - 7;
> +			fssclh = (scl / 3) - 5;
>  
>  			/* For second phase of HS mode */
> -			hsscll = fclk_rate / (dev->speed * 2) - 6;
> -			hssclh = fclk_rate / (dev->speed * 2) - 6;
> +			scl = fclk_rate / dev->speed;
> +			hsscll = scl - (scl / 3) - 7;
> +			hssclh = (scl / 3) - 5;
> +		} else if (dev->speed > 100) {
> +			unsigned long scl;
> +
> +			/* Fast mode */
> +			scl = internal_clk / dev->speed;
> +			fsscll = scl - (scl / 3) - 7;
> +			fssclh = (scl / 3) - 5;
>  		} else {
> -			/* To handle F/S modes */
> -			fsscll = internal_clk / (dev->speed * 2) - 6;
> -			fssclh = internal_clk / (dev->speed * 2) - 6;
> +			/* Standard mode */
> +			fsscll = internal_clk / (dev->speed * 2) - 7;
> +			fssclh = internal_clk / (dev->speed * 2) - 5;
>  		}
>  		scll = (hsscll << OMAP_I2C_SCLL_HSSCLL) | fsscll;
>  		sclh = (hssclh << OMAP_I2C_SCLH_HSSCLH) | fssclh;
> -- 
> 1.5.4.3
> 
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