[PATCH] i2c: exynos5: Calculate t_scl_l, t_scl_h according to i2c spec

[PATCH] i2c: exynos5: Calculate t_scl_l, t_scl_h according to i2c spec

[Camel Guo]

Previously the duty cycle was divided equally into h_scl_l, t_scl_h.
This makes the low period of the SCL clock in Fast Mode is only 1.25us
which is way lower than the minimal value (1.3) specified in i2c
specification. In order to make sure t_scl_l, t_scl_h always fullfill
i2c specification, this commit calculates t_scl_l using this formula:

t_scl_l = clk_cycle *
    ((t_low_min + (scl_clock - t_low_min - t_high_min) / 2) / scl_clock)

where:
t_low_min is the minimal value of low period of the SCL clock in us;
t_high_min is the minimal value of high period of the SCL clock in us;
scl_clock is converted from SCL clock frequency into us.

Signed-off-by: Camel Guo <camel.guo@axis.com>
---
 drivers/i2c/busses/i2c-exynos5.c | 34 +++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-exynos5.c b/drivers/i2c/busses/i2c-exynos5.c
index 4a6260d04db2..72bc8adea8d5 100644
--- a/drivers/i2c/busses/i2c-exynos5.c
+++ b/drivers/i2c/busses/i2c-exynos5.c
@@ -267,7 +267,7 @@ static void exynos5_i2c_clr_pend_irq(struct exynos5_i2c *i2c)
  * exynos5_i2c_set_timing: updates the registers with appropriate
  * timing values calculated
  *
- * Timing values for operation are calculated against either 100kHz
+ * Timing values for operation are calculated against 100kHz, 400kHz
  * or 1MHz controller operating frequency.
  *
  * Returns 0 on success, -EINVAL if the cycle length cannot
@@ -330,6 +330,23 @@ static int exynos5_i2c_set_timing(struct exynos5_i2c *i2c, bool hs_timings)
 	 *
 	 * Constraints: 4 <= temp, 0 <= CLK_DIV < 256, 2 <= clk_cycle <= 510
 	 *
+	 * To split SCL clock into low, high periods appropriately, one
+	 * proportion factor for each I2C mode is used, which is calculated
+	 * using this formula.
+	 * ```
+	 * ((t_low_min + (scl_clock - t_low_min - t_high_min) / 2) / scl_clock)
+	 * ```
+	 * where:
+	 * t_low_min is the minimal value of low period of the SCL clock in us;
+	 * t_high_min is the minimal value of high period of the SCL clock in us;
+	 * scl_clock is converted from SCL clock frequency into us.
+	 *
+	 * Below are the proportion factors for these I2C modes:
+	 *                t_low_min, t_high_min, scl_clock, proportion
+	 * Standard Mode:     4.7us,      4.0us,      10us,      0.535
+	 * Fast Mode:         1.3us,      0.6us,     2.5us,       0.64
+	 * Fast-Plus Mode:    0.5us,     0.26us,       1us,       0.62
+	 *
 	 */
 	t_ftl_cycle = (readl(i2c->regs + HSI2C_CONF) >> 16) & 0x7;
 	temp = clkin / op_clk - 8 - t_ftl_cycle;
@@ -343,8 +360,19 @@ static int exynos5_i2c_set_timing(struct exynos5_i2c *i2c, bool hs_timings)
 		return -EINVAL;
 	}
 
-	t_scl_l = clk_cycle / 2;
-	t_scl_h = clk_cycle / 2;
+	/*
+	 * Scale clk_cycle to get t_scl_l using the proption factors for individual I2C modes.
+	 */
+	if (op_clk <= I2C_MAX_STANDARD_MODE_FREQ)
+		t_scl_l = clk_cycle * 535 / 1000;
+	else if (op_clk <= I2C_MAX_FAST_MODE_FREQ)
+		t_scl_l = clk_cycle * 64 / 100;
+	else
+		t_scl_l = clk_cycle * 62 / 100;
+
+	if (t_scl_l > 0xFF)
+		t_scl_l = 0xFF;
+	t_scl_h = clk_cycle - t_scl_l;
 	t_start_su = t_scl_l;
 	t_start_hd = t_scl_l;
 	t_stop_su = t_scl_l;

base-commit: ce888220d5c7a805e0e155302a318d5d23e62950
-- 
2.30.2

Re: [PATCH] i2c: exynos5: Calculate t_scl_l, t_scl_h according to i2c spec

[Marek Szyprowski]

On 12.09.2022 10:59, Camel Guo wrote:
> Previously the duty cycle was divided equally into h_scl_l, t_scl_h.
> This makes the low period of the SCL clock in Fast Mode is only 1.25us
> which is way lower than the minimal value (1.3) specified in i2c
> specification. In order to make sure t_scl_l, t_scl_h always fullfill
> i2c specification, this commit calculates t_scl_l using this formula:
>
> t_scl_l = clk_cycle *
>      ((t_low_min + (scl_clock - t_low_min - t_high_min) / 2) / scl_clock)
>
> where:
> t_low_min is the minimal value of low period of the SCL clock in us;
> t_high_min is the minimal value of high period of the SCL clock in us;
> scl_clock is converted from SCL clock frequency into us.
>
> Signed-off-by: Camel Guo <camel.guo@axis.com>


This sounds reasonable and works fine on all Exynos-based test board I 
have. Feel free to add:

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>


> ---
>   drivers/i2c/busses/i2c-exynos5.c | 34 +++++++++++++++++++++++++++++---
>   1 file changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-exynos5.c b/drivers/i2c/busses/i2c-exynos5.c
> index 4a6260d04db2..72bc8adea8d5 100644
> --- a/drivers/i2c/busses/i2c-exynos5.c
> +++ b/drivers/i2c/busses/i2c-exynos5.c
> @@ -267,7 +267,7 @@ static void exynos5_i2c_clr_pend_irq(struct exynos5_i2c *i2c)
>    * exynos5_i2c_set_timing: updates the registers with appropriate
>    * timing values calculated
>    *
> - * Timing values for operation are calculated against either 100kHz
> + * Timing values for operation are calculated against 100kHz, 400kHz
>    * or 1MHz controller operating frequency.
>    *
>    * Returns 0 on success, -EINVAL if the cycle length cannot
> @@ -330,6 +330,23 @@ static int exynos5_i2c_set_timing(struct exynos5_i2c *i2c, bool hs_timings)
>   	 *
>   	 * Constraints: 4 <= temp, 0 <= CLK_DIV < 256, 2 <= clk_cycle <= 510
>   	 *
> +	 * To split SCL clock into low, high periods appropriately, one
> +	 * proportion factor for each I2C mode is used, which is calculated
> +	 * using this formula.
> +	 * ```
> +	 * ((t_low_min + (scl_clock - t_low_min - t_high_min) / 2) / scl_clock)
> +	 * ```
> +	 * where:
> +	 * t_low_min is the minimal value of low period of the SCL clock in us;
> +	 * t_high_min is the minimal value of high period of the SCL clock in us;
> +	 * scl_clock is converted from SCL clock frequency into us.
> +	 *
> +	 * Below are the proportion factors for these I2C modes:
> +	 *                t_low_min, t_high_min, scl_clock, proportion
> +	 * Standard Mode:     4.7us,      4.0us,      10us,      0.535
> +	 * Fast Mode:         1.3us,      0.6us,     2.5us,       0.64
> +	 * Fast-Plus Mode:    0.5us,     0.26us,       1us,       0.62
> +	 *
>   	 */
>   	t_ftl_cycle = (readl(i2c->regs + HSI2C_CONF) >> 16) & 0x7;
>   	temp = clkin / op_clk - 8 - t_ftl_cycle;
> @@ -343,8 +360,19 @@ static int exynos5_i2c_set_timing(struct exynos5_i2c *i2c, bool hs_timings)
>   		return -EINVAL;
>   	}
>   
> -	t_scl_l = clk_cycle / 2;
> -	t_scl_h = clk_cycle / 2;
> +	/*
> +	 * Scale clk_cycle to get t_scl_l using the proption factors for individual I2C modes.
> +	 */
> +	if (op_clk <= I2C_MAX_STANDARD_MODE_FREQ)
> +		t_scl_l = clk_cycle * 535 / 1000;
> +	else if (op_clk <= I2C_MAX_FAST_MODE_FREQ)
> +		t_scl_l = clk_cycle * 64 / 100;
> +	else
> +		t_scl_l = clk_cycle * 62 / 100;
> +
> +	if (t_scl_l > 0xFF)
> +		t_scl_l = 0xFF;
> +	t_scl_h = clk_cycle - t_scl_l;
>   	t_start_su = t_scl_l;
>   	t_start_hd = t_scl_l;
>   	t_stop_su = t_scl_l;
>
> base-commit: ce888220d5c7a805e0e155302a318d5d23e62950

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [PATCH] i2c: exynos5: Calculate t_scl_l, t_scl_h according to i2c spec

[Jesper Nilsson]

Thanks Marek for testing. We have been running with this patch for more
than a year now.

The patch has been orphaned for 6 months as Camel no longer works here,
but since I was involved in the creation of it I can resend it.

/Jesper

On Mon, Oct 23, 2023 at 12:34:19PM +0200, Marek Szyprowski wrote:
> On 12.09.2022 10:59, Camel Guo wrote:
> > Previously the duty cycle was divided equally into h_scl_l, t_scl_h.
> > This makes the low period of the SCL clock in Fast Mode is only 1.25us
> > which is way lower than the minimal value (1.3) specified in i2c
> > specification. In order to make sure t_scl_l, t_scl_h always fullfill
> > i2c specification, this commit calculates t_scl_l using this formula:
> >
> > t_scl_l = clk_cycle *
> >      ((t_low_min + (scl_clock - t_low_min - t_high_min) / 2) / scl_clock)
> >
> > where:
> > t_low_min is the minimal value of low period of the SCL clock in us;
> > t_high_min is the minimal value of high period of the SCL clock in us;
> > scl_clock is converted from SCL clock frequency into us.
> >
> > Signed-off-by: Camel Guo <camel.guo@axis.com>
> 
> 
> This sounds reasonable and works fine on all Exynos-based test board I 
> have. Feel free to add:
> 
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> 
> Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
> 
> 
> > ---
> >   drivers/i2c/busses/i2c-exynos5.c | 34 +++++++++++++++++++++++++++++---
> >   1 file changed, 31 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-exynos5.c b/drivers/i2c/busses/i2c-exynos5.c
> > index 4a6260d04db2..72bc8adea8d5 100644
> > --- a/drivers/i2c/busses/i2c-exynos5.c
> > +++ b/drivers/i2c/busses/i2c-exynos5.c
> > @@ -267,7 +267,7 @@ static void exynos5_i2c_clr_pend_irq(struct exynos5_i2c *i2c)
> >    * exynos5_i2c_set_timing: updates the registers with appropriate
> >    * timing values calculated
> >    *
> > - * Timing values for operation are calculated against either 100kHz
> > + * Timing values for operation are calculated against 100kHz, 400kHz
> >    * or 1MHz controller operating frequency.
> >    *
> >    * Returns 0 on success, -EINVAL if the cycle length cannot
> > @@ -330,6 +330,23 @@ static int exynos5_i2c_set_timing(struct exynos5_i2c *i2c, bool hs_timings)
> >   	 *
> >   	 * Constraints: 4 <= temp, 0 <= CLK_DIV < 256, 2 <= clk_cycle <= 510
> >   	 *
> > +	 * To split SCL clock into low, high periods appropriately, one
> > +	 * proportion factor for each I2C mode is used, which is calculated
> > +	 * using this formula.
> > +	 * ```
> > +	 * ((t_low_min + (scl_clock - t_low_min - t_high_min) / 2) / scl_clock)
> > +	 * ```
> > +	 * where:
> > +	 * t_low_min is the minimal value of low period of the SCL clock in us;
> > +	 * t_high_min is the minimal value of high period of the SCL clock in us;
> > +	 * scl_clock is converted from SCL clock frequency into us.
> > +	 *
> > +	 * Below are the proportion factors for these I2C modes:
> > +	 *                t_low_min, t_high_min, scl_clock, proportion
> > +	 * Standard Mode:     4.7us,      4.0us,      10us,      0.535
> > +	 * Fast Mode:         1.3us,      0.6us,     2.5us,       0.64
> > +	 * Fast-Plus Mode:    0.5us,     0.26us,       1us,       0.62
> > +	 *
> >   	 */
> >   	t_ftl_cycle = (readl(i2c->regs + HSI2C_CONF) >> 16) & 0x7;
> >   	temp = clkin / op_clk - 8 - t_ftl_cycle;
> > @@ -343,8 +360,19 @@ static int exynos5_i2c_set_timing(struct exynos5_i2c *i2c, bool hs_timings)
> >   		return -EINVAL;
> >   	}
> >   
> > -	t_scl_l = clk_cycle / 2;
> > -	t_scl_h = clk_cycle / 2;
> > +	/*
> > +	 * Scale clk_cycle to get t_scl_l using the proption factors for individual I2C modes.
> > +	 */
> > +	if (op_clk <= I2C_MAX_STANDARD_MODE_FREQ)
> > +		t_scl_l = clk_cycle * 535 / 1000;
> > +	else if (op_clk <= I2C_MAX_FAST_MODE_FREQ)
> > +		t_scl_l = clk_cycle * 64 / 100;
> > +	else
> > +		t_scl_l = clk_cycle * 62 / 100;
> > +
> > +	if (t_scl_l > 0xFF)
> > +		t_scl_l = 0xFF;
> > +	t_scl_h = clk_cycle - t_scl_l;
> >   	t_start_su = t_scl_l;
> >   	t_start_hd = t_scl_l;
> >   	t_stop_su = t_scl_l;
> >
> > base-commit: ce888220d5c7a805e0e155302a318d5d23e62950
> 
> Best regards
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland

/^JN - Jesper Nilsson
-- 
               Jesper Nilsson -- jesper.nilsson@axis.com

Re: [PATCH] i2c: exynos5: Calculate t_scl_l, t_scl_h according to i2c spec

[Wolfram Sang]

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On Mon, Oct 23, 2023 at 04:06:27PM +0200, Jesper Nilsson wrote:
> Thanks Marek for testing. We have been running with this patch for more
> than a year now.
> 
> The patch has been orphaned for 6 months as Camel no longer works here,
> but since I was involved in the creation of it I can resend it.

No need. It still applies :)


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Re: [PATCH] i2c: exynos5: Calculate t_scl_l, t_scl_h according to i2c spec

[Wolfram Sang]

[-- Attachment #1: Type: text/plain, Size: 832 bytes --]

On Mon, Sep 12, 2022 at 10:59:43AM +0200, Camel Guo wrote:
> Previously the duty cycle was divided equally into h_scl_l, t_scl_h.
> This makes the low period of the SCL clock in Fast Mode is only 1.25us
> which is way lower than the minimal value (1.3) specified in i2c
> specification. In order to make sure t_scl_l, t_scl_h always fullfill
> i2c specification, this commit calculates t_scl_l using this formula:
> 
> t_scl_l = clk_cycle *
>     ((t_low_min + (scl_clock - t_low_min - t_high_min) / 2) / scl_clock)
> 
> where:
> t_low_min is the minimal value of low period of the SCL clock in us;
> t_high_min is the minimal value of high period of the SCL clock in us;
> scl_clock is converted from SCL clock frequency into us.
> 
> Signed-off-by: Camel Guo <camel.guo@axis.com>

Applied to for-next, thanks!


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