[PATCH v2 0/2] Ensure High and Low periods of SCL are correct

[PATCH v2 0/2] Ensure High and Low periods of SCL are correct

[Lucas Tanure]

The default duty cycle of 33% is less than the required
by the I2C specs for the LOW period of the SCL clock at
100KHz bus speed.

So, for 100Khz or less, use 50%H/50%L duty cycle, and
for the clock above 100Khz, use 40%H/60%L duty cycle.
That ensures the low period of SCL is always more than
the minimum required by the specs at any given frequency.

I did a few measures on the Khadas Vim3 board:

i2c_AO (i2c@5000):

Before the patchset, I got:
- 100KHz: 3.338us HIGH, 6.746us LOW, 33%/67%, Freq 99KHz (Not Valid tHIGH < 4.0us)
- 400KHz: 860ns HIGH, 1.734us LOW, 33.15%/62.85%, Freq 385.505KHz (Valid)
- 1000KHz: 362ns HIGH, 732ns LOW, 33.09%/66.91%, Freq 914.077KHz (Valid)

With the patchset
- 100KHz: 4.952us HIGH, 5.134us LOW, 49%/51%, Freq 99KHz (Valid)
- 400KHz: 966ns HIGH, 1.628us LOW, 37.24%/62.76%, Freq 385.505KHz (Valid)
- 1000KHz: 372ns HIGH, 720ns LOW, 34.07%/65.93%, Freq 915.741KHz (Valid)

i2c3 (i2c@1c000):

Before the patchset, I got:
- 100KHz: 3.348us HIGH, 6.704us LOW, 33%/67%, Freq 99.5KHz (Not Valid tHIGH < 4.0us)
- 400KHz: 864ns HIGH, 1.69us LOW, 33.83%/62.17%, Freq 391.543KHz (Valid)
- 1000KHz: 360ns HIGH, 690ns LOW, 34.29%/65.71%, Freq 952.381KHz (Valid)

With the patchset
- 100KHz: 4.958us HIGH, 5.092us LOW, 49%/51%, Freq 99KHz (Valid)
- 400KHz: 970ns HIGH, 1.582us LOW, 38%/62%, Freq 391.85KHz (Valid)
- 1000KHz: 370ns HIGH, 680ns LOW, 35.24%/64.76%, Freq 952.57KHz (Valid)

v2 changelog:
 - Keep the previous calculation for Meson6
 - Use I2C_MAX_STANDARD_MODE_FREQ
 - move the comment before the if()
 - use FIELD_PREP for setting div_l
 - Drop removal of meson_i2c_data

Previous versions:
 V1: https://lkml.org/lkml/2022/3/26/109

Lucas Tanure (2):
  i2c: meson: Use _SHIFT and _MASK for register definitions
  i2c: meson: Use 50% duty cycle for I2C clock

 drivers/i2c/busses/i2c-meson.c | 111 ++++++++++++++++++++++++---------
 1 file changed, 82 insertions(+), 29 deletions(-)

-- 
2.35.1

[PATCH v2 1/2] i2c: meson: Use _SHIFT and _MASK for register definitions

[Lucas Tanure]

Differentiate between masks and shifts

Signed-off-by: Lucas Tanure <tanure@linux.com>
---
 drivers/i2c/busses/i2c-meson.c | 41 ++++++++++++++++++----------------
 1 file changed, 22 insertions(+), 19 deletions(-)

diff --git a/drivers/i2c/busses/i2c-meson.c b/drivers/i2c/busses/i2c-meson.c
index 07eb819072c4..4b4a5b2d77ab 100644
--- a/drivers/i2c/busses/i2c-meson.c
+++ b/drivers/i2c/busses/i2c-meson.c
@@ -30,18 +30,21 @@
 #define REG_TOK_RDATA1		0x1c
 
 /* Control register fields */
-#define REG_CTRL_START		BIT(0)
-#define REG_CTRL_ACK_IGNORE	BIT(1)
-#define REG_CTRL_STATUS		BIT(2)
-#define REG_CTRL_ERROR		BIT(3)
-#define REG_CTRL_CLKDIV		GENMASK(21, 12)
-#define REG_CTRL_CLKDIVEXT	GENMASK(29, 28)
-
-#define REG_SLV_ADDR		GENMASK(7, 0)
-#define REG_SLV_SDA_FILTER	GENMASK(10, 8)
-#define REG_SLV_SCL_FILTER	GENMASK(13, 11)
-#define REG_SLV_SCL_LOW		GENMASK(27, 16)
-#define REG_SLV_SCL_LOW_EN	BIT(28)
+#define REG_CTRL_START			BIT(0)
+#define REG_CTRL_ACK_IGNORE		BIT(1)
+#define REG_CTRL_STATUS			BIT(2)
+#define REG_CTRL_ERROR			BIT(3)
+#define REG_CTRL_CLKDIV_SHIFT		12
+#define REG_CTRL_CLKDIV_MASK		GENMASK(21, REG_CTRL_CLKDIV_SHIFT)
+#define REG_CTRL_CLKDIVEXT_SHIFT	28
+#define REG_CTRL_CLKDIVEXT_MASK		GENMASK(29, REG_CTRL_CLKDIVEXT_SHIFT)
+
+#define REG_SLV_ADDR_MASK		GENMASK(7, 0)
+#define REG_SLV_SDA_FILTER_MASK		GENMASK(10, 8)
+#define REG_SLV_SCL_FILTER_MASK		GENMASK(13, 11)
+#define REG_SLV_SCL_LOW_SHIFT		16
+#define REG_SLV_SCL_LOW_MASK		GENMASK(27, REG_SLV_SCL_LOW_SHIFT)
+#define REG_SLV_SCL_LOW_EN		BIT(28)
 
 #define I2C_TIMEOUT_MS		500
 #define FILTER_DELAY		15
@@ -149,11 +152,11 @@ static void meson_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
 		div = GENMASK(11, 0);
 	}
 
-	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV,
-			   FIELD_PREP(REG_CTRL_CLKDIV, div & GENMASK(9, 0)));
+	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV_MASK,
+			   FIELD_PREP(REG_CTRL_CLKDIV_MASK, div & GENMASK(9, 0)));
 
-	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT,
-			   FIELD_PREP(REG_CTRL_CLKDIVEXT, div >> 10));
+	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT_MASK,
+			   FIELD_PREP(REG_CTRL_CLKDIVEXT_MASK, div >> 10));
 
 	/* Disable HIGH/LOW mode */
 	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_EN, 0);
@@ -292,8 +295,8 @@ static void meson_i2c_do_start(struct meson_i2c *i2c, struct i2c_msg *msg)
 		TOKEN_SLAVE_ADDR_WRITE;
 
 
-	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_ADDR,
-			   FIELD_PREP(REG_SLV_ADDR, msg->addr << 1));
+	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_ADDR_MASK,
+			   FIELD_PREP(REG_SLV_ADDR_MASK, msg->addr << 1));
 
 	meson_i2c_add_token(i2c, TOKEN_START);
 	meson_i2c_add_token(i2c, token);
@@ -467,7 +470,7 @@ static int meson_i2c_probe(struct platform_device *pdev)
 
 	/* Disable filtering */
 	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR,
-			   REG_SLV_SDA_FILTER | REG_SLV_SCL_FILTER, 0);
+			   REG_SLV_SDA_FILTER_MASK | REG_SLV_SCL_FILTER_MASK, 0);
 
 	meson_i2c_set_clk_div(i2c, timings.bus_freq_hz);
 
-- 
2.35.1

Re: [PATCH v2 1/2] i2c: meson: Use _SHIFT and _MASK for register definitions

[Neil Armstrong]

On 09/04/2022 18:43, Lucas Tanure wrote:
> Differentiate between masks and shifts
> 
> Signed-off-by: Lucas Tanure <tanure@linux.com>
> ---
>   drivers/i2c/busses/i2c-meson.c | 41 ++++++++++++++++++----------------
>   1 file changed, 22 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-meson.c b/drivers/i2c/busses/i2c-meson.c
> index 07eb819072c4..4b4a5b2d77ab 100644
> --- a/drivers/i2c/busses/i2c-meson.c
> +++ b/drivers/i2c/busses/i2c-meson.c
> @@ -30,18 +30,21 @@
>   #define REG_TOK_RDATA1		0x1c
>   
>   /* Control register fields */
> -#define REG_CTRL_START		BIT(0)
> -#define REG_CTRL_ACK_IGNORE	BIT(1)
> -#define REG_CTRL_STATUS		BIT(2)
> -#define REG_CTRL_ERROR		BIT(3)
> -#define REG_CTRL_CLKDIV		GENMASK(21, 12)
> -#define REG_CTRL_CLKDIVEXT	GENMASK(29, 28)
> -
> -#define REG_SLV_ADDR		GENMASK(7, 0)
> -#define REG_SLV_SDA_FILTER	GENMASK(10, 8)
> -#define REG_SLV_SCL_FILTER	GENMASK(13, 11)
> -#define REG_SLV_SCL_LOW		GENMASK(27, 16)
> -#define REG_SLV_SCL_LOW_EN	BIT(28)
> +#define REG_CTRL_START			BIT(0)
> +#define REG_CTRL_ACK_IGNORE		BIT(1)
> +#define REG_CTRL_STATUS			BIT(2)
> +#define REG_CTRL_ERROR			BIT(3)
> +#define REG_CTRL_CLKDIV_SHIFT		12
> +#define REG_CTRL_CLKDIV_MASK		GENMASK(21, REG_CTRL_CLKDIV_SHIFT)
> +#define REG_CTRL_CLKDIVEXT_SHIFT	28
> +#define REG_CTRL_CLKDIVEXT_MASK		GENMASK(29, REG_CTRL_CLKDIVEXT_SHIFT)
> +
> +#define REG_SLV_ADDR_MASK		GENMASK(7, 0)
> +#define REG_SLV_SDA_FILTER_MASK		GENMASK(10, 8)
> +#define REG_SLV_SCL_FILTER_MASK		GENMASK(13, 11)
> +#define REG_SLV_SCL_LOW_SHIFT		16
> +#define REG_SLV_SCL_LOW_MASK		GENMASK(27, REG_SLV_SCL_LOW_SHIFT)
> +#define REG_SLV_SCL_LOW_EN		BIT(28)
>   
>   #define I2C_TIMEOUT_MS		500
>   #define FILTER_DELAY		15
> @@ -149,11 +152,11 @@ static void meson_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
>   		div = GENMASK(11, 0);
>   	}
>   
> -	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV,
> -			   FIELD_PREP(REG_CTRL_CLKDIV, div & GENMASK(9, 0)));
> +	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV_MASK,
> +			   FIELD_PREP(REG_CTRL_CLKDIV_MASK, div & GENMASK(9, 0)));
>   
> -	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT,
> -			   FIELD_PREP(REG_CTRL_CLKDIVEXT, div >> 10));
> +	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT_MASK,
> +			   FIELD_PREP(REG_CTRL_CLKDIVEXT_MASK, div >> 10));
>   
>   	/* Disable HIGH/LOW mode */
>   	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_EN, 0);
> @@ -292,8 +295,8 @@ static void meson_i2c_do_start(struct meson_i2c *i2c, struct i2c_msg *msg)
>   		TOKEN_SLAVE_ADDR_WRITE;
>   
>   
> -	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_ADDR,
> -			   FIELD_PREP(REG_SLV_ADDR, msg->addr << 1));
> +	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_ADDR_MASK,
> +			   FIELD_PREP(REG_SLV_ADDR_MASK, msg->addr << 1));
>   
>   	meson_i2c_add_token(i2c, TOKEN_START);
>   	meson_i2c_add_token(i2c, token);
> @@ -467,7 +470,7 @@ static int meson_i2c_probe(struct platform_device *pdev)
>   
>   	/* Disable filtering */
>   	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR,
> -			   REG_SLV_SDA_FILTER | REG_SLV_SCL_FILTER, 0);
> +			   REG_SLV_SDA_FILTER_MASK | REG_SLV_SCL_FILTER_MASK, 0);
>   
>   	meson_i2c_set_clk_div(i2c, timings.bus_freq_hz);
>   

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>

Re: [PATCH v2 1/2] i2c: meson: Use _SHIFT and _MASK for register definitions

[Wolfram Sang]

[-- Attachment #1: Type: text/plain, Size: 193 bytes --]

On Sat, Apr 09, 2022 at 05:43:33PM +0100, Lucas Tanure wrote:
> Differentiate between masks and shifts
> 
> Signed-off-by: Lucas Tanure <tanure@linux.com>

Applied to for-next, thanks!


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[PATCH v2 2/2] i2c: meson: Use 50% duty cycle for I2C clock

[Lucas Tanure]

The duty cycle of 33% is less than the required
by the I2C specs for the LOW period of the SCL
clock.

Move the duty cyle to 50% for 100Khz or lower
clocks, and (40% High SCL / 60% Low SCL) duty
cycle for clocks above 100Khz.

Signed-off-by: Lucas Tanure <tanure@linux.com>
---
 drivers/i2c/busses/i2c-meson.c | 70 +++++++++++++++++++++++++++++-----
 1 file changed, 60 insertions(+), 10 deletions(-)

diff --git a/drivers/i2c/busses/i2c-meson.c b/drivers/i2c/busses/i2c-meson.c
index 4b4a5b2d77ab..50dab123380a 100644
--- a/drivers/i2c/busses/i2c-meson.c
+++ b/drivers/i2c/busses/i2c-meson.c
@@ -65,10 +65,6 @@ enum {
 	STATE_WRITE,
 };
 
-struct meson_i2c_data {
-	unsigned char div_factor;
-};
-
 /**
  * struct meson_i2c - Meson I2C device private data
  *
@@ -109,6 +105,10 @@ struct meson_i2c {
 	const struct meson_i2c_data *data;
 };
 
+struct meson_i2c_data {
+	void (*set_clk_div)(struct meson_i2c *i2c, unsigned int freq);
+};
+
 static void meson_i2c_set_mask(struct meson_i2c *i2c, int reg, u32 mask,
 			       u32 val)
 {
@@ -137,14 +137,62 @@ static void meson_i2c_add_token(struct meson_i2c *i2c, int token)
 	i2c->num_tokens++;
 }
 
-static void meson_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
+static void meson_gxbb_axg_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
+{
+	unsigned long clk_rate = clk_get_rate(i2c->clk);
+	unsigned int div_h, div_l;
+
+	/* According to I2C-BUS Spec 2.1, in FAST-MODE, the minimum LOW period is 1.3uS, and
+	 * minimum HIGH is least 0.6us.
+	 * For 400000 freq, the period is 2.5us. To keep within the specs, give 40% of period to
+	 * HIGH and 60% to LOW. This means HIGH at 1.0us and LOW 1.5us.
+	 * The same applies for Fast-mode plus, where LOW is 0.5us and HIGH is 0.26us.
+	 * Duty = H/(H + L) = 2/5
+	 */
+	if (freq <= I2C_MAX_STANDARD_MODE_FREQ) {
+		div_h = DIV_ROUND_UP(clk_rate, freq);
+		div_l = DIV_ROUND_UP(div_h, 4);
+		div_h = DIV_ROUND_UP(div_h, 2) - FILTER_DELAY;
+	} else {
+		div_h = DIV_ROUND_UP(clk_rate * 2, freq * 5) - FILTER_DELAY;
+		div_l = DIV_ROUND_UP(clk_rate * 3, freq * 5 * 2);
+	}
+
+	/* clock divider has 12 bits */
+	if (div_h > GENMASK(11, 0)) {
+		dev_err(i2c->dev, "requested bus frequency too low\n");
+		div_h = GENMASK(11, 0);
+	}
+	if (div_l > GENMASK(11, 0)) {
+		dev_err(i2c->dev, "requested bus frequency too low\n");
+		div_l = GENMASK(11, 0);
+	}
+
+	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV_MASK,
+			   FIELD_PREP(REG_CTRL_CLKDIV_MASK, div_h & GENMASK(9, 0)));
+
+	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT_MASK,
+			   FIELD_PREP(REG_CTRL_CLKDIVEXT_MASK, div_h >> 10));
+
+	/* set SCL low delay */
+	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_MASK,
+			   FIELD_PREP(REG_SLV_SCL_LOW_MASK, div_l));
+
+	/* Enable HIGH/LOW mode */
+	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_EN, REG_SLV_SCL_LOW_EN);
+
+	dev_dbg(i2c->dev, "%s: clk %lu, freq %u, divh %u, divl %u\n", __func__,
+		clk_rate, freq, div_h, div_l);
+}
+
+static void meson6_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
 {
 	unsigned long clk_rate = clk_get_rate(i2c->clk);
 	unsigned int div;
 
 	div = DIV_ROUND_UP(clk_rate, freq);
 	div -= FILTER_DELAY;
-	div = DIV_ROUND_UP(div, i2c->data->div_factor);
+	div = DIV_ROUND_UP(div, 4);
 
 	/* clock divider has 12 bits */
 	if (div > GENMASK(11, 0)) {
@@ -472,7 +520,9 @@ static int meson_i2c_probe(struct platform_device *pdev)
 	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR,
 			   REG_SLV_SDA_FILTER_MASK | REG_SLV_SCL_FILTER_MASK, 0);
 
-	meson_i2c_set_clk_div(i2c, timings.bus_freq_hz);
+	if (!i2c->data->set_clk_div)
+		return -EINVAL;
+	i2c->data->set_clk_div(i2c, timings.bus_freq_hz);
 
 	ret = i2c_add_adapter(&i2c->adap);
 	if (ret < 0) {
@@ -494,15 +544,15 @@ static int meson_i2c_remove(struct platform_device *pdev)
 }
 
 static const struct meson_i2c_data i2c_meson6_data = {
-	.div_factor = 4,
+	.set_clk_div = meson6_i2c_set_clk_div,
 };
 
 static const struct meson_i2c_data i2c_gxbb_data = {
-	.div_factor = 4,
+	.set_clk_div = meson_gxbb_axg_i2c_set_clk_div,
 };
 
 static const struct meson_i2c_data i2c_axg_data = {
-	.div_factor = 3,
+	.set_clk_div = meson_gxbb_axg_i2c_set_clk_div,
 };
 
 static const struct of_device_id meson_i2c_match[] = {
-- 
2.35.1

Re: [PATCH v2 2/2] i2c: meson: Use 50% duty cycle for I2C clock

[Neil Armstrong]

On 09/04/2022 18:43, Lucas Tanure wrote:
> The duty cycle of 33% is less than the required
> by the I2C specs for the LOW period of the SCL
> clock.
> 
> Move the duty cyle to 50% for 100Khz or lower
> clocks, and (40% High SCL / 60% Low SCL) duty
> cycle for clocks above 100Khz.
> 
> Signed-off-by: Lucas Tanure <tanure@linux.com>
> ---
>   drivers/i2c/busses/i2c-meson.c | 70 +++++++++++++++++++++++++++++-----
>   1 file changed, 60 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-meson.c b/drivers/i2c/busses/i2c-meson.c
> index 4b4a5b2d77ab..50dab123380a 100644
> --- a/drivers/i2c/busses/i2c-meson.c
> +++ b/drivers/i2c/busses/i2c-meson.c
> @@ -65,10 +65,6 @@ enum {
>   	STATE_WRITE,
>   };
>   
> -struct meson_i2c_data {
> -	unsigned char div_factor;
> -};
> -
>   /**
>    * struct meson_i2c - Meson I2C device private data
>    *
> @@ -109,6 +105,10 @@ struct meson_i2c {
>   	const struct meson_i2c_data *data;
>   };
>   
> +struct meson_i2c_data {
> +	void (*set_clk_div)(struct meson_i2c *i2c, unsigned int freq);
> +};
> +
>   static void meson_i2c_set_mask(struct meson_i2c *i2c, int reg, u32 mask,
>   			       u32 val)
>   {
> @@ -137,14 +137,62 @@ static void meson_i2c_add_token(struct meson_i2c *i2c, int token)
>   	i2c->num_tokens++;
>   }
>   
> -static void meson_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
> +static void meson_gxbb_axg_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
> +{
> +	unsigned long clk_rate = clk_get_rate(i2c->clk);
> +	unsigned int div_h, div_l;
> +
> +	/* According to I2C-BUS Spec 2.1, in FAST-MODE, the minimum LOW period is 1.3uS, and
> +	 * minimum HIGH is least 0.6us.
> +	 * For 400000 freq, the period is 2.5us. To keep within the specs, give 40% of period to
> +	 * HIGH and 60% to LOW. This means HIGH at 1.0us and LOW 1.5us.
> +	 * The same applies for Fast-mode plus, where LOW is 0.5us and HIGH is 0.26us.
> +	 * Duty = H/(H + L) = 2/5
> +	 */
> +	if (freq <= I2C_MAX_STANDARD_MODE_FREQ) {
> +		div_h = DIV_ROUND_UP(clk_rate, freq);
> +		div_l = DIV_ROUND_UP(div_h, 4);
> +		div_h = DIV_ROUND_UP(div_h, 2) - FILTER_DELAY;
> +	} else {
> +		div_h = DIV_ROUND_UP(clk_rate * 2, freq * 5) - FILTER_DELAY;
> +		div_l = DIV_ROUND_UP(clk_rate * 3, freq * 5 * 2);
> +	}
> +
> +	/* clock divider has 12 bits */
> +	if (div_h > GENMASK(11, 0)) {
> +		dev_err(i2c->dev, "requested bus frequency too low\n");
> +		div_h = GENMASK(11, 0);
> +	}
> +	if (div_l > GENMASK(11, 0)) {
> +		dev_err(i2c->dev, "requested bus frequency too low\n");
> +		div_l = GENMASK(11, 0);
> +	}
> +
> +	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIV_MASK,
> +			   FIELD_PREP(REG_CTRL_CLKDIV_MASK, div_h & GENMASK(9, 0)));
> +
> +	meson_i2c_set_mask(i2c, REG_CTRL, REG_CTRL_CLKDIVEXT_MASK,
> +			   FIELD_PREP(REG_CTRL_CLKDIVEXT_MASK, div_h >> 10));
> +
> +	/* set SCL low delay */
> +	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_MASK,
> +			   FIELD_PREP(REG_SLV_SCL_LOW_MASK, div_l));
> +
> +	/* Enable HIGH/LOW mode */
> +	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR, REG_SLV_SCL_LOW_EN, REG_SLV_SCL_LOW_EN);
> +
> +	dev_dbg(i2c->dev, "%s: clk %lu, freq %u, divh %u, divl %u\n", __func__,
> +		clk_rate, freq, div_h, div_l);
> +}
> +
> +static void meson6_i2c_set_clk_div(struct meson_i2c *i2c, unsigned int freq)
>   {
>   	unsigned long clk_rate = clk_get_rate(i2c->clk);
>   	unsigned int div;
>   
>   	div = DIV_ROUND_UP(clk_rate, freq);
>   	div -= FILTER_DELAY;
> -	div = DIV_ROUND_UP(div, i2c->data->div_factor);
> +	div = DIV_ROUND_UP(div, 4);
>   
>   	/* clock divider has 12 bits */
>   	if (div > GENMASK(11, 0)) {
> @@ -472,7 +520,9 @@ static int meson_i2c_probe(struct platform_device *pdev)
>   	meson_i2c_set_mask(i2c, REG_SLAVE_ADDR,
>   			   REG_SLV_SDA_FILTER_MASK | REG_SLV_SCL_FILTER_MASK, 0);
>   
> -	meson_i2c_set_clk_div(i2c, timings.bus_freq_hz);
> +	if (!i2c->data->set_clk_div)
> +		return -EINVAL;
> +	i2c->data->set_clk_div(i2c, timings.bus_freq_hz);
>   
>   	ret = i2c_add_adapter(&i2c->adap);
>   	if (ret < 0) {
> @@ -494,15 +544,15 @@ static int meson_i2c_remove(struct platform_device *pdev)
>   }
>   
>   static const struct meson_i2c_data i2c_meson6_data = {
> -	.div_factor = 4,
> +	.set_clk_div = meson6_i2c_set_clk_div,
>   };
>   
>   static const struct meson_i2c_data i2c_gxbb_data = {
> -	.div_factor = 4,
> +	.set_clk_div = meson_gxbb_axg_i2c_set_clk_div,
>   };
>   
>   static const struct meson_i2c_data i2c_axg_data = {
> -	.div_factor = 3,
> +	.set_clk_div = meson_gxbb_axg_i2c_set_clk_div,
>   };
>   
>   static const struct of_device_id meson_i2c_match[] = {

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>

Re: [PATCH v2 2/2] i2c: meson: Use 50% duty cycle for I2C clock

[Wolfram Sang]

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On Sat, Apr 09, 2022 at 05:43:34PM +0100, Lucas Tanure wrote:
> The duty cycle of 33% is less than the required
> by the I2C specs for the LOW period of the SCL
> clock.
> 
> Move the duty cyle to 50% for 100Khz or lower
> clocks, and (40% High SCL / 60% Low SCL) duty
> cycle for clocks above 100Khz.
> 
> Signed-off-by: Lucas Tanure <tanure@linux.com>

Applied to for-next, thanks!


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Re: [PATCH v2 0/2] Ensure High and Low periods of SCL are correct

[Neil Armstrong]

Hi,

On 09/04/2022 18:43, Lucas Tanure wrote:
> The default duty cycle of 33% is less than the required
> by the I2C specs for the LOW period of the SCL clock at
> 100KHz bus speed.
> 
> So, for 100Khz or less, use 50%H/50%L duty cycle, and
> for the clock above 100Khz, use 40%H/60%L duty cycle.
> That ensures the low period of SCL is always more than
> the minimum required by the specs at any given frequency.
> 
> I did a few measures on the Khadas Vim3 board:
> 
> i2c_AO (i2c@5000):
> 
> Before the patchset, I got:
> - 100KHz: 3.338us HIGH, 6.746us LOW, 33%/67%, Freq 99KHz (Not Valid tHIGH < 4.0us)
> - 400KHz: 860ns HIGH, 1.734us LOW, 33.15%/62.85%, Freq 385.505KHz (Valid)
> - 1000KHz: 362ns HIGH, 732ns LOW, 33.09%/66.91%, Freq 914.077KHz (Valid)
> 
> With the patchset
> - 100KHz: 4.952us HIGH, 5.134us LOW, 49%/51%, Freq 99KHz (Valid)
> - 400KHz: 966ns HIGH, 1.628us LOW, 37.24%/62.76%, Freq 385.505KHz (Valid)
> - 1000KHz: 372ns HIGH, 720ns LOW, 34.07%/65.93%, Freq 915.741KHz (Valid)
> 
> i2c3 (i2c@1c000):
> 
> Before the patchset, I got:
> - 100KHz: 3.348us HIGH, 6.704us LOW, 33%/67%, Freq 99.5KHz (Not Valid tHIGH < 4.0us)
> - 400KHz: 864ns HIGH, 1.69us LOW, 33.83%/62.17%, Freq 391.543KHz (Valid)
> - 1000KHz: 360ns HIGH, 690ns LOW, 34.29%/65.71%, Freq 952.381KHz (Valid)
> 
> With the patchset
> - 100KHz: 4.958us HIGH, 5.092us LOW, 49%/51%, Freq 99KHz (Valid)
> - 400KHz: 970ns HIGH, 1.582us LOW, 38%/62%, Freq 391.85KHz (Valid)
> - 1000KHz: 370ns HIGH, 680ns LOW, 35.24%/64.76%, Freq 952.57KHz (Valid)
> 
> v2 changelog:
>   - Keep the previous calculation for Meson6
>   - Use I2C_MAX_STANDARD_MODE_FREQ
>   - move the comment before the if()
>   - use FIELD_PREP for setting div_l
>   - Drop removal of meson_i2c_data
> 
> Previous versions:
>   V1: https://lkml.org/lkml/2022/3/26/109
> 
> Lucas Tanure (2):
>    i2c: meson: Use _SHIFT and _MASK for register definitions
>    i2c: meson: Use 50% duty cycle for I2C clock
> 
>   drivers/i2c/busses/i2c-meson.c | 111 ++++++++++++++++++++++++---------
>   1 file changed, 82 insertions(+), 29 deletions(-)
> 

Thanks a lot for the timings !

I think it's ok to be applied,

Neil