[PATCH v3 1/2] aspeed: i2c: add clock duty cycle property

[Potin Lai <potin.lai.pt@gmail.com>]

Introduce i2c-clk-duty-cycle property for setting a minimum clock high
percentage.

This driver calculate clk_high and clk_low with giving duty cycle. If it
could not find a suit clk_high and clk_low, it apply default duty cycle
50%.

Signed-off-by: Potin Lai <potin.lai.pt@gmail.com>
---
 drivers/i2c/busses/i2c-aspeed.c | 56 ++++++++++++++++++++++++++-------
 1 file changed, 45 insertions(+), 11 deletions(-)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index 67e8b97c0c95..825d23f79be7 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/drivers/i2c/busses/i2c-aspeed.c
@@ -19,6 +19,7 @@
 #include <linux/irqchip/chained_irq.h>
 #include <linux/irqdomain.h>
 #include <linux/kernel.h>
+#include <linux/math.h>
 #include <linux/module.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
@@ -27,6 +28,8 @@
 #include <linux/reset.h>
 #include <linux/slab.h>
 
+#define DEFAULT_I2C_CLK_DUTY_CYCLE			50
+
 /* I2C Register */
 #define ASPEED_I2C_FUN_CTRL_REG				0x00
 #define ASPEED_I2C_AC_TIMING_REG1			0x04
@@ -149,9 +152,11 @@ struct aspeed_i2c_bus {
 	spinlock_t			lock;
 	struct completion		cmd_complete;
 	u32				(*get_clk_reg_val)(struct device *dev,
-							   u32 divisor);
+							   u32 divisor,
+							   u32 duty_cycle);
 	unsigned long			parent_clk_frequency;
 	u32				bus_frequency;
+	u32				duty_cycle;
 	/* Transaction state. */
 	enum aspeed_i2c_master_state	master_state;
 	struct i2c_msg			*msgs;
@@ -798,9 +803,11 @@ static const struct i2c_algorithm aspeed_i2c_algo = {
 
 static u32 aspeed_i2c_get_clk_reg_val(struct device *dev,
 				      u32 clk_high_low_mask,
-				      u32 divisor)
+				      u32 divisor,
+				      u32 duty_cycle)
 {
 	u32 base_clk_divisor, clk_high_low_max, clk_high, clk_low, tmp;
+	u32 tmp_base_clk_divisor;
 
 	/*
 	 * SCL_high and SCL_low represent a value 1 greater than what is stored
@@ -842,10 +849,32 @@ static u32 aspeed_i2c_get_clk_reg_val(struct device *dev,
 			"clamping clock divider: divider requested, %u, is greater than largest possible divider, %u.\n",
 			divisor, (1 << base_clk_divisor) * clk_high_low_max);
 	} else {
-		tmp = (divisor + (1 << base_clk_divisor) - 1)
+		for (tmp_base_clk_divisor = base_clk_divisor;
+		    tmp_base_clk_divisor <= ASPEED_I2CD_TIME_BASE_DIVISOR_MASK;
+		    tmp_base_clk_divisor++) {
+			/* calculate clk_high and clk_low with duty cycle */
+			tmp = (divisor + (1 << tmp_base_clk_divisor) - 1)
+				>> tmp_base_clk_divisor;
+
+			clk_high = DIV_ROUND_UP(tmp * duty_cycle, 100);
+			clk_low = tmp - clk_high;
+
+			if (max(clk_high, clk_low) <= (clk_high_low_mask + 1))
+				break;
+		}
+
+		if (tmp_base_clk_divisor <= ASPEED_I2CD_TIME_BASE_DIVISOR_MASK)
+			base_clk_divisor = tmp_base_clk_divisor;
+		else {
+			dev_err(dev,
+				"could not find clk_high and clk_low with duty cycle %u%%\n, recalculate with base_clk_divisor %u and duty_cycle 50%%",
+				duty_cycle, base_clk_divisor);
+			duty_cycle = 50;
+			tmp = (divisor + (1 << base_clk_divisor) - 1)
 				>> base_clk_divisor;
-		clk_low = tmp / 2;
-		clk_high = tmp - clk_low;
+			clk_high = DIV_ROUND_UP(tmp * duty_cycle, 100);
+			clk_low = tmp - clk_high;
+		}
 
 		if (clk_high)
 			clk_high--;
@@ -863,22 +892,22 @@ static u32 aspeed_i2c_get_clk_reg_val(struct device *dev,
 			   & ASPEED_I2CD_TIME_BASE_DIVISOR_MASK);
 }
 
-static u32 aspeed_i2c_24xx_get_clk_reg_val(struct device *dev, u32 divisor)
+static u32 aspeed_i2c_24xx_get_clk_reg_val(struct device *dev, u32 divisor, u32 duty_cycle)
 {
 	/*
 	 * clk_high and clk_low are each 3 bits wide, so each can hold a max
 	 * value of 8 giving a clk_high_low_max of 16.
 	 */
-	return aspeed_i2c_get_clk_reg_val(dev, GENMASK(2, 0), divisor);
+	return aspeed_i2c_get_clk_reg_val(dev, GENMASK(2, 0), divisor, duty_cycle);
 }
 
-static u32 aspeed_i2c_25xx_get_clk_reg_val(struct device *dev, u32 divisor)
+static u32 aspeed_i2c_25xx_get_clk_reg_val(struct device *dev, u32 divisor, u32 duty_cycle)
 {
 	/*
 	 * clk_high and clk_low are each 4 bits wide, so each can hold a max
 	 * value of 16 giving a clk_high_low_max of 32.
 	 */
-	return aspeed_i2c_get_clk_reg_val(dev, GENMASK(3, 0), divisor);
+	return aspeed_i2c_get_clk_reg_val(dev, GENMASK(3, 0), divisor, duty_cycle);
 }
 
 /* precondition: bus.lock has been acquired. */
@@ -891,7 +920,7 @@ static int aspeed_i2c_init_clk(struct aspeed_i2c_bus *bus)
 	clk_reg_val &= (ASPEED_I2CD_TIME_TBUF_MASK |
 			ASPEED_I2CD_TIME_THDSTA_MASK |
 			ASPEED_I2CD_TIME_TACST_MASK);
-	clk_reg_val |= bus->get_clk_reg_val(bus->dev, divisor);
+	clk_reg_val |= bus->get_clk_reg_val(bus->dev, divisor, bus->duty_cycle);
 	writel(clk_reg_val, bus->base + ASPEED_I2C_AC_TIMING_REG1);
 	writel(ASPEED_NO_TIMEOUT_CTRL, bus->base + ASPEED_I2C_AC_TIMING_REG2);
 
@@ -1009,11 +1038,16 @@ static int aspeed_i2c_probe_bus(struct platform_device *pdev)
 		bus->bus_frequency = I2C_MAX_STANDARD_MODE_FREQ;
 	}
 
+	ret = of_property_read_u32(pdev->dev.of_node,
+				   "i2c-clk-duty-cycle-min", &bus->duty_cycle);
+	if (ret < 0 || !bus->duty_cycle || bus->duty_cycle > 100)
+		bus->duty_cycle = DEFAULT_I2C_CLK_DUTY_CYCLE;
+
 	match = of_match_node(aspeed_i2c_bus_of_table, pdev->dev.of_node);
 	if (!match)
 		bus->get_clk_reg_val = aspeed_i2c_24xx_get_clk_reg_val;
 	else
-		bus->get_clk_reg_val = (u32 (*)(struct device *, u32))
+		bus->get_clk_reg_val = (u32 (*)(struct device *, u32, u32))
 				match->data;
 
 	/* Initialize the I2C adapter */
-- 
2.17.1