[PATCH v4 8/8] i2c: mediatek: modify bus speed calculation formula

[Kewei Xu <kewei.xu@mediatek.com>]

When clock-div is 0 or greater than 1, the bus speed
calculated by the old speed calculation formula will be
larger than the target speed. So we update the formula.

Signed-off-by: Kewei Xu <kewei.xu@mediatek.com>
---
 drivers/i2c/busses/i2c-mt65xx.c | 35 +++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c
index 061775489380..45939f919085 100644
--- a/drivers/i2c/busses/i2c-mt65xx.c
+++ b/drivers/i2c/busses/i2c-mt65xx.c
@@ -68,11 +68,12 @@
 #define I2C_DEFAULT_CLK_DIV		5
 #define MAX_SAMPLE_CNT_DIV		8
 #define MAX_STEP_CNT_DIV		64
-#define MAX_CLOCK_DIV			256
+#define MAX_CLOCK_DIV_8BITS		256
+#define MAX_CLOCK_DIV_5BITS		32
 #define MAX_HS_STEP_CNT_DIV		8
-#define I2C_STANDARD_MODE_BUFFER	(1000 / 2)
-#define I2C_FAST_MODE_BUFFER		(300 / 2)
-#define I2C_FAST_MODE_PLUS_BUFFER	(20 / 2)
+#define I2C_STANDARD_MODE_BUFFER	(1000 / 3)
+#define I2C_FAST_MODE_BUFFER		(300 / 3)
+#define I2C_FAST_MODE_PLUS_BUFFER	(20 / 3)
 
 #define I2C_CONTROL_RS                  (0x1 << 1)
 #define I2C_CONTROL_DMA_EN              (0x1 << 2)
@@ -719,14 +720,26 @@ static int mtk_i2c_calculate_speed(struct mtk_i2c *i2c, unsigned int clk_src,
 	unsigned int best_mul;
 	unsigned int cnt_mul;
 	int ret = -EINVAL;
+	int clock_div_constraint = 0;
 
 	if (target_speed > I2C_MAX_HIGH_SPEED_MODE_FREQ)
 		target_speed = I2C_MAX_HIGH_SPEED_MODE_FREQ;
 
+	if (i2c->default_timing_adjust) {
+		clock_div_constraint = 0;
+	} else if (i2c->dev_comp->ltiming_adjust &&
+		   i2c->ac_timing.inter_clk_div > 1) {
+		clock_div_constraint = 1;
+	} else if (i2c->dev_comp->ltiming_adjust &&
+		   i2c->ac_timing.inter_clk_div == 0) {
+		clock_div_constraint = -1;
+	}
+
 	max_step_cnt = mtk_i2c_max_step_cnt(target_speed);
 	base_step_cnt = max_step_cnt;
 	/* Find the best combination */
-	opt_div = DIV_ROUND_UP(clk_src >> 1, target_speed);
+	opt_div = DIV_ROUND_UP(clk_src >> 1, target_speed) +
+		  clock_div_constraint;
 	best_mul = MAX_SAMPLE_CNT_DIV * max_step_cnt;
 
 	/* Search for the best pair (sample_cnt, step_cnt) with
@@ -761,7 +774,8 @@ static int mtk_i2c_calculate_speed(struct mtk_i2c *i2c, unsigned int clk_src,
 	sample_cnt = base_sample_cnt;
 	step_cnt = base_step_cnt;
 
-	if ((clk_src / (2 * sample_cnt * step_cnt)) > target_speed) {
+	if ((clk_src / (2 * (sample_cnt * step_cnt - clock_div_constraint))) >
+		 target_speed) {
 		/* In this case, hardware can't support such
 		 * low i2c_bus_freq
 		 */
@@ -848,13 +862,16 @@ static int mtk_i2c_set_speed_adjust_timing(struct mtk_i2c *i2c,
 	target_speed = i2c->speed_hz;
 	parent_clk /= i2c->clk_src_div;
 
-	if (i2c->dev_comp->timing_adjust)
-		max_clk_div = MAX_CLOCK_DIV;
+	if (i2c->dev_comp->timing_adjust && i2c->dev_comp->ltiming_adjust)
+		max_clk_div = MAX_CLOCK_DIV_5BITS;
+	else if (i2c->dev_comp->timing_adjust)
+		max_clk_div = MAX_CLOCK_DIV_8BITS;
 	else
 		max_clk_div = 1;
 
 	for (clk_div = 1; clk_div <= max_clk_div; clk_div++) {
 		clk_src = parent_clk / clk_div;
+		i2c->ac_timing.inter_clk_div = clk_div - 1;
 
 		if (target_speed > I2C_MAX_FAST_MODE_PLUS_FREQ) {
 			/* Set master code speed register */
@@ -901,8 +918,6 @@ static int mtk_i2c_set_speed_adjust_timing(struct mtk_i2c *i2c,
 		break;
 	}
 
-	i2c->ac_timing.inter_clk_div = clk_div - 1;
-
 	return 0;
 }
 
-- 
2.18.0