[PATCH 1/1] i2c: designware_i2c: adjust timing calculation

[Heinrich Schuchardt]

In SPL probing of the designware_i2c device on the StarFive VisionFive 2
board fails with

    dw_i2c: mode 0, ic_clk 1000000, speed 100000,
    period 10 rise 1 fall 1 tlow 5 thigh 4 spk 0
    dw_i2c: bad counts. hcnt = -4 lcnt = 4
    device_probe: i2c at 12050000 failed to probe -22

When changing the offset for the high phase from 7 to 1 the device is
probed correctly.

Without this fix the memory size of the StarFive VisionFive 2 board cannot
be read from EEPROM.

Fixes: e71b6f6622d6 ("i2c: designware_i2c: Rewrite timing calculation")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
 drivers/i2c/designware_i2c.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/designware_i2c.c b/drivers/i2c/designware_i2c.c
index e54de42abc..55e582091c 100644
--- a/drivers/i2c/designware_i2c.c
+++ b/drivers/i2c/designware_i2c.c
@@ -155,10 +155,10 @@ static int dw_i2c_calc_timing(struct dw_i2c *priv, enum i2c_speed_mode mode,
 
 	/*
 	 * Back-solve for hcnt and lcnt according to the following equations:
-	 * SCL_High_time = [(HCNT + IC_*_SPKLEN + 7) * ic_clk] + SCL_Fall_time
+	 * SCL_High_time = [(HCNT + IC_*_SPKLEN + 1) * ic_clk] + SCL_Fall_time
 	 * SCL_Low_time = [(LCNT + 1) * ic_clk] - SCL_Fall_time + SCL_Rise_time
 	 */
-	hcnt = min_thigh_cnt - fall_cnt - 7 - spk_cnt;
+	hcnt = min_thigh_cnt - fall_cnt - 1 - spk_cnt;
 	lcnt = min_tlow_cnt - rise_cnt + fall_cnt - 1;
 
 	if (hcnt < 0 || lcnt < 0) {
@@ -170,13 +170,13 @@ static int dw_i2c_calc_timing(struct dw_i2c *priv, enum i2c_speed_mode mode,
 	 * Now add things back up to ensure the period is hit. If it is off,
 	 * split the difference and bias to lcnt for remainder
 	 */
-	tot = hcnt + lcnt + 7 + spk_cnt + rise_cnt + 1;
+	tot = hcnt + lcnt + 1 + spk_cnt + rise_cnt + 1;
 
 	if (tot < period_cnt) {
 		diff = (period_cnt - tot) / 2;
 		hcnt += diff;
 		lcnt += diff;
-		tot = hcnt + lcnt + 7 + spk_cnt + rise_cnt + 1;
+		tot = hcnt + lcnt + 1 + spk_cnt + rise_cnt + 1;
 		lcnt += period_cnt - tot;
 	}
 
-- 
2.40.1