ITE: drivers/i2c: Adjust the prescale of I2C SCL low and high period

When adjusting the prescale to increase the I2C SCL low period,
the high period must also be subtracted to maintain a consistent
frequency.

Signed-off-by: Tim Lin <[email protected]>

drivers/i2c/i2c_ite_enhance.c

@@ -294,8 +294,9 @@ static void i2c_enhanced_port_set_frequency(const struct device *dev,
 					    int freq_hz)
 {
 	const struct i2c_enhance_config *config = dev->config;
-	uint32_t clk_div, psr, pll_clock;
+	uint32_t clk_div, psr, pll_clock, psr_h, psr_l;
 	uint8_t *base = config->base;
+	uint8_t prescale_scl = config->prescale_scl_low;
 
 	pll_clock = chip_get_pll_freq();
 	/*
@@ -318,11 +319,28 @@ static void i2c_enhanced_port_set_frequency(const struct device *dev,
 		}
 
 		/* Adjust SCL low period prescale */
-		psr += config->prescale_scl_low;
+		psr_l = psr + prescale_scl;
+		if (psr_l > 0xFD) {
+			psr_l = 0xFD;
+			LOG_WRN("(psr + prescale_scl) can not be greater than 0xfd.");
+		}
+
+		/*
+		 * Adjust SCL high period prescale
+		 * The property setting prescale_scl must be less than psr and
+		 * the minimum value of psr_h is 2.
+		 */
+		if (psr > (prescale_scl + 2)) {
+			psr_h = psr - prescale_scl;
+		} else {
+			psr_h = 2;
+			LOG_WRN("prescale_scl_low should be less than (psr - 2).");
+		}
 
-		/* Set I2C Speed */
-		IT8XXX2_I2C_PSR(base) = psr & 0xFF;
-		IT8XXX2_I2C_HSPR(base) = psr & 0xFF;
+		/* Set I2C Speed for SCL low period. */
+		IT8XXX2_I2C_PSR(base) = psr_l & 0xFF;
+		/* Set I2C Speed for SCL high period. */
+		IT8XXX2_I2C_HSPR(base) = psr_h & 0xFF;
 	}
 
 }