i2c: designware: Support non-standard bus speeds

Add support for non-standard bus speeds by treating them as detuned
versions of the slowest standard speed not less than the requested
speed.

Signed-off-by: Phil Elwell <[email protected]>

Author: pelwell

drivers/i2c/busses/i2c-designware-common.c

@@ -318,6 +318,9 @@ void i2c_dw_adjust_bus_speed(struct dw_i2c_dev *dev)
 {
 	u32 acpi_speed = i2c_dw_acpi_round_bus_speed(dev->dev);
 	struct i2c_timings *t = &dev->timings;
+	u32 wanted_speed;
+	u32 legal_speed = 0;
+	int i;
 
 	/*
 	 * Find bus speed from the "clock-frequency" device property, ACPI
@@ -329,6 +332,30 @@ void i2c_dw_adjust_bus_speed(struct dw_i2c_dev *dev)
 		t->bus_freq_hz = max(t->bus_freq_hz, acpi_speed);
 	else
 		t->bus_freq_hz = I2C_MAX_FAST_MODE_FREQ;
+
+	wanted_speed = t->bus_freq_hz;
+
+	/* For unsupported speeds, scale down the lowest speed which is faster. */
+	for (i = 0; i < ARRAY_SIZE(supported_speeds); i++) {
+		/* supported speeds is in decreasing order */
+		if (wanted_speed == supported_speeds[i]) {
+			legal_speed = 0;
+			break;
+		}
+		if (wanted_speed > supported_speeds[i])
+			break;
+
+		legal_speed = supported_speeds[i];
+	}
+
+	if (legal_speed) {
+		/*
+		 * Pretend this was the requested speed, but preserve the preferred
+		 * speed so the clock counts can be scaled.
+		 */
+		t->bus_freq_hz = legal_speed;
+		dev->wanted_bus_speed = wanted_speed;
+	}
 }
 EXPORT_SYMBOL_GPL(i2c_dw_adjust_bus_speed);
 

drivers/i2c/busses/i2c-designware-core.h

@@ -291,6 +291,7 @@ struct dw_i2c_dev {
 	u16			fp_lcnt;
 	u16			hs_hcnt;
 	u16			hs_lcnt;
+	u32			wanted_bus_speed;
 	int			(*acquire_lock)(void);
 	void			(*release_lock)(void);
 	int			semaphore_idx;

drivers/i2c/busses/i2c-designware-master.c

@@ -41,7 +41,7 @@ static void i2c_dw_configure_fifo_master(struct dw_i2c_dev *dev)
 static u16 clock_calc(struct dw_i2c_dev *dev, bool want_high)
 {
 	struct i2c_timings *t = &dev->timings;
-	u32 wanted_speed = t->bus_freq_hz;
+	u32 wanted_speed = dev->wanted_bus_speed ?: t->bus_freq_hz;
 	u32 clk_khz = i2c_dw_clk_rate(dev);
 	u32 extra_ns = want_high ? t->scl_fall_ns : t->scl_rise_ns;
 	u32 extra_cycles = (u32)((u64)clk_khz * extra_ns / 1000000);