[PATCH v2 25/31] i2c: fsi: Calculate clock divider from local bus frequency

[Eddie James <eajames@linux.ibm.com>]

Use the new FSI device local bus clock to calculate the proper
i2c clock divder and look up an optional clock-frequency property
from device tree. Change the default clock divider to 7 now that
the default local bus clock divider has been reduced as well.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
---
 drivers/i2c/busses/i2c-fsi.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-fsi.c b/drivers/i2c/busses/i2c-fsi.c
index 10332693edf0..eaecf156ac31 100644
--- a/drivers/i2c/busses/i2c-fsi.c
+++ b/drivers/i2c/busses/i2c-fsi.c
@@ -27,7 +27,8 @@
 
 #define FSI_ENGID_I2C		0x7
 
-#define I2C_DEFAULT_CLK_DIV	6
+#define I2C_DEFAULT_CLK_DIV	7
+#define I2C_DEFAULT_CLK_RATE	400000
 
 /* i2c registers */
 #define I2C_FSI_FIFO		0x00
@@ -150,6 +151,7 @@ struct fsi_i2c_master {
 	u8			fifo_size;
 	struct list_head	ports;
 	struct mutex		lock;
+	u32			clock_div;
 };
 
 struct fsi_i2c_port {
@@ -194,7 +196,7 @@ static int fsi_i2c_dev_init(struct fsi_i2c_master *i2c)
 	if (rc)
 		return rc;
 
-	mode |= FIELD_PREP(I2C_MODE_CLKDIV, I2C_DEFAULT_CLK_DIV);
+	mode |= FIELD_PREP(I2C_MODE_CLKDIV, i2c->clock_div);
 	rc = fsi_i2c_write_reg(i2c->fsi, I2C_FSI_MODE, &mode);
 	if (rc)
 		return rc;
@@ -680,6 +682,7 @@ static int fsi_i2c_probe(struct device *dev)
 	struct fsi_i2c_port *port;
 	struct device_node *np;
 	u32 port_no, ports, stat;
+	u32 lbus;
 	int rc;
 
 	i2c = devm_kzalloc(dev, sizeof(*i2c), GFP_KERNEL);
@@ -689,6 +692,20 @@ static int fsi_i2c_probe(struct device *dev)
 	mutex_init(&i2c->lock);
 	i2c->fsi = to_fsi_dev(dev);
 	INIT_LIST_HEAD(&i2c->ports);
+	i2c->clock_div = I2C_DEFAULT_CLK_DIV;
+
+	lbus = fsi_device_local_bus_frequency(i2c->fsi);
+	if (lbus) {
+		u32 clock = I2C_DEFAULT_CLK_RATE;
+
+		if (!device_property_read_u32(dev, "clock-frequency", &clock)) {
+			if (!clock)
+				clock = I2C_DEFAULT_CLK_RATE;
+		}
+
+		// i2c clock rate = local bus clock / (4 * (i2c clock div + 1))
+		i2c->clock_div = (((lbus + (clock - 1)) / clock) / 4) - 1;
+	}
 
 	rc = fsi_i2c_dev_init(i2c);
 	if (rc)
-- 
2.39.3