[PATCH v4 1/3] i3c: fix i2c and i3c scl rate by bus mode

[Vitor Soares]

Currently the I3C framework limits SCL frequency to FM speed when
dealing with a mixed slow bus, even if all I2C devices are FM+ capable.

The core was also not accounting for I3C speed limitations when
operating in mixed slow mode and was erroneously using FM+ speed as the
max I2C speed when operating in mixed fast mode.

Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
Signed-off-by: Vitor Soares <vitor.soares@xxxxxxxxxxxx>
Cc: Boris Brezillon <bbrezillon@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>
---
Changes in v4:
  Print i2c-scl and i3c-scl unconditionally when in debug mode

Changes in v3:
  Change dev_warn() to dev_dbg()

Changes in v2:
  Enhance commit message
  Add dev_warn() in case user-defined i2c rate doesn't match LVR constraint
  Add dev_warn() in case user-defined i3c rate lower than i2c rate

 drivers/i3c/master.c | 52 +++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index 5f4bd52..14980db 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -91,6 +91,12 @@ void i3c_bus_normaluse_unlock(struct i3c_bus *bus)
 	up_read(&bus->lock);
 }
 
+static struct i3c_master_controller *
+i3c_bus_to_i3c_master(struct i3c_bus *i3cbus)
+{
+	return container_of(i3cbus, struct i3c_master_controller, bus);
+}
+
 static struct i3c_master_controller *dev_to_i3cmaster(struct device *dev)
 {
 	return container_of(dev, struct i3c_master_controller, dev);
@@ -565,20 +571,39 @@ static const struct device_type i3c_masterdev_type = {
 	.groups	= i3c_masterdev_groups,
 };
 
-int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode)
+int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode,
+		     unsigned long max_i2c_scl_rate)
 {
-	i3cbus->mode = mode;
 
-	if (!i3cbus->scl_rate.i3c)
-		i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
+	struct i3c_master_controller *master = i3c_bus_to_i3c_master(i3cbus);
 
-	if (!i3cbus->scl_rate.i2c) {
-		if (i3cbus->mode == I3C_BUS_MODE_MIXED_SLOW)
-			i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
-		else
-			i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
+	i3cbus->mode = mode;
+
+	switch (i3cbus->mode) {
+	case I3C_BUS_MODE_PURE:
+		if (!i3cbus->scl_rate.i3c)
+			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
+		break;
+	case I3C_BUS_MODE_MIXED_FAST:
+		if (!i3cbus->scl_rate.i3c)
+			i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
+		if (!i3cbus->scl_rate.i2c)
+			i3cbus->scl_rate.i2c = max_i2c_scl_rate;
+		break;
+	case I3C_BUS_MODE_MIXED_SLOW:
+		if (!i3cbus->scl_rate.i2c)
+			i3cbus->scl_rate.i2c = max_i2c_scl_rate;
+		if (!i3cbus->scl_rate.i3c ||
+		    i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
+			i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
+		break;
+	default:
+		return -EINVAL;
 	}
 
+	dev_dbg(&master->dev, "i2c-scl = %ld Hz i3c-scl = %ld Hz\n",
+		i3cbus->scl_rate.i2c, i3cbus->scl_rate.i3c);
+
 	/*
 	 * I3C/I2C frequency may have been overridden, check that user-provided
 	 * values are not exceeding max possible frequency.
@@ -1966,9 +1991,6 @@ of_i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
 	/* LVR is encoded in reg[2]. */
 	boardinfo->lvr = reg[2];
 
-	if (boardinfo->lvr & I3C_LVR_I2C_FM_MODE)
-		master->bus.scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
-
 	list_add_tail(&boardinfo->node, &master->boardinfo.i2c);
 	of_node_get(node);
 
@@ -2417,6 +2439,7 @@ int i3c_master_register(struct i3c_master_controller *master,
 			const struct i3c_master_controller_ops *ops,
 			bool secondary)
 {
+	unsigned long i2c_scl_rate = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
 	struct i3c_bus *i3cbus = i3c_master_get_bus(master);
 	enum i3c_bus_mode mode = I3C_BUS_MODE_PURE;
 	struct i2c_dev_boardinfo *i2cbi;
@@ -2466,9 +2489,12 @@ int i3c_master_register(struct i3c_master_controller *master,
 			ret = -EINVAL;
 			goto err_put_dev;
 		}
+
+		if (i2cbi->lvr & I3C_LVR_I2C_FM_MODE)
+			i2c_scl_rate = I3C_BUS_I2C_FM_SCL_RATE;
 	}
 
-	ret = i3c_bus_set_mode(i3cbus, mode);
+	ret = i3c_bus_set_mode(i3cbus, mode, i2c_scl_rate);
 	if (ret)
 		goto err_put_dev;
 
-- 
2.7.4