[v5,2/3] i2c: mux: pca954x: support property idle-state

[Biwen Li]

This supports property idle-state,if present,
overrides i2c-mux-idle-disconnect.

My use cases:
	- Use the property idle-state to fix
	  an errata on LS2085ARDB and LS2088ARDB.
	- Errata id: E-00013(board LS2085ARDB and
	  LS2088ARDB revision on Rev.B, Rev.C and Rev.D).
	- About E-00013:
	  - Description: I2C1 and I2C3 buses
	    are missing pull-up.
	  - Impact: When the PCA954x device is tri-stated, the I2C bus
	    will float. This makes the I2C bus and its associated
	    downstream devices inaccessible.
	  - Hardware fix: Populate resistors R189 and R190 for I2C1
	    and resistors R228 and R229 for I2C3.
	  - Software fix: Remove the tri-state option from the PCA954x
	    driver(PCA954x always on enable status, specify a
	    channel zero in dts to fix the errata E-00013).

Signed-off-by: Biwen Li <biwen.li@xxxxxxx>
---
Change in v5:
	- add extra precaution for pca954x_init 	

Change in v4:
	- rename function
	  pca954x_calculate_chan -> pca954x_regval

Change in v3:
	- update subject and description
	- add a helper function pca954x_calculate_chan()

Change in v2:
	- update subject and description
	- add property idle-state

 drivers/i2c/muxes/i2c-mux-pca954x.c | 67 +++++++++++++++++++----------
 1 file changed, 44 insertions(+), 23 deletions(-)

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 923aa3a5a3dc..218ba1a5ed7e 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -86,7 +86,7 @@ struct pca954x {
 
 	u8 last_chan;		/* last register value */
 	/* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
-	s8 idle_state;
+	s32 idle_state;
 
 	struct i2c_client *client;
 
@@ -229,20 +229,23 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
 				I2C_SMBUS_BYTE, &dummy);
 }
 
+static u8 pca954x_regval(struct pca954x *data, u8 chan)
+{
+	/* We make switches look like muxes, not sure how to be smarter. */
+	if (data->chip->muxtype == pca954x_ismux)
+		return chan | data->chip->enable;
+	else
+		return 1 << chan;
+}
+
 static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 {
 	struct pca954x *data = i2c_mux_priv(muxc);
 	struct i2c_client *client = data->client;
-	const struct chip_desc *chip = data->chip;
 	u8 regval;
 	int ret = 0;
 
-	/* we make switches look like muxes, not sure how to be smarter */
-	if (chip->muxtype == pca954x_ismux)
-		regval = chan | chip->enable;
-	else
-		regval = 1 << chan;
-
+	regval = pca954x_regval(data, chan);
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
@@ -256,7 +259,7 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 {
 	struct pca954x *data = i2c_mux_priv(muxc);
 	struct i2c_client *client = data->client;
-	s8 idle_state;
+	s32 idle_state;
 
 	idle_state = READ_ONCE(data->idle_state);
 	if (idle_state >= 0)
@@ -402,6 +405,25 @@ static void pca954x_cleanup(struct i2c_mux_core *muxc)
 	i2c_mux_del_adapters(muxc);
 }
 
+static int pca954x_init(struct i2c_client *client, struct pca954x *data)
+{
+	int ret;
+	if (data->idle_state >= 0) {
+		data->last_chan = pca954x_regval(data, data->idle_state);
+	} else {
+		/* Disconnect multiplexer */
+		data->last_chan = 0;
+	}
+	ret = i2c_smbus_write_byte(client, data->last_chan);
+	if (ret < 0) {
+		data->last_chan = 0;
+		dev_err(&client->dev, "failed to verify the mux, \
+			the mux maybe not present in fact\n");
+	}
+
+	return ret;
+}
+
 /*
  * I2C init/probing/exit functions
  */
@@ -411,7 +433,6 @@ static int pca954x_probe(struct i2c_client *client,
 	struct i2c_adapter *adap = client->adapter;
 	struct device *dev = &client->dev;
 	struct device_node *np = dev->of_node;
-	bool idle_disconnect_dt;
 	struct gpio_desc *gpio;
 	struct i2c_mux_core *muxc;
 	struct pca954x *data;
@@ -462,23 +483,24 @@ static int pca954x_probe(struct i2c_client *client,
 		}
 	}
 
-	/* Write the mux register at addr to verify
+	data->idle_state = MUX_IDLE_AS_IS;
+	if (of_property_read_u32(np, "idle-state", &data->idle_state)) {
+		if (np && of_property_read_bool(np, "i2c-mux-idle-disconnect"))
+			data->idle_state = MUX_IDLE_DISCONNECT;
+	}
+
+	/*
+	 * Write the mux register at addr to verify
 	 * that the mux is in fact present. This also
-	 * initializes the mux to disconnected state.
+	 * initializes the mux to a channel
+	 * or disconnected state.
 	 */
-	if (i2c_smbus_write_byte(client, 0) < 0) {
+	ret = pca954x_init(client, data);
+	if (ret < 0) {
 		dev_warn(dev, "probe failed\n");
 		return -ENODEV;
 	}
 
-	data->last_chan = 0;		   /* force the first selection */
-	data->idle_state = MUX_IDLE_AS_IS;
-
-	idle_disconnect_dt = np &&
-		of_property_read_bool(np, "i2c-mux-idle-disconnect");
-	if (idle_disconnect_dt)
-		data->idle_state = MUX_IDLE_DISCONNECT;
-
 	ret = pca954x_irq_setup(muxc);
 	if (ret)
 		goto fail_cleanup;
@@ -531,8 +553,7 @@ static int pca954x_resume(struct device *dev)
 	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 	struct pca954x *data = i2c_mux_priv(muxc);
 
-	data->last_chan = 0;
-	return i2c_smbus_write_byte(client, 0);
+	return pca954x_init(client, data);
 }
 #endif
 
-- 
2.17.1