From: Wojciech Siudy <wojciech.siudy@xxxxxxxxx>
If the channel selection or deselection times out, it indicates
a failure in the mux's I2C subsystem. Without sending a reset pulse,
a power-on-reset of the entire device would be required to restore
communication.
The datasheet specifies a minimum hold time of 4 ns for the reset
pulse, but due to the path's capacitance and the mux having its own
clock, it is recommended to extend this to approximately 1 us.
This option can be enabled using the i2c-mux-timeout-reset property
in the device tree and should only be used if the reset line is not
shared with other devices.
Signed-off-by: Wojciech Siudy <wojciech.siudy@xxxxxxxxx>
---
Changelog:
v2:
* Removed mail header from the commit log
* Decreased reset pulse hold time from 10 to 1 ms
v3:
* Make this functionality enabled by appropriate property in
devicetree
---
drivers/i2c/muxes/i2c-mux-pca954x.c | 48 ++++++++++++++++++++++-------
1 file changed, 37 insertions(+), 11 deletions(-)
diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 6f84018258c4..c9ac0f9c9408 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -110,6 +110,7 @@ struct pca954x {
u8 last_chan; /* last register value */
/* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
s32 idle_state;
+ u8 timeout_reset;
struct i2c_client *client;
@@ -316,6 +317,30 @@ static u8 pca954x_regval(struct pca954x *data, u8 chan)
return 1 << chan;
}
+static void pca954x_reset_deassert(struct pca954x *data)
+{
+ if (data->reset_cont)
+ reset_control_deassert(data->reset_cont);
+ else
+ gpiod_set_value_cansleep(data->reset_gpio, 0);
+}
+
+static void pca954x_reset_assert(struct pca954x *data)
+{
+ if (data->reset_cont)
+ reset_control_assert(data->reset_cont);
+ else
+ gpiod_set_value_cansleep(data->reset_gpio, 1);
+}
+
+static void pca954x_reset_mux(struct pca954x *data)
+{
+ dev_warn(&data->client->dev, "resetting the device\n");
+ pca954x_reset_assert(data);
+ udelay(1);
+ pca954x_reset_deassert(data);
+}
+
static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
{
struct pca954x *data = i2c_mux_priv(muxc);
@@ -329,6 +354,8 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
ret = pca954x_reg_write(muxc->parent, client, regval);
data->last_chan = ret < 0 ? 0 : regval;
}
+ if (ret == -ETIMEDOUT && (data->reset_cont || data->reset_gpio))
+ pca954x_reset_mux(data);
return ret;
}
@@ -338,6 +365,7 @@ 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;
s32 idle_state;
+ int ret = 0;
idle_state = READ_ONCE(data->idle_state);
if (idle_state >= 0)
@@ -347,13 +375,14 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
if (idle_state == MUX_IDLE_DISCONNECT) {
/* Deselect active channel */
data->last_chan = 0;
- return pca954x_reg_write(muxc->parent, client,
- data->last_chan);
+ ret = pca954x_reg_write(muxc->parent, client, data->last_chan);
+ if (ret == -ETIMEDOUT && (data->reset_cont || data->reset_gpio))
+ pca954x_reset_mux(data);
}
/* otherwise leave as-is */
- return 0;
+ return ret;
}
static ssize_t idle_state_show(struct device *dev,
@@ -543,14 +572,6 @@ static int pca954x_get_reset(struct device *dev, struct pca954x *data)
return 0;
}
-static void pca954x_reset_deassert(struct pca954x *data)
-{
- if (data->reset_cont)
- reset_control_deassert(data->reset_cont);
- else
- gpiod_set_value_cansleep(data->reset_gpio, 0);
-}
-
/*
* I2C init/probing/exit functions
*/
@@ -625,6 +646,11 @@ static int pca954x_probe(struct i2c_client *client)
data->idle_state = MUX_IDLE_DISCONNECT;
}
+ if (device_property_read_bool(dev, "i2c-mux-timeout-reset"))
+ data->timeout_reset = 1;
+ else
+ data->timeout_reset = 0;
+
/*
* Write the mux register at addr to verify
* that the mux is in fact present. This also
--
2.34.1
