[v2,1/2] i2c: pca954x: Add property to skip disabling PCA954x MUX device

From: Biwen Li
Date: Sun Sep 29 2019 - 23:36:22 EST


On some Layerscape boards like LS2085ARDB and LS2088ARDB,
input pull-up resistors on PCA954x MUX device are missing on board,
So, if MUX are disabled after powered-on, input lines will float
leading to incorrect functionality.

Hence, PCA954x MUX device should never be turned-off after
power-on.

Add property to skip disabling PCA954x MUX device
if device tree contains "i2c-mux-never-disable"
for PCA954x device node.

Errata ID: E-00013 on board LS2085ARDB and LS2088ARDB
(The hardware bug found on board revision
Rev.B, Rev.C and Rev.D)

Signed-off-by: Biwen Li <biwen.li@xxxxxxx>
---
Change in v2:
- update variable name
disable_mux->never_disable

drivers/i2c/muxes/i2c-mux-pca954x.c | 37 +++++++++++++++++++++++++----
1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 923aa3a5a3dc..b4647b033163 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -93,6 +93,11 @@ struct pca954x {
struct irq_domain *irq;
unsigned int irq_mask;
raw_spinlock_t lock;
+ /*
+ * never disable value will write to control register of mux
+ * to always enable mux
+ */
+ u8 never_disable;
};

/* Provide specs for the PCA954x types we know about */
@@ -258,6 +263,11 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
struct i2c_client *client = data->client;
s8 idle_state;

+ if (data->never_disable) {
+ data->last_chan = data->chip->nchans;
+ return pca954x_reg_write(muxc->parent, client, data->never_disable);
+ }
+
idle_state = READ_ONCE(data->idle_state);
if (idle_state >= 0)
/* Set the mux back to a predetermined channel */
@@ -462,16 +472,32 @@ static int pca954x_probe(struct i2c_client *client,
}
}

+ /* Errata ID E-00013 on board LS2088ARDB and LS2088ARDB:
+ * The point here is that you must not disable a mux if there
+ * are no pullups on the input or you mess up the I2C. This
+ * needs to be put into the DTS really as the kernel cannot
+ * know this otherwise.
+ */
+
+ data->never_disable = np &&
+ of_property_read_bool(np, "i2c-mux-never-disable") &&
+ data->chip->muxtype == pca954x_ismux ?
+ data->chip->enable : 0;
+
/* Write the mux register at addr to verify
* that the mux is in fact present. This also
* initializes the mux to disconnected state.
*/
- if (i2c_smbus_write_byte(client, 0) < 0) {
+ if (i2c_smbus_write_byte(client, data->never_disable) < 0) {
dev_warn(dev, "probe failed\n");
return -ENODEV;
}

- data->last_chan = 0; /* force the first selection */
+ if (data->never_disable)
+ data->last_chan = data->chip->nchans;
+ else
+ data->last_chan = 0; /* force the first selection */
+
data->idle_state = MUX_IDLE_AS_IS;

idle_disconnect_dt = np &&
@@ -531,8 +557,11 @@ 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);
+ if (data->never_disable)
+ data->last_chan = data->chip->nchans;
+ else
+ data->last_chan = 0;
+ return i2c_smbus_write_byte(client, data->never_disable);
}
#endif

--
2.17.1