[PATCH] i2c: pca954x: Add option to skip disabling PCA954x Mux device

[PATCH] i2c: pca954x: Add option to skip disabling PCA954x Mux device

[ying.zhang22455]

From: Priyanka Jain <Priyanka.Jain@freescale.com>

On some Layerscape boards like LS2085ARDB/LS2080ARDB,
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 option to skip disabling PCA954x Mux device
if device tree contians "i2c-mux-never-disable" property
for pca954x device node.

Signed-off-by: Zhang Ying-22455 <ying.zhang22455@nxp.com>
---
 drivers/i2c/muxes/i2c-mux-pca954x.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index f1751c2..4d18fc0 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -85,6 +85,7 @@ struct pca954x {
 	struct irq_domain *irq;
 	unsigned int irq_mask;
 	raw_spinlock_t lock;
+	u8 disable_mux;		/* do not disable mux if val not 0 */
 };
 
 /* Provide specs for the PCA954x types we know about */
@@ -221,6 +222,13 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 	if (!(data->deselect & (1 << chan)))
 		return 0;
 
+#ifdef CONFIG_ARCH_LAYERSCAPE
+	if (data->disable_mux != 0)
+		data->last_chan = data->chip->nchans;
+	else
+		data->last_chan = 0;
+	return pca954x_reg_write(muxc->parent, client, data->disable_mux);
+#endif
 	/* Deselect active channel */
 	data->last_chan = 0;
 	return pca954x_reg_write(muxc->parent, client, data->last_chan);
@@ -361,6 +369,22 @@ static int pca954x_probe(struct i2c_client *client,
 		return -ENOMEM;
 	data = i2c_mux_priv(muxc);
 
+#ifdef CONFIG_ARCH_LAYERSCAPE
+	/* 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->disable_mux = of_node &&
+		of_property_read_bool(of_node, "i2c-mux-never-disable") &&
+		data->chip->muxtype == pca954x_ismux ?
+		data->chip->enable : 0;
+	/* force the first selection */
+	if (data->disable_mux != 0)
+		data->last_chan = data->chip->nchans;
+	else
+		data->last_chan = 0;
+#endif
 	i2c_set_clientdata(client, muxc);
 	data->client = client;
 
@@ -373,7 +397,11 @@ static int pca954x_probe(struct i2c_client *client,
 	 * that the mux is in fact present. This also
 	 * initializes the mux to disconnected state.
 	 */
+#ifdef CONFIG_ARCH_LAYERSCAPE
+	if (i2c_smbus_write_byte(client, data->disable_mux) < 0) {
+#else
 	if (i2c_smbus_write_byte(client, 0) < 0) {
+#endif
 		dev_warn(&client->dev, "probe failed\n");
 		return -ENODEV;
 	}
@@ -384,7 +412,9 @@ static int pca954x_probe(struct i2c_client *client,
 	else
 		data->chip = &chips[id->driver_data];
 
+#ifndef CONFIG_ARCH_LAYERSCAPE
 	data->last_chan = 0;		   /* force the first selection */
+#endif
 
 	idle_disconnect_dt = of_node &&
 		of_property_read_bool(of_node, "i2c-mux-idle-disconnect");
@@ -454,6 +484,13 @@ static int pca954x_resume(struct device *dev)
 	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 	struct pca954x *data = i2c_mux_priv(muxc);
 
+#ifdef CONFIG_ARCH_LAYERSCAPE
+	if (data->disable_mux != 0)
+		data->last_chan = data->chip->nchans;
+	else
+		data->last_chan = 0;
+	return i2c_smbus_write_byte(client, data->disable_mux);
+#endif
 	data->last_chan = 0;
 	return i2c_smbus_write_byte(client, 0);
 }
-- 
2.1.0.27.g96db324

Re: [PATCH] i2c: pca954x: Add option to skip disabling PCA954x Mux device

[Andy Shevchenko]

On Tue, May 9, 2017 at 11:20 AM,  <ying.zhang22455@nxp.com> wrote:

> On some Layerscape boards like LS2085ARDB/LS2080ARDB,
> 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 option to skip disabling PCA954x Mux device
> if device tree contians "i2c-mux-never-disable" property
> for pca954x device node.

> +#ifdef CONFIG_ARCH_LAYERSCAPE

This is 99.99% is no go.

You need to spend more time to make the driver more generic (perhaps
using device property instead) and not using ugly #ifdefery.


-- 
With Best Regards,
Andy Shevchenko