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i2c: mux: pca954x: allow management of device idle state via sysfs 

The behaviour, by default, to not deselect after each transfer is
unsafe when there is a device with an address that conflicts with
another device on another mux on the same parent bus, and it
may not be convenient to use devicetree to set the deselect mux,
e.g. when running on x86_64 when ACPI is used to discover most of the
device hierarchy.

Therefore, provide the ability to set the idle state behaviour using a
new sysfs file, idle_state as a complement to the method of
instantiating the device via sysfs. The possible behaviours are
disconnect, i.e. to deselect all channels from the mux, as-is (the
default), i.e. leave the last channel selected, and set a
predetermined channel.

The current behaviour of leaving the channel as-is after each
transaction is preserved.

Signed-off-by: Robert Shearman <robert.shearman@att.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
hifive-unleashed-5.2
Robert Shearman 2019-02-28 11:43:43 +00:00 committed by Peter Rosin
parent 590085f0f2
commit f1fb64b04b
2 changed files with 97 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
Documentation/ABI/testing/sysfs-bus-i2c-devices-pca954x 100644
View File

@ -0,0 +1,20 @@
What: /sys/bus/i2c/.../idle_state
Date: January 2019
KernelVersion: 5.2
Contact: Robert Shearman <robert.shearman@att.com>
Description:
Value that exists only for mux devices that can be
written to control the behaviour of the multiplexer on
idle. Possible values:
-2 - disconnect on idle, i.e. deselect the last used
channel, which is useful when there is a device
with an address that conflicts with another
device on another mux on the same parent bus.
-1 - leave the mux as-is, which is the most optimal
setting in terms of I2C operations and is the
default mode.
0..<nchans> - set the mux to a predetermined channel,
which is useful if there is one channel that is
used almost always, and you want to reduce the
latency for normal operations after rare
transactions on other channels

85
drivers/i2c/muxes/i2c-mux-pca954x.c
View File

@ -49,6 +49,7 @@
#include <linux/pm.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <dt-bindings/mux/mux.h>
#define PCA954X_MAX_NCHANS 8
@ -84,7 +85,9 @@ struct pca954x {
const struct chip_desc *chip;
u8 last_chan; /* last register value */
u8 deselect;
/* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
s8 idle_state;
struct i2c_client *client;
struct irq_domain *irq;
@ -253,15 +256,71 @@ 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;
if (!(data->deselect & (1 << chan)))
return 0;
idle_state = READ_ONCE(data->idle_state);
if (idle_state >= 0)
/* Set the mux back to a predetermined channel */
return pca954x_select_chan(muxc, idle_state);
/* Deselect active channel */
data->last_chan = 0;
return pca954x_reg_write(muxc->parent, client, data->last_chan);
if (idle_state == MUX_IDLE_DISCONNECT) {
/* Deselect active channel */
data->last_chan = 0;
return pca954x_reg_write(muxc->parent, client,
data->last_chan);
}
/* otherwise leave as-is */
return 0;
}
static ssize_t idle_state_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct i2c_client *client = to_i2c_client(dev);
struct i2c_mux_core *muxc = i2c_get_clientdata(client);
struct pca954x *data = i2c_mux_priv(muxc);
return sprintf(buf, "%d\n", READ_ONCE(data->idle_state));
}
static ssize_t idle_state_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
struct i2c_client *client = to_i2c_client(dev);
struct i2c_mux_core *muxc = i2c_get_clientdata(client);
struct pca954x *data = i2c_mux_priv(muxc);
int val;
int ret;
ret = kstrtoint(buf, 0, &val);
if (ret < 0)
return ret;
if (val != MUX_IDLE_AS_IS && val != MUX_IDLE_DISCONNECT &&
(val < 0 || val >= data->chip->nchans))
return -EINVAL;
i2c_lock_bus(muxc->parent, I2C_LOCK_SEGMENT);
WRITE_ONCE(data->idle_state, val);
/*
* Set the mux into a state consistent with the new
* idle_state.
*/
if (data->last_chan || val != MUX_IDLE_DISCONNECT)
ret = pca954x_deselect_mux(muxc, 0);
i2c_unlock_bus(muxc->parent, I2C_LOCK_SEGMENT);
return ret < 0 ? ret : count;
}
static DEVICE_ATTR_RW(idle_state);
static irqreturn_t pca954x_irq_handler(int irq, void *dev_id)
{
struct pca954x *data = dev_id;
@ -328,8 +387,11 @@ static int pca954x_irq_setup(struct i2c_mux_core *muxc)
static void pca954x_cleanup(struct i2c_mux_core *muxc)
{
struct pca954x *data = i2c_mux_priv(muxc);
struct i2c_client *client = data->client;
int c, irq;
device_remove_file(&client->dev, &dev_attr_idle_state);
if (data->irq) {
for (c = 0; c < data->chip->nchans; c++) {
irq = irq_find_mapping(data->irq, c);
@ -410,9 +472,12 @@ static int pca954x_probe(struct i2c_client *client,
}
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)
@ -420,8 +485,6 @@ static int pca954x_probe(struct i2c_client *client,
/* Now create an adapter for each channel */
for (num = 0; num < data->chip->nchans; num++) {
data->deselect |= idle_disconnect_dt << num;
ret = i2c_mux_add_adapter(muxc, 0, num, 0);
if (ret)
goto fail_cleanup;
@ -436,6 +499,12 @@ static int pca954x_probe(struct i2c_client *client,
goto fail_cleanup;
}
/*
* The attr probably isn't going to be needed in most cases,
* so don't fail completely on error.
*/
device_create_file(dev, &dev_attr_idle_state);
dev_info(dev, "registered %d multiplexed busses for I2C %s %s\n",
num, data->chip->muxtype == pca954x_ismux
? "mux" : "switch", client->name);