Re: [PATCH v4 2/2] i2c: mux: ltc4306: LTC4306 and LTC4305 I2C multiplexer/switch

Michael Hennerich <michael.hennerich@xxxxxxxxxx> · Thu, 6 Apr 2017 13:31:20 +0200

On 06.04.2017 10:39, Peter Rosin wrote:
Hi Michael,

I would still like to hear from someone with more gpio experience.

I'll ping Linus.


Anyway, from my point of view, there's just a few minor things left,
with comments inline as usual.

Thanks for you patience!

Thanks for review.


Cheers,
peda

On 2017-04-05 15:07, michael.hennerich@xxxxxxxxxx wrote:
From: Michael Hennerich <michael.hennerich@xxxxxxxxxx>

This patch adds support for the Analog Devices / Linear Technology
LTC4306 and LTC4305 4/2 Channel I2C Bus Multiplexer/Switches.
The LTC4306 optionally provides two general purpose input/output pins
(GPIOs) that can be configured as logic inputs, opendrain outputs or
push-pull outputs via the generic GPIOLIB framework.

Signed-off-by: Michael Hennerich <michael.hennerich@xxxxxxxxxx>

---

Changes since v1:

 - Sort makefile entries
 - Sort driver includes
 - Use proper defines
 - Miscellaneous coding style fixups
 - Rename mux select callback
 - Revise i2c-mux-idle-disconnect handling
 - Add ENABLE GPIO handling on error and device removal.
 - Remove surplus of_match_device call.

Changes since v2:

 - Stop double error reporting (i2c_mux_add_adapter)
 - Change subject
 - Split dt bindings to separate patch

Changes since v3:

 - Change subject and add spaces
 - Convert to I2C_MUX_LOCKED
 - Convert to regmap
 - Remove local register cache
 - Restore previous ENABLE GPIO handling
 - Initially pulse ENABLE low
 - Eliminate i2c client struct in driver state structure
 - Simplify error return path
 - Misc minor cleanups
---
 MAINTAINERS                         |   8 +
 drivers/i2c/muxes/Kconfig           |  11 ++
 drivers/i2c/muxes/Makefile          |   1 +
 drivers/i2c/muxes/i2c-mux-ltc4306.c | 310 ++++++++++++++++++++++++++++++++++++
 4 files changed, 330 insertions(+)
 create mode 100644 drivers/i2c/muxes/i2c-mux-ltc4306.c

diff --git a/MAINTAINERS b/MAINTAINERS
index c776906..9a27a19 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7698,6 +7698,14 @@ S:	Maintained
 F:	Documentation/hwmon/ltc4261
 F:	drivers/hwmon/ltc4261.c

+LTC4306 I2C MULTIPLEXER DRIVER
+M:	Michael Hennerich <michael.hennerich@xxxxxxxxxx>
+W:	http://ez.analog.com/community/linux-device-drivers
+L:	linux-i2c@xxxxxxxxxxxxxxx
+S:	Supported
+F:	drivers/i2c/muxes/i2c-mux-ltc4306.c
+F:	Documentation/devicetree/bindings/i2c/i2c-mux-ltc4306.txt
+
 LTP (Linux Test Project)
 M:	Mike Frysinger <vapier@xxxxxxxxxx>
 M:	Cyril Hrubis <chrubis@xxxxxxx>
diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
index 10b3d17..41153b4 100644
--- a/drivers/i2c/muxes/Kconfig
+++ b/drivers/i2c/muxes/Kconfig
@@ -30,6 +30,17 @@ config I2C_MUX_GPIO
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-mux-gpio.

+config I2C_MUX_LTC4306
+	tristate "LTC LTC4306/5 I2C multiplexer"
+	select GPIOLIB
+	select REGMAP_I2C
+	help
+	  If you say yes here you get support for the LTC LTC4306 or LTC4305

This reads a bit funny, and I think you should just spell out the
first LTC? But perhaps not in the tristate above though, depending
on how long it gets?

Ok - I rename LTC -> Analog Devices


+	  I2C mux/switch devices.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called i2c-mux-ltc4306.
+
 config I2C_MUX_PCA9541
 	tristate "NXP PCA9541 I2C Master Selector"
 	help
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
index 9948fa4..ff7618c 100644
--- a/drivers/i2c/muxes/Makefile
+++ b/drivers/i2c/muxes/Makefile
@@ -6,6 +6,7 @@ obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE)	+= i2c-arb-gpio-challenge.o
 obj-$(CONFIG_I2C_DEMUX_PINCTRL)		+= i2c-demux-pinctrl.o

 obj-$(CONFIG_I2C_MUX_GPIO)	+= i2c-mux-gpio.o
+obj-$(CONFIG_I2C_MUX_LTC4306)	+= i2c-mux-ltc4306.o
 obj-$(CONFIG_I2C_MUX_MLXCPLD)	+= i2c-mux-mlxcpld.o
 obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
 obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o
diff --git a/drivers/i2c/muxes/i2c-mux-ltc4306.c b/drivers/i2c/muxes/i2c-mux-ltc4306.c
new file mode 100644
index 0000000..7d34434
--- /dev/null
+++ b/drivers/i2c/muxes/i2c-mux-ltc4306.c
@@ -0,0 +1,310 @@
+/*
+ * Linear Technology LTC4306 and LTC4305 I2C multiplexer/switch
+ *
+ * Copyright (C) 2017 Analog Devices Inc.
+ *
+ * Licensed under the GPL-2.
+ *
+ * Based on: i2c-mux-pca954x.c
+ *
+ * Datasheet: http://cds.linear.com/docs/en/datasheet/4306.pdf
+ */
+
+#include <linux/device.h>
+#include <linux/gpio.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/i2c-mux.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+#define LTC4305_MAX_NCHANS 2
+#define LTC4306_MAX_NCHANS 4
+
+#define LTC_REG_STATUS	0x0
+#define LTC_REG_CONFIG	0x1
+#define LTC_REG_MODE	0x2
+#define LTC_REG_SWITCH	0x3
+
+#define LTC_DOWNSTREAM_ACCL_EN	BIT(6)
+#define LTC_UPSTREAM_ACCL_EN	BIT(7)
+
+#define LTC_GPIO_ALL_INPUT	0xC0
+#define LTC_SWITCH_MASK		0xF0
+
+enum ltc_type {
+	ltc_4305,
+	ltc_4306,
+};
+
+struct chip_desc {
+	u8 nchans;
+	u8 num_gpios;
+};
+
+struct ltc4306 {
+	struct regmap *regmap;
+	struct gpio_chip gpiochip;
+	const struct chip_desc *chip;
+};
+
+static const struct chip_desc chips[] = {
+	[ltc_4305] = {
+		.nchans = LTC4305_MAX_NCHANS,
+	},
+	[ltc_4306] = {
+		.nchans = LTC4306_MAX_NCHANS,
+		.num_gpios = 2,
+	},
+};
+
+static bool ltc4306_is_volatile_reg(struct device *dev, unsigned int reg)
+{
+	return (reg == LTC_REG_CONFIG) ? true : false;
+}
+
+static const struct regmap_config ltc4306_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = LTC_REG_SWITCH,
+	.volatile_reg = ltc4306_is_volatile_reg,
+	.cache_type = REGCACHE_RBTREE,

Did you consider REGCACHE_FLAT? There are very few registers and no hole
in the map, and maintaining a tree seems like total overkill.

There is no reason to use REGCACHE_FLAT, in our case it will be a single 
node.


+};
+
+static int ltc4306_gpio_get(struct gpio_chip *chip, unsigned int offset)
+{
+	struct ltc4306 *data = gpiochip_get_data(chip);
+	unsigned int val;
+	int ret;
+
+	ret = regmap_read(data->regmap, LTC_REG_CONFIG, &val);
+	if (ret < 0)
+		return ret;
+
+	return (val & BIT(1 - offset));

The outer parentheses do not add anything, and I think they might remain
from when you just removed a double negation at some point. But is it
good practice to indicate "high" with anything other than one? Sure, the
gpiolib function that wraps the ->get() op does the !! dance for you,
but even so, every single one of the half dozen random gpio providers I
looked at had code to coerce the value to 0/1 (or error). Which makes me
think you should also have it. And the gpio_chip documentation on ->get()
agrees with me...

I'll restore the double negations.


+}
+
+static void ltc4306_gpio_set(struct gpio_chip *chip, unsigned int offset,
+			     int value)
+{
+	struct ltc4306 *data = gpiochip_get_data(chip);
+
+	regmap_update_bits(data->regmap, LTC_REG_CONFIG, BIT(5 - offset),
+			   value ? BIT(5 - offset) : 0);
+}
+
+static int ltc4306_gpio_direction_input(struct gpio_chip *chip,
+					unsigned int offset)
+{
+	struct ltc4306 *data = gpiochip_get_data(chip);
+
+	return regmap_update_bits(data->regmap, LTC_REG_MODE,
+				  BIT(7 - offset), BIT(7 - offset));
+}
+
+static int ltc4306_gpio_direction_output(struct gpio_chip *chip,
+					 unsigned int offset, int value)
+{
+	struct ltc4306 *data = gpiochip_get_data(chip);
+
+	ltc4306_gpio_set(chip, offset, value);
+	return regmap_update_bits(data->regmap, LTC_REG_MODE,
+				  BIT(7 - offset), 0);
+}
+
+static int ltc4306_gpio_set_config(struct gpio_chip *chip,
+				   unsigned int offset, unsigned long config)
+{
+	struct ltc4306 *data = gpiochip_get_data(chip);
+	unsigned int val;
+
+	switch (pinconf_to_config_param(config)) {
+	case PIN_CONFIG_DRIVE_OPEN_DRAIN:
+		val = 0;
+		break;
+	case PIN_CONFIG_DRIVE_PUSH_PULL:
+		val = BIT(4 - offset);
+		break;
+	default:
+		return -ENOTSUPP;
+	}
+
+	return regmap_update_bits(data->regmap, LTC_REG_MODE,
+				  BIT(4 - offset), val);
+}
+
+static int ltc4306_gpio_init(struct ltc4306 *data)
+{
+	struct device *dev = regmap_get_device(data->regmap);
+
+	if (!data->chip->num_gpios)
+		return 0;
+
+	data->gpiochip.label = dev_name(dev);
+	data->gpiochip.base = -1;
+	data->gpiochip.ngpio = data->chip->num_gpios;
+	data->gpiochip.parent = dev;
+	data->gpiochip.can_sleep = true;
+	data->gpiochip.direction_input = ltc4306_gpio_direction_input;
+	data->gpiochip.direction_output = ltc4306_gpio_direction_output;

I'm missing a get_direction op?

No - its purely optional - the vast majority of gpiochips don't 
implement it.

linux/drivers/gpio$ grep -lr --include \*.c get_direction | wc
     36      36     523
linux/drivers/gpio$ grep -Lr --include \*.c get_direction | wc
    101     101    1461

+	data->gpiochip.get = ltc4306_gpio_get;
+	data->gpiochip.set = ltc4306_gpio_set;
+	data->gpiochip.set_config = ltc4306_gpio_set_config;
+	data->gpiochip.owner = THIS_MODULE;
+
+	/* gpiolib assumes all GPIOs default input */
+	regmap_write(data->regmap, LTC_REG_MODE, LTC_GPIO_ALL_INPUT);
+
+	return devm_gpiochip_add_data(dev, &data->gpiochip, data);
+}
+
+static int ltc4306_select_mux(struct i2c_mux_core *muxc, u32 chan)
+{
+	struct ltc4306 *data = i2c_mux_priv(muxc);
+
+	return regmap_update_bits(data->regmap, LTC_REG_SWITCH,
+				  LTC_SWITCH_MASK, BIT(7 - chan));

Since the bits outside the mask are ignored for writes, I'd go with
regmap_write. Especially since those bits are volatile, which admittedly
will not have much impact until there is a need to read those volatile
bits outside the mask. But still.

Yes they are volatile - but not declared as such.
So regmap cache just ignores them.
And we totally ignore these RONLY status bits, too.
regmap_write() will always write and ignore the cache, while 
regmap_update_bits() uses the cached value.

Are these callbacks guaranteed to be never called with the same CHAN 
sequentially? if yes - use regmap_write() otherwise its more efficient 
to use regmap_update_bits().


+}
+
+static int ltc4306_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
+{
+	struct ltc4306 *data = i2c_mux_priv(muxc);
+
+	return regmap_update_bits(data->regmap, LTC_REG_SWITCH,
+				  LTC_SWITCH_MASK, 0);

Dito.

+}
+
+static const struct i2c_device_id ltc4306_id[] = {
+	{ "ltc4305", ltc_4305 },
+	{ "ltc4306", ltc_4306 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ltc4306_id);
+
+static const struct of_device_id ltc4306_of_match[] = {
+	{ .compatible = "lltc,ltc4305", .data = &chips[ltc_4305] },
+	{ .compatible = "lltc,ltc4306", .data = &chips[ltc_4306] },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ltc4306_of_match);
+
+static int ltc4306_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct i2c_adapter *adap = to_i2c_adapter(client->dev.parent);
+	struct device_node *of_node = client->dev.of_node;
+	struct i2c_mux_core *muxc;
+	struct ltc4306 *data;
+	struct gpio_desc *gpio;
+	bool idle_disc = false;
+	int num, ret;
+
+	if (of_node)
+		idle_disc = of_property_read_bool(of_node,
+						  "i2c-mux-idle-disconnect");
+
+	muxc = i2c_mux_alloc(adap, &client->dev,
+			     LTC4306_MAX_NCHANS, sizeof(*data),

Hmmm, I didn't see this before, but if you do some more rearranging, it
should be possible to replace LTC4306_MAX_NCHANS with data->chip->nchans
and reduce resource waste for ltc4305. But it's just storage for two
pointers which is really really minor... Feel free to ignore.

But you want to set a good example, right :-)

+			     I2C_MUX_LOCKED, ltc4306_select_mux,
+			     idle_disc ? ltc4306_deselect_mux : NULL);
+	if (!muxc)
+		return -ENOMEM;
+	data = i2c_mux_priv(muxc);
+
+	i2c_set_clientdata(client, muxc);
+
+	data->regmap = devm_regmap_init_i2c(client, &ltc4306_regmap_config);
+	if (IS_ERR(data->regmap)) {
+		ret = PTR_ERR(data->regmap);
+		dev_err(&client->dev, "Failed to allocate register map: %d\n",
+			ret);
+		return ret;
+	}
+
+	/* Reset and enable the mux if an enable GPIO is specified. */
+	gpio = devm_gpiod_get_optional(&client->dev, "enable", GPIOD_OUT_LOW);
+	if (IS_ERR(gpio))
+		return PTR_ERR(gpio);
+
+	if (gpio) {
+		udelay(1);
+		gpiod_set_value(gpio, 1);
+	}
+
+	/*
+	 * Write the mux register at addr to verify
+	 * that the mux is in fact present. This also
+	 * initializes the mux to disconnected state.
+	 */
+	if (regmap_write(data->regmap, LTC_REG_SWITCH, 0) < 0) {
+		dev_warn(&client->dev, "probe failed\n");
+		return -ENODEV;
+	}
+
+	if (of_node) {
+		unsigned int val = 0;
+
+		data->chip = of_device_get_match_data(&client->dev);
+
+		if (of_property_read_bool(of_node,
+					  "ltc,downstream-accelerators-enable"))
+			val |= LTC_DOWNSTREAM_ACCL_EN;
+
+		if (of_property_read_bool(of_node,
+					  "ltc,upstream-accelerators-enable"))
+			val |= LTC_UPSTREAM_ACCL_EN;
+
+		if (regmap_write(data->regmap, LTC_REG_CONFIG, val) < 0)
+			return -ENODEV;
+	} else {
+		data->chip = &chips[id->driver_data];
+	}
+
+	ret = ltc4306_gpio_init(data);
+	if (ret < 0)
+		return ret;
+
+	/* Now create an adapter for each channel */
+	for (num = 0; num < data->chip->nchans; num++) {
+		ret = i2c_mux_add_adapter(muxc, 0, num, 0);
+		if (ret) {
+			i2c_mux_del_adapters(muxc);
+			return ret;
+		}
+	}
+
+	dev_info(&client->dev,
+		 "registered %d multiplexed busses for I2C switch %s\n",
+		 num, client->name);
+
+	return 0;
+}
+
+static int ltc4306_remove(struct i2c_client *client)
+{
+	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
+
+	i2c_mux_del_adapters(muxc);
+
+	return 0;
+}
+
+static struct i2c_driver ltc4306_driver = {
+	.driver		= {
+		.name	= "ltc4306",
+		.of_match_table = of_match_ptr(ltc4306_of_match),
+	},
+	.probe		= ltc4306_probe,
+	.remove		= ltc4306_remove,
+	.id_table	= ltc4306_id,
+};
+
+module_i2c_driver(ltc4306_driver);
+
+MODULE_AUTHOR("Michael Hennerich <michael.hennerich@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Linear Technology LTC4306, LTC4305 I2C mux/switch driver");
+MODULE_LICENSE("GPL v2");





--
Greetings,
Michael

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