Subject: Re: [PATCH] i2c/muxes/i2c-mux-ltc4306: LTC4306 and LTC4305 I2C
 multiplexer/switch
To: <michael.hennerich@analog.com>, <wsa@the-dreams.de>,
        <robh+dt@kernel.org>, <mark.rutland@arm.com>,
        <linus.walleij@linaro.org>
References: <1490278978-28357-1-git-send-email-michael.hennerich@analog.com>
CC: <linux-i2c@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-gpio@vger.kernel.org>, <linux-kernel@vger.kernel.org>
From: Peter Rosin <peda@axentia.se>
Organization: Axentia Technologies AB
Message-ID: <5e4b224d-4dba-e183-4eda-d68f57faff7e@axentia.se>
Date: Fri, 24 Mar 2017 09:01:08 +0100
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On 2017-03-23 15:22, michael.hennerich@analog.com wrote:
> From: Michael Hennerich <michael.hennerich@analog.com>
> 
> 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.

Hmmm, I'm not sure if it is ok to implement a gpio provider outside of
drivers/gpio like this? Should it be done with MFD, or is that just
adding needless complexity?

I also wonder if you have thought about implementing support for
alerts? And do you need recovery if things get stuck? I see timeout
bits and failure to connect bits in the register map...

> 
> Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> ---
>  .../devicetree/bindings/i2c/i2c-mux-ltc4306.txt    |  61 ++++
>  MAINTAINERS                                        |   8 +
>  drivers/i2c/muxes/Kconfig                          |  10 +
>  drivers/i2c/muxes/Makefile                         |   1 +
>  drivers/i2c/muxes/i2c-mux-ltc4306.c                | 365 +++++++++++++++++++++
>  5 files changed, 445 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/i2c/i2c-mux-ltc4306.txt
>  create mode 100644 drivers/i2c/muxes/i2c-mux-ltc4306.c
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-ltc4306.txt b/Documentation/devicetree/bindings/i2c/i2c-mux-ltc4306.txt
> new file mode 100644
> index 0000000..1e98c6b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i2c/i2c-mux-ltc4306.txt
> @@ -0,0 +1,61 @@
> +* Linear Technology / Analog Devices I2C bus switch
> +
> +Required Properties:
> +
> +  - compatible: Must contain one of the following.
> +    "lltc,ltc4305", "lltc,ltc4306"
> +  - reg: The I2C address of the device.
> +
> +  The following required properties are defined externally:
> +
> +  - Standard I2C mux properties. See i2c-mux.txt in this directory.
> +  - I2C child bus nodes. See i2c-mux.txt in this directory.
> +
> +Optional Properties:
> +
> +  - enable-gpios: Reference to the GPIO connected to the enable input.
> +  - i2c-mux-idle-disconnect: Boolean; if defined, forces mux to disconnect all
> +    children in idle state. This is necessary for example, if there are several
> +    multiplexers on the bus and the devices behind them use same I2C addresses.
> +  - gpio-controller: Marks the device node as a GPIO Controller.
> +  - #gpio-cells: Should be two.  The first cell is the pin number and
> +	the second cell is used to specify flags.
> +	See ../gpio/gpio.txt for more information.
> +  - ltc,downstream-accelerators-enable: Enables the rise time accelerators
> +	on the downstream port.
> +  - ltc,upstream-accelerators-enable: Enables the rise time accelerators
> +	on the upstream port.
> +
> +Example:
> +
> +	ltc4306: i2c-mux@4a {
> +		compatible = "lltc,ltc4306";
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +		reg = <0x4a>;
> +
> +		gpio-controller;
> +		#gpio-cells = <2>;
> +
> +		i2c@0 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <0>;
> +
> +			eeprom@50 {
> +				compatible = "at,24c02";
> +				reg = <0x50>;
> +			};
> +		};
> +
> +		i2c@1 {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			reg = <1>;
> +
> +			eeprom@50 {
> +				compatible = "at,24c02";
> +				reg = <0x50>;
> +			};
> +		};
> +	};
> 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@analog.com>
> +W:	http://ez.analog.com/community/linux-device-drivers
> +L:	linux-i2c@vger.kernel.org
> +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@gentoo.org>
>  M:	Cyril Hrubis <chrubis@suse.cz>
> diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
> index 10b3d17..f501b3b 100644
> --- a/drivers/i2c/muxes/Kconfig
> +++ b/drivers/i2c/muxes/Kconfig
> @@ -30,6 +30,16 @@ 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
> +	help
> +	  If you say yes here you get support for the LTC LTC4306 or LTC4305
> +	  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..a452d09 100644
> --- a/drivers/i2c/muxes/Makefile
> +++ b/drivers/i2c/muxes/Makefile
> @@ -7,6 +7,7 @@ obj-$(CONFIG_I2C_DEMUX_PINCTRL)		+= i2c-demux-pinctrl.o
>  
>  obj-$(CONFIG_I2C_MUX_GPIO)	+= i2c-mux-gpio.o
>  obj-$(CONFIG_I2C_MUX_MLXCPLD)	+= i2c-mux-mlxcpld.o
> +obj-$(CONFIG_I2C_MUX_LTC4306)	+= i2c-mux-ltc4306.o

Keep the list sorted, please.

>  obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
>  obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o
>  obj-$(CONFIG_I2C_MUX_PINCTRL)	+= i2c-mux-pinctrl.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..f0fd4d1
> --- /dev/null
> +++ b/drivers/i2c/muxes/i2c-mux-ltc4306.c
> @@ -0,0 +1,365 @@
> +/*
> + * 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/i2c.h>
> +#include <linux/i2c-mux.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/slab.h>
> +#include <linux/gpio.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/gpio/consumer.h>

Sort the includes, please.

> +
> +#define LTC4306_MAX_NCHANS 4

Why not a define for LTC4305_MAX_NCHANS as well?

> +
> +#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
> +
> +enum ltc_type {
> +	ltc_4305,
> +	ltc_4306,
> +};
> +
> +struct chip_desc {
> +	u8 nchans;
> +	u8 num_gpios;
> +};
> +
> +struct ltc4306 {
> +	struct i2c_client *client;
> +	struct gpio_chip gpiochip;
> +	const struct chip_desc *chip;
> +
> +	u8 deselect;
> +	u8 regs[LTC_REG_SWITCH + 1];

Feels like a generic register cache, can you use regmap?

> +};
> +
> +/* Provide specs for the PCA954x types we know about */
> +static const struct chip_desc chips[] = {
> +	[ltc_4305] = {
> +		.nchans = 2,
> +	},
> +	[ltc_4306] = {
> +		.nchans = LTC4306_MAX_NCHANS,
> +		.num_gpios = 2,
> +	},
> +};
> +
> +static int ltc4306_gpio_get(struct gpio_chip *chip, unsigned int offset)
> +{
> +	struct ltc4306 *data = gpiochip_get_data(chip);
> +	int ret = 0;
> +
> +	if (gpiochip_line_is_open_drain(chip, offset) ||
> +		(data->regs[LTC_REG_MODE] & BIT(7 - offset))) {

Alignment should match open parenthesis.

> +		/* Open Drain or Input */
> +		ret = i2c_smbus_read_byte_data(data->client, LTC_REG_CONFIG);
> +		if (ret < 0)
> +			return ret;
> +
> +		return !!(ret & BIT(1 - offset));
> +	} else {
> +		return !!(data->regs[LTC_REG_CONFIG] & BIT(5 - offset));
> +	}
> +}
> +
> +static void ltc4306_gpio_set(struct gpio_chip *chip, unsigned int offset,
> +			     int value)
> +{
> +	struct ltc4306 *data = gpiochip_get_data(chip);
> +
> +	if (value)
> +		data->regs[LTC_REG_CONFIG] |= BIT(5 - offset);
> +	else
> +		data->regs[LTC_REG_CONFIG] &= ~BIT(5 - offset);
> +
> +

Please don't use multiple blank lines.

> +	i2c_smbus_write_byte_data(data->client, LTC_REG_CONFIG,
> +				 data->regs[LTC_REG_CONFIG]);

Alignment should match open parenthesis.

> +}
> +
> +static int ltc4306_gpio_direction_input(struct gpio_chip *chip,
> +					unsigned int offset)
> +{
> +	struct ltc4306 *data = gpiochip_get_data(chip);
> +
> +	data->regs[LTC_REG_MODE] |= BIT(7 - offset);
> +
> +	return i2c_smbus_write_byte_data(data->client, LTC_REG_MODE,
> +					 data->regs[LTC_REG_MODE]);
> +}
> +
> +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);
> +	data->regs[LTC_REG_MODE] &= ~BIT(7 - offset);
> +
> +	return i2c_smbus_write_byte_data(data->client, LTC_REG_MODE,
> +					 data->regs[LTC_REG_MODE]);
> +}
> +
> +static int ltc4306_gpio_set_config(struct gpio_chip *chip,
> +				   unsigned int offset, unsigned long config)
> +{
> +	struct ltc4306 *data = gpiochip_get_data(chip);
> +
> +	switch (pinconf_to_config_param(config)) {
> +	case PIN_CONFIG_DRIVE_OPEN_DRAIN:
> +		data->regs[LTC_REG_MODE] &= ~BIT(4 - offset);
> +		break;
> +	case PIN_CONFIG_DRIVE_PUSH_PULL:
> +		data->regs[LTC_REG_MODE] |= BIT(4 - offset);
> +		break;
> +	default:
> +		return -ENOTSUPP;
> +	}
> +
> +	return i2c_smbus_write_byte_data(data->client, LTC_REG_MODE,
> +					 data->regs[LTC_REG_MODE]);
> +}
> +
> +static int ltc4306_gpio_init(struct ltc4306 *data)
> +{
> +	if (!data->chip->num_gpios)
> +		return 0;
> +
> +	data->gpiochip.label = dev_name(&data->client->dev);
> +	data->gpiochip.base = -1;
> +	data->gpiochip.ngpio = data->chip->num_gpios;
> +	data->gpiochip.parent = &data->client->dev;
> +	data->gpiochip.can_sleep = true;
> +	data->gpiochip.direction_input = ltc4306_gpio_direction_input;
> +	data->gpiochip.direction_output = ltc4306_gpio_direction_output;
> +	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 */
> +	data->regs[LTC_REG_MODE] |= LTC_GPIO_ALL_INPUT;
> +	i2c_smbus_write_byte_data(data->client, LTC_REG_MODE,
> +					 data->regs[LTC_REG_MODE]);

Alignment should match open parenthesis.

> +
> +	return devm_gpiochip_add_data(&data->client->dev,
> +				      &data->gpiochip, data);
> +}
> +
> +/*
> + * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
> + * as they will try to lock the adapter a second time.
> + */
> +static int ltc4306_reg_write(struct i2c_adapter *adap,
> +			     struct i2c_client *client, u8 reg, u8 val)
> +{
> +	int ret;
> +
> +	if (adap->algo->master_xfer) {
> +		struct i2c_msg msg;
> +		char buf[2];
> +
> +		msg.addr = client->addr;
> +		msg.flags = 0;
> +		msg.len = 2;
> +		buf[0] = reg;
> +		buf[1] = val;
> +		msg.buf = buf;
> +		ret = __i2c_transfer(adap, &msg, 1);
> +	} else {
> +		union i2c_smbus_data data;
> +
> +		data.byte = val;
> +		ret = adap->algo->smbus_xfer(adap, client->addr,
> +					     client->flags,
> +					     I2C_SMBUS_WRITE,
> +					     reg,
> +					     I2C_SMBUS_BYTE_DATA, &data);
> +	}
> +
> +	return ret;
> +}

You have selected to go parent-locked, but you can get rid of the above
workaround if you go mux-locked. See Documentation/i2c/i2c-topology for
how these differ. Overall, since you do have the GPIO possibility, I think
you are closing some possibilities by going parent-locked. Those GPIOs
will more easily get locked out if you build a complex tree involving
these muxes, when the mux is parent-locked.

But on the other hand, mux-locked doesn't work everywhere either, the person
who needs mux-locked can add that option if you don't want to...

> +static int ltc4306_select_chan(struct i2c_mux_core *muxc, u32 chan)
> +{
> +	struct ltc4306 *data = i2c_mux_priv(muxc);
> +	struct i2c_client *client = data->client;
> +	u8 regval;
> +	int ret = 0;
> +
> +	regval = BIT(7 - chan);
> +
> +	/* Only select the channel if its different from the last channel */
> +	if (data->regs[LTC_REG_SWITCH] != regval) {
> +		ret = ltc4306_reg_write(muxc->parent, client,
> +					LTC_REG_SWITCH, regval);
> +		data->regs[LTC_REG_SWITCH] = ret < 0 ? 0 : regval;
> +	}
> +
> +	return ret;
> +}
> +
> +static int ltc4306_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
> +{
> +	struct ltc4306 *data = i2c_mux_priv(muxc);
> +	struct i2c_client *client = data->client;
> +
> +	if (!(data->deselect & BIT(chan)))
> +		return 0;
> +
> +	/* Deselect active channel */
> +	data->regs[LTC_REG_SWITCH] = 0;
> +
> +	return ltc4306_reg_write(muxc->parent, client,
> +				 LTC_REG_SWITCH, data->regs[LTC_REG_SWITCH]);
> +}
> +
> +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;
> +	bool idle_disconnect_dt = false;
> +	struct gpio_desc *gpio;
> +	struct i2c_mux_core *muxc;
> +	struct ltc4306 *data;
> +	const struct of_device_id *match;
> +	int num, ret;
> +
> +	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
> +		return -ENODEV;
> +
> +	muxc = i2c_mux_alloc(adap, &client->dev,
> +			     LTC4306_MAX_NCHANS, sizeof(*data), 0,
> +			     ltc4306_select_chan, ltc4306_deselect_mux);

Where's the symmetry in ..._chan for select and ..._mux for deselect?

> +	if (!muxc)
> +		return -ENOMEM;
> +	data = i2c_mux_priv(muxc);
> +
> +	i2c_set_clientdata(client, muxc);
> +	data->client = client;
> +
> +	/* Enable the mux if a enable GPIO is specified. */

s/ a / an /

> +	gpio = devm_gpiod_get_optional(&client->dev, "enable", GPIOD_OUT_HIGH);
> +	if (IS_ERR(gpio))
> +		return PTR_ERR(gpio);

Should you not use this pin later as well? In suspend/resume if you add
handling for that?

> +
> +	/* Write the mux register at addr to verify
> +	 * that the mux is in fact present. This also
> +	 * initializes the mux to disconnected state.
> +	 */

Multi-line comments should start with a /* on its own line.

> +	if (i2c_smbus_write_byte_data(client, LTC_REG_SWITCH, 0) < 0) {
> +		dev_warn(&client->dev, "probe failed\n");
> +		return -ENODEV;
> +	}
> +
> +	match = of_match_device(of_match_ptr(ltc4306_of_match), &client->dev);

Just call of_device_get_match_data() directly.

> +	if (match)
> +		data->chip = of_device_get_match_data(&client->dev);
> +	else
> +		data->chip = &chips[id->driver_data];
> +
> +	if (of_node) {
> +		idle_disconnect_dt =
> +			of_property_read_bool(of_node,
> +					      "i2c-mux-idle-disconnect");
> +		if (of_property_read_bool(of_node,
> +					  "ltc,downstream-accelerators-enable"))
> +			data->regs[LTC_REG_CONFIG] |= LTC_DOWNSTREAM_ACCL_EN;
> +
> +		if (of_property_read_bool(of_node,
> +					  "ltc,upstream-accelerators-enable"))
> +			data->regs[LTC_REG_CONFIG] |= LTC_UPSTREAM_ACCL_EN;
> +
> +		if (i2c_smbus_write_byte_data(client, LTC_REG_CONFIG,
> +					      data->regs[LTC_REG_CONFIG]) < 0) {
> +			dev_warn(&client->dev, "probe failed\n");
> +			return -ENODEV;
> +		}
> +	}
> +
> +	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++) {
> +

Blank lines aren't necessary after an open brace.

> +		data->deselect |= idle_disconnect_dt << num;

Either *all* relevant bits are 1 or *all* relevant bits are 0. You
can get rid of this variable and invoke i2c_mux_alloc with NULL
instead of ltc4306_deselect_mux when not configured to disconnect
the mux. You have to delay the mux allocation to later in probe,
but I don't think it will be too hairy to accomplish that?

Cheers,
peda

> +
> +		ret = i2c_mux_add_adapter(muxc, 0, num, 0);
> +		if (ret) {
> +			dev_err(&client->dev,
> +				"failed to register multiplexed adapter %d\n",
> +				num);
> +			goto virt_reg_failed;
> +		}
> +	}
> +
> +	dev_info(&client->dev,
> +		 "registered %d multiplexed busses for I2C switch %s\n",
> +		 num, client->name);
> +
> +	return 0;
> +
> +virt_reg_failed:
> +	i2c_mux_del_adapters(muxc);
> +	return ret;
> +}
> +
> +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@analog.com>");
> +MODULE_DESCRIPTION("Linear Technology LTC4306, LTC4305 I2C mux/switch driver");
> +MODULE_LICENSE("GPL v2");
>