Message-ID: <0d4c068f-d909-64be-421d-4500da7ebd4c@axentia.se>
Date:   Fri, 31 Mar 2017 17:29:29 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     <michael.hennerich@...log.com>, <wsa@...-dreams.de>,
        <robh+dt@...nel.org>, <mark.rutland@....com>,
        <linus.walleij@...aro.org>
CC:     <linux-i2c@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-gpio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] i2c/muxes/i2c-mux-ltc4306: LTC4306 and LTC4305 I2C
 multiplexer/switch

Hi!

Sorry for my incremental reviewing...

There's a question for the gpio people below that I would like
to have some confirmation on. Thanks!

On 2017-03-29 12:15, michael.hennerich@...log.com wrote:
> From: Michael Hennerich <michael.hennerich@...log.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.
> 
> Signed-off-by: Michael Hennerich <michael.hennerich@...log.com>
> 
> ---
> 
> 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.
> ---
>  .../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                | 367 +++++++++++++++++++++
>  5 files changed, 447 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@...log.com>
> +W:	http://ez.analog.com/community/linux-device-drivers
> +L:	linux-i2c@...r.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@...too.org>
>  M:	Cyril Hrubis <chrubis@...e.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..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..c15a8a4
> --- /dev/null
> +++ b/drivers/i2c/muxes/i2c-mux-ltc4306.c
> @@ -0,0 +1,367 @@
> +/*
> + * 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/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)

Maybe align the BIT(x) parts with a tab, like you do above...

> +
> +#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_desc *en_gpio;
> +	struct gpio_chip gpiochip;
> +	const struct chip_desc *chip;
> +	u8 regs[LTC_REG_SWITCH + 1];
> +};
> +
> +/* Provide specs for the PCA954x types we know about */
> +static const struct chip_desc chips[] = {
> +	[ltc_4305] = {
> +		.nchans = LTC4305_MAX_NCHANS,
> +	},
> +	[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;

This assignment is not needed.

> +
> +	if (gpiochip_line_is_open_drain(chip, offset) ||
> +	    (data->regs[LTC_REG_MODE] & BIT(7 - offset))) {

I wonder about this open-coded register cache. So, gpio people, is there
a guarantee from gpiolib that only one gpio_chip operation is in flight
concurrently? Because I don't see any evidence of that. With that in
mind, I think some locking is needed?

> +		/* 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);
> +
> +	i2c_smbus_write_byte_data(data->client, LTC_REG_CONFIG,
> +				  data->regs[LTC_REG_CONFIG]);
> +}
> +
> +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]);
> +
> +	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;
> +}
> +
> +static int ltc4306_select_mux(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;
> +
> +	/* Deselect all channels */
> +	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 i2c_mux_core *muxc;
> +	struct ltc4306 *data;
> +	int num, ret;
> +
> +	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
> +		return -ENODEV;
> +
> +	if (of_node) {
> +		idle_disconnect_dt =
> +		of_property_read_bool(of_node,
> +				      "i2c-mux-idle-disconnect");

If you rename the variable "disconnect" or something similar and
shorter, you can avoid the interesting indentation.

> +	}
> +
> +	muxc = i2c_mux_alloc(adap, &client->dev,
> +			     LTC4306_MAX_NCHANS, sizeof(*data), 0,
> +			     ltc4306_select_mux, idle_disconnect_dt ?
> +			     ltc4306_deselect_mux : NULL);
> +	if (!muxc)
> +		return -ENOMEM;
> +	data = i2c_mux_priv(muxc);
> +
> +	i2c_set_clientdata(client, muxc);
> +	data->client = client;
> +
> +	/* Enable the mux if an enable GPIO is specified. */
> +	data->en_gpio = devm_gpiod_get_optional(&client->dev, "enable",
> +						GPIOD_OUT_HIGH);
> +	if (IS_ERR(data->en_gpio))
> +		return PTR_ERR(data->en_gpio);
> +
> +	/*
> +	 * 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_data(client, LTC_REG_SWITCH, 0) < 0) {
> +		dev_warn(&client->dev, "probe failed\n");
> +		ret = -ENODEV;
> +		goto gpio_default;
> +	}
> +
> +	if (of_node) {
> +		data->chip = of_device_get_match_data(&client->dev);
> +
> +		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");
> +			ret = -ENODEV;
> +			goto gpio_default;
> +		}
> +	} else {
> +		data->chip = &chips[id->driver_data];
> +	}
> +
> +	ret = ltc4306_gpio_init(data);
> +	if (ret < 0)
> +		goto gpio_default;
> +
> +	/* 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) {
> +			dev_err(&client->dev,
> +				"failed to register multiplexed adapter %d\n",
> +				num);
> +			goto add_adapter_failed;
> +		}
> +	}
> +
> +	dev_info(&client->dev,
> +		 "registered %d multiplexed busses for I2C switch %s\n",
> +		 num, client->name);
> +
> +	return 0;
> +
> +add_adapter_failed:
> +	i2c_mux_del_adapters(muxc);
> +gpio_default:
> +	gpiod_direction_input(data->en_gpio);

This was actually not what I had in mind when I asked about it in v1, and
this looks a bit strange. You have no way of knowing if the pin was
configured as input when probe was called, and I don't see code like this
all over the place. Maybe it's is ok to not disable the chip over
suspend/resume, I was just asking because it looked a bit strange to grab
a pin and then forget about it. Now that I think about it some more, it's
probably ok to do just that since it is perhaps not possible to make the
chip draw less power by deasserting enable, but what do I know?

However, it might be a good idea to toggle enable and deliberately reset
the chip in probe?

Cheers,
peda

> +	return ret;
> +}
> +
> +static int ltc4306_remove(struct i2c_client *client)
> +{
> +	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
> +	struct ltc4306 *data = i2c_mux_priv(muxc);
> +
> +	i2c_mux_del_adapters(muxc);
> +	gpiod_direction_input(data->en_gpio);
> +
> +	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@...log.com>");
> +MODULE_DESCRIPTION("Linear Technology LTC4306, LTC4305 I2C mux/switch driver");
> +MODULE_LICENSE("GPL v2");
> 

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