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SubjectRe: [PATCH v4 2/2] i2c: mux: ltc4306: LTC4306 and LTC4305 I2C multiplexer/switch
From
Date
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@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.
>>
>> Signed-off-by: Michael Hennerich <michael.hennerich@analog.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.
>>
>> 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@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..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@analog.com>");
>> +MODULE_DESCRIPTION("Linear Technology LTC4306, LTC4305 I2C mux/switch driver");
>> +MODULE_LICENSE("GPL v2");
>>
>
>


--
Greetings,
Michael

--
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