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Date:   Wed, 16 Dec 2020 14:12:13 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     cy_huang <u0084500@...il.com>
Cc:     robh+dt@...nel.org, cy_huang@...htek.com,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 1/3] mfd: rt4831: Adds support for Richtek RT4831 MFD
 core

On Sat, 12 Dec 2020, cy_huang wrote:

> From: ChiYuan Huang <cy_huang@...htek.com>
> 
> This adds support Richtek RT4831 MFD core. It includes four channel WLED driver

Drop mentions of MFD.  Just core driver will do.

> and Display Bias Voltage outputs.
> 
> Signed-off-by: ChiYuan Huang <cy_huang@...htek.com>
> ---
> since v2
> - Refine Kconfig descriptions.
> - Add copyright.
> - Refine error logs in probe.
> - Refine comment lines in remove and shutdown.
> ---
>  drivers/mfd/Kconfig       |  10 ++++
>  drivers/mfd/Makefile      |   1 +
>  drivers/mfd/rt4831-core.c | 124 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 135 insertions(+)
>  create mode 100644 drivers/mfd/rt4831-core.c
> 
> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> index 8b99a13..dfb2640 100644
> --- a/drivers/mfd/Kconfig
> +++ b/drivers/mfd/Kconfig
> @@ -1088,6 +1088,16 @@ config MFD_RDC321X
>  	  southbridge which provides access to GPIOs and Watchdog using the
>  	  southbridge PCI device configuration space.
>  
> +config MFD_RT4831
> +	tristate "Richtek RT4831 four channel WLED and Display Bias Voltage"
> +	depends on I2C
> +	select MFD_CORE
> +	select REGMAP_I2C
> +	help
> +	  This enables support for the Richtek RT4831 that includes 4 channel
> +	  WLED driving and Display Bias Voltage. It's commonly used to provide
> +	  power to the LCD display and LCD backlight.
> +
>  config MFD_RT5033
>  	tristate "Richtek RT5033 Power Management IC"
>  	depends on I2C
> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> index 1780019..4108141 100644
> --- a/drivers/mfd/Makefile
> +++ b/drivers/mfd/Makefile
> @@ -235,6 +235,7 @@ obj-$(CONFIG_MFD_MENF21BMC)	+= menf21bmc.o
>  obj-$(CONFIG_MFD_HI6421_PMIC)	+= hi6421-pmic-core.o
>  obj-$(CONFIG_MFD_HI655X_PMIC)   += hi655x-pmic.o
>  obj-$(CONFIG_MFD_DLN2)		+= dln2.o
> +obj-$(CONFIG_MFD_RT4831)	+= rt4831-core.o

Why is this called -core ...

>  obj-$(CONFIG_MFD_RT5033)	+= rt5033.o

... and this isn't?

>  obj-$(CONFIG_MFD_SKY81452)	+= sky81452.o
>  
> diff --git a/drivers/mfd/rt4831-core.c b/drivers/mfd/rt4831-core.c
> new file mode 100644
> index 00000000..f837c06
> --- /dev/null
> +++ b/drivers/mfd/rt4831-core.c
> @@ -0,0 +1,124 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (c) 2020 Richtek Technology Corp.
> + *
> + * Author: ChiYuan Huang <cy_huang@...htek.com>
> + */
> +
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/core.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +
> +#define RT4831_REG_REVISION	0x01
> +#define RT4831_REG_ENABLE	0x08
> +#define RT4831_REG_I2CPROT	0x15
> +
> +#define RICHTEK_VID		0x03
> +#define RT4831_VID_MASK		GENMASK(1, 0)
> +#define RT4831_RESET_MASK	BIT(7)
> +#define RT4831_I2CSAFETMR_MASK	BIT(0)
> +
> +static const struct mfd_cell rt4831_subdevs[] = {
> +	OF_MFD_CELL("rt4831-backlight", NULL, NULL, 0, 0, "richtek,rt4831-backlight"),
> +	MFD_CELL_NAME("rt4831-regulator")
> +};

Just a little note about these helpers.  I'm planning on unifying the
names pretty soon.  So if you have to rebase, please watch out for the
rename.

Essentially OF_MFD_CELL() will soon become MFD_CELL_OF().

> +static bool rt4831_is_accessible_reg(struct device *dev, unsigned int reg)
> +{
> +	if (reg >= RT4831_REG_REVISION && reg <= RT4831_REG_I2CPROT)
> +		return true;
> +	return false;
> +}
> +
> +static const struct regmap_config rt4831_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.max_register = RT4831_REG_I2CPROT,
> +
> +	.readable_reg = rt4831_is_accessible_reg,
> +	.writeable_reg = rt4831_is_accessible_reg,
> +};
> +
> +static int rt4831_probe(struct i2c_client *client)
> +{
> +	struct gpio_desc *enable;

My preference would be "enable_gpio" to ensure it's easily
identifiable further on.

> +	struct regmap *regmap;
> +	unsigned int val;

'val' is not a great name for a variable that is used for a specific
purpose.  How about 'revision'?

> +	int ret;
> +
> +	enable = devm_gpiod_get_optional(&client->dev, "enable", GPIOD_OUT_HIGH);
> +	if (IS_ERR(enable)) {
> +		dev_err(&client->dev, "Failed to get 'enable' GPIO\n");
> +		return PTR_ERR(enable);
> +	}
> +
> +	regmap = devm_regmap_init_i2c(client, &rt4831_regmap_config);
> +	if (IS_ERR(regmap)) {
> +		dev_err(&client->dev, "Failed to initialize regmap\n");
> +		return PTR_ERR(regmap);
> +	}
> + 
> +	ret = regmap_read(regmap, RT4831_REG_REVISION, &val);
> +	if (ret) {
> +		dev_err(&client->dev, "Failed to get H/W revision\n");
> +		return ret;
> +	}
> +
> +	if ((val & RT4831_VID_MASK) != RICHTEK_VID) {

What does VID stand for here?

The fact that I have to ask probably means it should be changed.

Variant ID perhaps?  If so, call the define 'VARIANT_ID'.

> +		dev_err(&client->dev, "VID not matched, val = 0x%02x\n", val);

Using variable names means nothing to the user.

"revision:  0x%02x" ?

> +		return -ENODEV;
> +	}
> +
> +	/*
> +	 * Used to prevent the abnormal shutdown.
> +	 * If SCL/SDA both keep low for one second to reset HW.
> +	 */
> +	ret = regmap_update_bits(regmap, RT4831_REG_I2CPROT, RT4831_I2CSAFETMR_MASK,
> +				 RT4831_I2CSAFETMR_MASK);
> +	if (ret) {
> +		dev_err(&client->dev, "Failed to enable I2C safety timer\n");
> +		return ret;
> +	}
> +
> +	return devm_mfd_add_devices(&client->dev, PLATFORM_DEVID_AUTO, rt4831_subdevs,
> +				    ARRAY_SIZE(rt4831_subdevs), NULL, 0, NULL);
> +}
> +
> +static int rt4831_remove(struct i2c_client *client)
> +{
> +	struct regmap *regmap = dev_get_regmap(&client->dev, NULL);
> +
> +	/* Disable WLED and DSV outputs */
> +	return regmap_update_bits(regmap, RT4831_REG_ENABLE, RT4831_RESET_MASK, RT4831_RESET_MASK);
> +}
> +
> +static void rt4831_shutdown(struct i2c_client *client)
> +{
> +	struct regmap *regmap = dev_get_regmap(&client->dev, NULL);
> +
> +	/* Disable WLED and DSV outputs */
> +	regmap_update_bits(regmap, RT4831_REG_ENABLE, RT4831_RESET_MASK, RT4831_RESET_MASK);
> +}
> +
> +static const struct of_device_id __maybe_unused rt4831_of_match[] = {
> +	{ .compatible = "richtek,rt4831", },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, rt4831_of_match);
> +
> +static struct i2c_driver rt4831_driver = {
> +	.driver = {
> +		.name = "rt4831",
> +		.of_match_table = of_match_ptr(rt4831_of_match),

The trend is to not use of_match_ptr() anymore, as these devices can
not be instantiated using ACPI.

> +	},
> +	.probe_new = rt4831_probe,
> +	.remove = rt4831_remove,
> +	.shutdown = rt4831_shutdown,
> +};
> +module_i2c_driver(rt4831_driver);
> +
> +MODULE_AUTHOR("ChiYuan Huang <cy_huang@...htek.com>");
> +MODULE_LICENSE("GPL v2");

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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