Message-ID: <aJn6_c79tvy_1dhU@aspen.lan>
Date: Mon, 11 Aug 2025 15:15:25 +0100
From: Daniel Thompson <daniel@...cstar.com>
To: maudspierings@...ontroll.com
Cc: Lee Jones <lee@...nel.org>, Daniel Thompson <danielt@...nel.org>,
	Jingoo Han <jingoohan1@...il.com>, Pavel Machek <pavel@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Helge Deller <deller@....de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, dri-devel@...ts.freedesktop.org,
	linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	MaudSpieringsmaudspierings@...ontroll.com
Subject: Re: [PATCH 2/4] backlight: add max25014atg backlight

On Fri, Jul 25, 2025 at 01:09:24PM +0200, Maud Spierings via B4 Relay wrote:
> From: Maud Spierings <maudspierings@...ontroll.com>
>
> The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
> with intgrated boost controller.
>
> Signed-off-by: Maud Spierings maudspierings@...ontroll.com
> ---
>  MAINTAINERS                            |   2 +
>  drivers/video/backlight/Kconfig        |   7 +
>  drivers/video/backlight/Makefile       |   1 +
>  drivers/video/backlight/max25014.c     | 449 +++++++++++++++++++++++++++++++++
>  include/linux/platform_data/max25014.h |  24 ++

Who else included this header file? Can the code here simply be included
in the C file?


> diff --git a/drivers/video/backlight/max25014.c b/drivers/video/backlight/max25014.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..371b6017953ae5955f4dfef921980dfdedd65d85
> --- /dev/null
> +++ b/drivers/video/backlight/max25014.c
> @@ -0,0 +1,449 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Backlight driver for Maxim MAX25014
> + *
> + * Copyright (C) 2025 GOcontroll B.V.
> + * Author: Maud Spierings <maudspierings@...ontroll.com>
> + */
> +
> +#include <linux/backlight.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/platform_data/max25014.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>
> +
> +#define MAX25014_ISET_DEFAULT_100 11U
> +#define MAX_BRIGHTNESS (100U)
> +#define MIN_BRIGHTNESS (0U)
> +#define TON_MAX (130720U) /* @153Hz */
> +#define TON_STEP (1307U) /* @153Hz */
> +#define TON_MIN (0U)
> +
> +#define MAX25014_DEV_ID         (0x00U)
> +#define MAX25014_REV_ID         (0x01U)
> +#define MAX25014_ISET           (0x02U)
> +#define MAX25014_IMODE          (0x03U)
> +#define MAX25014_TON1H          (0x04U)
> +#define MAX25014_TON1L          (0x05U)
> +#define MAX25014_TON2H          (0x06U)
> +#define MAX25014_TON2L          (0x07U)
> +#define MAX25014_TON3H          (0x08U)
> +#define MAX25014_TON3L          (0x09U)
> +#define MAX25014_TON4H          (0x0AU)
> +#define MAX25014_TON4L          (0x0BU)
> +#define MAX25014_TON_1_4_LSB    (0x0CU)
> +#define MAX25014_SETTING        (0x12U)
> +#define MAX25014_DISABLE        (0x13U)
> +#define MAX25014_BSTMON         (0x14U)
> +#define MAX25014_IOUT1          (0x15U)
> +#define MAX25014_IOUT2          (0x16U)
> +#define MAX25014_IOUT3          (0x17U)
> +#define MAX25014_IOUT4          (0x18U)
> +#define MAX25014_OPEN           (0x1BU)
> +#define MAX25014_SHORT_GND      (0x1CU)
> +#define MAX25014_SHORT_LED      (0x1DU)
> +#define MAX25014_MASK           (0x1EU)
> +#define MAX25014_DIAG           (0x1FU)

Forcing all these constants to be unsigned is unusual. Is it really
needed?


> +#define MAX25014_IMODE_HDIM     BIT(2)
> +#define MAX25014_ISET_ENABLE    BIT(5)
> +#define MAX25014_ISET_PSEN      BIT(4)
> +#define MAX25014_DIAG_HW_RST    BIT(2)
> +#define MAX25014_SETTING_FPWM   GENMASK(6, 4)
> +
> +struct max25014;

This is redundant. Remove.
> +
> +struct max25014 {
> +	const char *chipname;

Why keep this value around? It is only used during the probe.

> +	struct i2c_client *client;
> +	struct backlight_device *bl;
> +	struct device *dev;

It is necessary to cache this, is it just a copy of client->dev)?


> +	struct regmap *regmap;
> +	struct max25014_platform_data *pdata;
> +	struct gpio_desc *enable;
> +	struct regulator *vin; /* regulator for boost converter Vin rail */
> +};
> +
> +static const struct regmap_config max25014_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.max_register = MAX25014_DIAG,
> +};
> +
> +/**
> + * @brief get the bit mask for the DISABLE register.
> + *
> + * @param strings the led string configuration array.
> + * @return uint8_t bits to set in the register.
> + */
> +static uint8_t strings_mask(struct max25014 *maxim)
> +{
> +	uint8_t res, i;
> +
> +	for (i = 0; i < 4; i++) {
> +		if (maxim->pdata->strings[i] == 0)
> +			res |= 1 << i;
> +	}
> +	return res;

Could this converison have happened during DT parsing?
> +}
> +
> +/**
> + * @brief control the brightness with i2c registers
> + *
> + * @param regmap trivial
> + * @param brt brightness
> + * @return int
> + */
> +static int max25014_register_control(struct regmap *regmap, uint32_t brt)
> +{
> +	uint32_t reg = TON_STEP * brt;
> +	int ret;
> +	/*
> +	 * 18 bit number lowest, 2 bits in first register,
> +	 * next lowest 8 in the L register, next 8 in the H register
> +	 * Seemingly setting the strength of only one string controls all of
> +	 * them, individual settings don't affect the outcome.
> +	 */
> +
> +	ret = regmap_write(regmap, MAX25014_TON_1_4_LSB, reg & 0b00000011);
> +	if (ret != 0)
> +		return ret;
> +	ret = regmap_write(regmap, MAX25014_TON1L, (reg >> 2) & 0b11111111);
> +	if (ret != 0)
> +		return ret;
> +	return regmap_write(regmap, MAX25014_TON1H, (reg >> 10) & 0b11111111);
> +}
> +
> +static int max25014_check_errors(struct max25014 *maxim)
> +{
> +	uint8_t i;
> +	int ret;
> +	uint32_t val;
> +
> +	ret = regmap_read(maxim->regmap, MAX25014_OPEN, &val);
> +	if (ret != 0)
> +		return ret;
> +	if (val > 0) {
> +		dev_err(maxim->dev, "Open led strings detected on:\n");
> +		for (i = 0; i < 4; i++) {
> +			if (val & 1 << i)
> +				dev_err(maxim->dev, "string %d\n", i + 1);
> +		}
> +		return -EIO;
> +	}
> +
> +	ret = regmap_read(maxim->regmap, MAX25014_SHORT_GND, &val);
> +	if (ret != 0)
> +		return ret;
> +	if (val > 0) {
> +		dev_err(maxim->dev, "Short to ground detected on:\n");
> +		for (i = 0; i < 4; i++) {
> +			if (val & 1 << i)
> +				dev_err(maxim->dev, "string %d\n", i + 1);
> +		}
> +		return -EIO;
> +	}
> +
> +	ret = regmap_read(maxim->regmap, MAX25014_SHORT_GND, &val);
> +	if (ret != 0)
> +		return ret;
> +	if (val > 0) {
> +		dev_err(maxim->dev, "Shorted led detected on:\n");
> +		for (i = 0; i < 4; i++) {
> +			if (val & 1 << i)
> +				dev_err(maxim->dev, "string %d\n", i + 1);
> +		}
> +		return -EIO;
> +	}
> +
> +	ret = regmap_read(maxim->regmap, MAX25014_DIAG, &val);
> +	if (ret != 0)
> +		return ret;
> +	/*
> +	 * The HW_RST bit always starts at 1 after power up.
> +	 * It is reset on first read, does not indicate an error.
> +	 */
> +	if (val > 0 && val != MAX25014_DIAG_HW_RST) {
> +		if (val & 0b1)
> +			dev_err(maxim->dev, "Overtemperature shutdown\n");
> +		if (val & 0b10)
> +			dev_warn(maxim->dev,
> +				 "Chip is getting too hot (>125C)\n");
> +		if (val & 0b1000)
> +			dev_err(maxim->dev, "Boost converter overvoltage\n");
> +		if (val & 0b10000)
> +			dev_err(maxim->dev, "Boost converter undervoltage\n");
> +		if (val & 0b100000)
> +			dev_err(maxim->dev, "IREF out of range\n");
> +		return -EIO;
> +	}
> +	return 0;
> +}
> +
> +/*
> + * 1. disable unused strings
> + * 2. set dim mode
> + * 3. set initial brightness
> + * 4. set setting register
> + * 5. enable the backlight
> + */
> +static int max25014_configure(struct max25014 *maxim)
> +{
> +	int ret;
> +	uint32_t val;
> +
> +	ret = regmap_write(maxim->regmap, MAX25014_DISABLE,
> +			   strings_mask(maxim));
> +	if (ret != 0)
> +		return ret;
> +
> +	ret = regmap_write(maxim->regmap, MAX25014_IMODE, MAX25014_IMODE_HDIM);
> +	if (ret != 0)
> +		return ret;
> +
> +	max25014_register_control(maxim->regmap,
> +				  maxim->pdata->initial_brightness);
> +
> +	ret = regmap_read(maxim->regmap, MAX25014_SETTING, &val);
> +	if (ret != 0)
> +		return ret;
> +
> +	ret = regmap_write(
> +		maxim->regmap, MAX25014_SETTING,
> +		val & ~MAX25014_SETTING_FPWM);
> +	if (ret != 0)
> +		return ret;
> +
> +	ret = regmap_write(maxim->regmap, MAX25014_ISET,
> +			   maxim->pdata->iset | MAX25014_ISET_ENABLE | MAX25014_ISET_PSEN);
> +	return ret;
> +}
> +
> +static int max25014_update_status(struct backlight_device *bl_dev)
> +{
> +	struct max25014 *maxim = bl_get_data(bl_dev);
> +
> +	if (bl_dev->props.state & BL_CORE_SUSPENDED)
> +		bl_dev->props.brightness = 0;
> +
> +	return max25014_register_control(maxim->regmap, bl_dev->props.brightness);
> +}
> +
> +static const struct backlight_ops max25014_bl_ops = {
> +	.options = BL_CORE_SUSPENDRESUME,
> +	.update_status = max25014_update_status,
> +};
> +
> +static int max25014_backlight_register(struct max25014 *maxim)
> +{
> +	struct backlight_device *bl;
> +	struct backlight_properties props;
> +	struct max25014_platform_data *pdata = maxim->pdata;
> +
> +	memset(&props, 0, sizeof(props));
> +	props.type = BACKLIGHT_PLATFORM;
> +	props.max_brightness = MAX_BRIGHTNESS;
> +
> +	if (pdata->initial_brightness > props.max_brightness)
> +		pdata->initial_brightness = props.max_brightness;

Handle this during DT parsing.

> +
> +	props.brightness = pdata->initial_brightness;
> +
> +	bl = devm_backlight_device_register(maxim->dev, maxim->chipname, maxim->dev,
> +					    maxim, &max25014_bl_ops, &props);
> +	if (IS_ERR(bl))
> +		return PTR_ERR(bl);
> +
> +	maxim->bl = bl;
> +
> +	return 0;
> +}

Can max25014_backlight_register() be moved into the probe function?
There is no special control flow here so this function doesn't make the
probe function any simpler.

> +
> +#ifdef CONFIG_OF
> +static int max25014_parse_dt(struct max25014 *maxim)
> +{
> +	struct device *dev = maxim->dev;
> +	struct device_node *node = dev->of_node;
> +	struct max25014_platform_data *pdata;
> +
> +	int res;
> +
> +	if (!node) {
> +		dev_err(dev, "no platform data\n");
> +		return -EINVAL;
> +	}
> +
> +	pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
> +	if (!pdata)
> +		return -ENOMEM;
> +
> +	res = of_property_count_u32_elems(node, "maxim,strings");
> +	if (res == 4) {
> +		of_property_read_u32_array(node, "maxim,strings", pdata->strings, 4);
> +	} else {
> +		dev_err(dev, "strings property not correctly defined\n");
> +		return -EINVAL;
> +	}
> +
> +	pdata->initial_brightness = 50U;
> +	of_property_read_u32(node, "default-brightness", &pdata->initial_brightness);
> +	pdata->iset = MAX25014_ISET_DEFAULT_100;
> +	of_property_read_u32(node, "maxim,iset", &pdata->iset);
> +
> +	if (pdata->iset < 0 || pdata->iset > 15) {
> +		dev_err(dev,
> +			"Invalid iset, should be a value from 0-15, entered was %d\n",
> +			pdata->iset);
> +		return -EINVAL;
> +	}
> +
> +	if (pdata->initial_brightness < 0 || pdata->initial_brightness > 100) {
> +		dev_err(dev,
> +			"Invalid initial brightness, should be a value from 0-100, entered was %d\n",
> +			pdata->initial_brightness);
> +		return -EINVAL;
> +	}
> +
> +	maxim->pdata = pdata;
> +
> +	return 0;
> +}
> +#else
> +static int max25014_parse_dt(struct max25014 *maxim)
> +{
> +	dev_err(maxim->dev,
> +		"CONFIG_OF not configured, unable to parse devicetree");
> +	return -EINVAL;
> +}

What is the point of this method? New drivers shouldn't support platform
data so CONFIG_OF is required for this driver to work at all.


> +#endif
> +
> +static int max25014_probe(struct i2c_client *cl)
> ...


Daniel.

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