backlight: apple_dwi_bl: Add Apple DWI backlight driver

Add driver for backlight controllers attached via Apple DWI 2-wire
interface, which is found on some Apple iPhones, iPads and iPod touches
with a LCD display.

Although there is an existing apple_bl driver, it is for backlight
controllers on Intel Macs attached via PCI, which is completely different
from the Samsung-derived DWI block.

Reviewed-by: "Daniel Thompson (RISCstar)" <danielt@kernel.org>
Signed-off-by: Nick Chan <towinchenmi@gmail.com>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Link: https://lore.kernel.org/r/20250214040306.16312-3-towinchenmi@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>

drivers/video/backlight/Kconfig

@@ -290,6 +290,17 @@ config BACKLIGHT_APPLE
 	  If you have an Intel-based Apple say Y to enable a driver for its
 	  backlight.
 
+config BACKLIGHT_APPLE_DWI
+	tristate "Apple DWI 2-Wire Interface Backlight Driver"
+	depends on ARCH_APPLE || COMPILE_TEST
+	help
+	  Say Y to enable the backlight driver for backlight controllers
+	  attached via the Apple DWI 2-wire interface which is found in some
+	  Apple iPhones, iPads and iPod touches.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called apple_dwi_bl.
+
 config BACKLIGHT_QCOM_WLED
 	tristate "Qualcomm PMIC WLED Driver"
 	select REGMAP

drivers/video/backlight/Makefile

@@ -23,6 +23,7 @@ obj-$(CONFIG_BACKLIGHT_ADP5520)		+= adp5520_bl.o
 obj-$(CONFIG_BACKLIGHT_ADP8860)		+= adp8860_bl.o
 obj-$(CONFIG_BACKLIGHT_ADP8870)		+= adp8870_bl.o
 obj-$(CONFIG_BACKLIGHT_APPLE)		+= apple_bl.o
+obj-$(CONFIG_BACKLIGHT_APPLE_DWI)	+= apple_dwi_bl.o
 obj-$(CONFIG_BACKLIGHT_AS3711)		+= as3711_bl.o
 obj-$(CONFIG_BACKLIGHT_BD6107)		+= bd6107.o
 obj-$(CONFIG_BACKLIGHT_CLASS_DEVICE)	+= backlight.o

drivers/video/backlight/apple_dwi_bl.c

@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+/*
+ * Driver for backlight controllers attached via Apple DWI 2-wire interface
+ *
+ * Copyright (c) 2024 Nick Chan <towinchenmi@gmail.com>
+ */
+
+#include <linux/backlight.h>
+#include <linux/bitfield.h>
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#define DWI_BL_CTL			0x0
+#define DWI_BL_CTL_SEND1		BIT(0)
+#define DWI_BL_CTL_SEND2		BIT(4)
+#define DWI_BL_CTL_SEND3		BIT(5)
+#define DWI_BL_CTL_LE_DATA		BIT(6)
+/* Only used on Apple A9 and later */
+#define DWI_BL_CTL_SEND4		BIT(12)
+
+#define DWI_BL_CMD			0x4
+#define DWI_BL_CMD_TYPE			GENMASK(31, 28)
+#define DWI_BL_CMD_TYPE_SET_BRIGHTNESS	0xa
+#define DWI_BL_CMD_DATA			GENMASK(10, 0)
+
+#define DWI_BL_CTL_SEND			(DWI_BL_CTL_SEND1 | \
+					 DWI_BL_CTL_SEND2 | \
+					 DWI_BL_CTL_SEND3 | \
+					 DWI_BL_CTL_LE_DATA | \
+					 DWI_BL_CTL_SEND4)
+
+#define DWI_BL_MAX_BRIGHTNESS		2047
+
+struct apple_dwi_bl {
+	void __iomem *base;
+};
+
+static int dwi_bl_update_status(struct backlight_device *bl)
+{
+	struct apple_dwi_bl *dwi_bl = bl_get_data(bl);
+
+	int brightness = backlight_get_brightness(bl);
+
+	u32 cmd = 0;
+
+	cmd |= FIELD_PREP(DWI_BL_CMD_DATA, brightness);
+	cmd |= FIELD_PREP(DWI_BL_CMD_TYPE, DWI_BL_CMD_TYPE_SET_BRIGHTNESS);
+
+	writel(cmd, dwi_bl->base + DWI_BL_CMD);
+	writel(DWI_BL_CTL_SEND, dwi_bl->base + DWI_BL_CTL);
+
+	return 0;
+}
+
+static int dwi_bl_get_brightness(struct backlight_device *bl)
+{
+	struct apple_dwi_bl *dwi_bl = bl_get_data(bl);
+
+	u32 cmd = readl(dwi_bl->base + DWI_BL_CMD);
+
+	return FIELD_GET(DWI_BL_CMD_DATA, cmd);
+}
+
+static const struct backlight_ops dwi_bl_ops = {
+	.options = BL_CORE_SUSPENDRESUME,
+	.get_brightness = dwi_bl_get_brightness,
+	.update_status	= dwi_bl_update_status
+};
+
+static int dwi_bl_probe(struct platform_device *dev)
+{
+	struct apple_dwi_bl *dwi_bl;
+	struct backlight_device *bl;
+	struct backlight_properties props;
+	struct resource *res;
+
+	dwi_bl = devm_kzalloc(&dev->dev, sizeof(*dwi_bl), GFP_KERNEL);
+	if (!dwi_bl)
+		return -ENOMEM;
+
+	dwi_bl->base = devm_platform_get_and_ioremap_resource(dev, 0, &res);
+	if (IS_ERR(dwi_bl->base))
+		return PTR_ERR(dwi_bl->base);
+
+	memset(&props, 0, sizeof(struct backlight_properties));
+	props.type = BACKLIGHT_PLATFORM;
+	props.max_brightness = DWI_BL_MAX_BRIGHTNESS;
+	props.scale = BACKLIGHT_SCALE_LINEAR;
+
+	bl = devm_backlight_device_register(&dev->dev, dev->name, &dev->dev,
+					dwi_bl, &dwi_bl_ops, &props);
+	if (IS_ERR(bl))
+		return PTR_ERR(bl);
+
+	platform_set_drvdata(dev, dwi_bl);
+
+	bl->props.brightness = dwi_bl_get_brightness(bl);
+
+	return 0;
+}
+
+static const struct of_device_id dwi_bl_of_match[] = {
+	{ .compatible = "apple,dwi-bl" },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, dwi_bl_of_match);
+
+static struct platform_driver dwi_bl_driver = {
+	.driver		= {
+		.name	= "apple-dwi-bl",
+		.of_match_table = dwi_bl_of_match
+	},
+	.probe		= dwi_bl_probe,
+};
+
+module_platform_driver(dwi_bl_driver);
+
+MODULE_DESCRIPTION("Apple DWI Backlight Driver");
+MODULE_AUTHOR("Nick Chan <towinchenmi@gmail.com>");
+MODULE_LICENSE("Dual MIT/GPL");