rpi_display: add backlight driver and overlay

Add a mailbox-driven backlight controller for the Raspberry Pi DSI
touchscreen display. Requires updated GPU firmware to recognise the
mailbox request.

Signed-off-by: Gordon Hollingworth <[email protected]>

Author: P33M

drivers/video/backlight/Kconfig

@@ -265,6 +265,12 @@ config BACKLIGHT_PWM
 	  If you have a LCD backlight adjustable by PWM, say Y to enable
 	  this driver.
 
+config BACKLIGHT_RPI
+	tristate "Raspberry Pi display firmware driven backlight"
+	help
+	  If you have the Raspberry Pi DSI touchscreen display, say Y to
+	  enable the mailbox-controlled backlight driver.
+
 config BACKLIGHT_DA903X
 	tristate "Backlight Driver for DA9030/DA9034 using WLED"
 	depends on PMIC_DA903X

drivers/video/backlight/Makefile

@@ -50,6 +50,7 @@ obj-$(CONFIG_BACKLIGHT_PANDORA)		+= pandora_bl.o
 obj-$(CONFIG_BACKLIGHT_PCF50633)	+= pcf50633-backlight.o
 obj-$(CONFIG_BACKLIGHT_PM8941_WLED)	+= pm8941-wled.o
 obj-$(CONFIG_BACKLIGHT_PWM)		+= pwm_bl.o
+obj-$(CONFIG_BACKLIGHT_RPI)			+= rpi_backlight.o
 obj-$(CONFIG_BACKLIGHT_SAHARA)		+= kb3886_bl.o
 obj-$(CONFIG_BACKLIGHT_SKY81452)	+= sky81452-backlight.o
 obj-$(CONFIG_BACKLIGHT_TOSA)		+= tosa_bl.o

drivers/video/backlight/rpi_backlight.c

@@ -0,0 +1,119 @@
+/*
+ * rpi_bl.c - Backlight controller through VPU
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/backlight.h>
+#include <linux/err.h>
+#include <linux/fb.h>
+#include <linux/gpio.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_gpio.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <soc/bcm2835/raspberrypi-firmware.h>
+
+struct rpi_backlight {
+	struct device *dev;
+	struct device *fbdev;
+	struct rpi_firmware *fw;
+};
+
+static int rpi_backlight_update_status(struct backlight_device *bl)
+{
+	struct rpi_backlight *gbl = bl_get_data(bl);
+	int brightness = bl->props.brightness;
+	int ret;
+
+	if (bl->props.power != FB_BLANK_UNBLANK ||
+	    bl->props.fb_blank != FB_BLANK_UNBLANK ||
+	    bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
+		brightness = 0;
+
+	ret = rpi_firmware_property(gbl->fw,
+			RPI_FIRMWARE_FRAMEBUFFER_SET_BACKLIGHT,
+			&brightness, sizeof(brightness));
+	if (ret) {
+		dev_err(gbl->dev, "Failed to set brightness\n");
+		return ret;
+	}
+
+	if (brightness < 0) {
+		dev_err(gbl->dev, "Backlight change failed\n");
+		return -EAGAIN;
+	}
+
+	return 0;
+}
+
+static const struct backlight_ops rpi_backlight_ops = {
+	.options	= BL_CORE_SUSPENDRESUME,
+	.update_status	= rpi_backlight_update_status,
+};
+
+static int rpi_backlight_probe(struct platform_device *pdev)
+{
+	struct backlight_properties props;
+	struct backlight_device *bl;
+	struct rpi_backlight *gbl;
+	struct device_node *fw_node;
+
+	gbl = devm_kzalloc(&pdev->dev, sizeof(*gbl), GFP_KERNEL);
+	if (gbl == NULL)
+		return -ENOMEM;
+
+	gbl->dev = &pdev->dev;
+
+	fw_node = of_parse_phandle(pdev->dev.of_node, "firmware", 0);
+	if (!fw_node) {
+		dev_err(&pdev->dev, "Missing firmware node\n");
+		return -ENOENT;
+	}
+
+	gbl->fw = rpi_firmware_get(fw_node);
+	if (!gbl->fw)
+		return -EPROBE_DEFER;
+
+	memset(&props, 0, sizeof(props));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = 255;
+	bl = devm_backlight_device_register(&pdev->dev, dev_name(&pdev->dev),
+					&pdev->dev, gbl, &rpi_backlight_ops,
+					&props);
+	if (IS_ERR(bl)) {
+		dev_err(&pdev->dev, "failed to register backlight\n");
+		return PTR_ERR(bl);
+	}
+
+	bl->props.brightness = 255;
+	backlight_update_status(bl);
+
+	platform_set_drvdata(pdev, bl);
+	return 0;
+}
+
+static const struct of_device_id rpi_backlight_of_match[] = {
+	{ .compatible = "raspberrypi,rpi-backlight" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, rpi_backlight_of_match);
+
+static struct platform_driver rpi_backlight_driver = {
+	.driver		= {
+		.name		= "rpi-backlight",
+		.of_match_table = of_match_ptr(rpi_backlight_of_match),
+	},
+	.probe		= rpi_backlight_probe,
+};
+
+module_platform_driver(rpi_backlight_driver);
+
+MODULE_AUTHOR("Gordon Hollingworth <[email protected]>");
+MODULE_DESCRIPTION("Raspberry Pi mailbox based Backlight Driver");
+MODULE_LICENSE("GPL");