backlight: add support for Pandora backlight

Add support for pandora (openpandora.org) backlight.

It might look like all this could be done using pwm_bl.c instead, but
there is a need of special programming sequence when turning on the LED
driver chip or else it will misbehave.  Doing this using pwm_bl.c would
require to use some register programming and pwm functions from platform
code, and ARM maintainers are allergic to driver-like code in /arch/arm
nowadays.  The PMIC PWM driver is currently missing too, so pwm_bl.c
can't be used anyway.
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/Kconfig

@@ -348,6 +348,13 @@ config BACKLIGHT_OT200
 	  To compile this driver as a module, choose M here: the module will be
 	  called ot200_bl.
 
+config BACKLIGHT_PANDORA
+	tristate "Backlight driver for Pandora console"
+	depends on TWL4030_CORE
+	help
+	  If you have a Pandora console, say Y to enable the
+	  backlight driver.
+
 endif # BACKLIGHT_CLASS_DEVICE
 
 endif # BACKLIGHT_LCD_SUPPORT

drivers/video/backlight/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_BACKLIGHT_HP680)	+= hp680_bl.o
 obj-$(CONFIG_BACKLIGHT_LOCOMO)	+= locomolcd.o
 obj-$(CONFIG_BACKLIGHT_LP855X)	+= lp855x_bl.o
 obj-$(CONFIG_BACKLIGHT_OMAP1)	+= omap1_bl.o
+obj-$(CONFIG_BACKLIGHT_PANDORA)	+= pandora_bl.o
 obj-$(CONFIG_BACKLIGHT_PROGEAR) += progear_bl.o
 obj-$(CONFIG_BACKLIGHT_CARILLO_RANCH) += cr_bllcd.o
 obj-$(CONFIG_BACKLIGHT_PWM)	+= pwm_bl.o

drivers/video/backlight/pandora_bl.c

+/*
+ * Backlight driver for Pandora handheld.
+ * Pandora uses TWL4030 PWM0 -> TPS61161 combo for control backlight.
+ * Based on pwm_bl.c
+ *
+ * Copyright 2009,2012 Gražvydas Ignotas <notasas@gmail.com>
+ *
+ * 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/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/delay.h>
+#include <linux/fb.h>
+#include <linux/backlight.h>
+#include <linux/i2c/twl.h>
+#include <linux/err.h>
+
+#define TWL_PWM0_ON		0x00
+#define TWL_PWM0_OFF		0x01
+
+#define TWL_INTBR_GPBR1		0x0c
+#define TWL_INTBR_PMBR1		0x0d
+
+#define TWL_PMBR1_PWM0_MUXMASK	0x0c
+#define TWL_PMBR1_PWM0		0x04
+#define PWM0_CLK_ENABLE		BIT(0)
+#define PWM0_ENABLE		BIT(2)
+
+/* range accepted by hardware */
+#define MIN_VALUE 9
+#define MAX_VALUE 63
+#define MAX_USER_VALUE (MAX_VALUE - MIN_VALUE)
+
+#define PANDORABL_WAS_OFF BL_CORE_DRIVER1
+
+static int pandora_backlight_update_status(struct backlight_device *bl)
+{
+	int brightness = bl->props.brightness;
+	u8 r;
+
+	if (bl->props.power != FB_BLANK_UNBLANK)
+		brightness = 0;
+	if (bl->props.state & BL_CORE_FBBLANK)
+		brightness = 0;
+	if (bl->props.state & BL_CORE_SUSPENDED)
+		brightness = 0;
+
+	if ((unsigned int)brightness > MAX_USER_VALUE)
+		brightness = MAX_USER_VALUE;
+
+	if (brightness == 0) {
+		if (bl->props.state & PANDORABL_WAS_OFF)
+			goto done;
+
+		/* first disable PWM0 output, then clock */
+		twl_i2c_read_u8(TWL4030_MODULE_INTBR, &r, TWL_INTBR_GPBR1);
+		r &= ~PWM0_ENABLE;
+		twl_i2c_write_u8(TWL4030_MODULE_INTBR, r, TWL_INTBR_GPBR1);
+		r &= ~PWM0_CLK_ENABLE;
+		twl_i2c_write_u8(TWL4030_MODULE_INTBR, r, TWL_INTBR_GPBR1);
+
+		goto done;
+	}
+
+	if (bl->props.state & PANDORABL_WAS_OFF) {
+		/*
+		 * set PWM duty cycle to max. TPS61161 seems to use this
+		 * to calibrate it's PWM sensitivity when it starts.
+		 */
+		twl_i2c_write_u8(TWL4030_MODULE_PWM0, MAX_VALUE,
+					TWL_PWM0_OFF);
+
+		/* first enable clock, then PWM0 out */
+		twl_i2c_read_u8(TWL4030_MODULE_INTBR, &r, TWL_INTBR_GPBR1);
+		r &= ~PWM0_ENABLE;
+		r |= PWM0_CLK_ENABLE;
+		twl_i2c_write_u8(TWL4030_MODULE_INTBR, r, TWL_INTBR_GPBR1);
+		r |= PWM0_ENABLE;
+		twl_i2c_write_u8(TWL4030_MODULE_INTBR, r, TWL_INTBR_GPBR1);
+
+		/*
+		 * TI made it very easy to enable digital control, so easy that
+		 * it often triggers unintentionally and disabes PWM control,
+		 * so wait until 1 wire mode detection window ends.
+		 */
+		usleep_range(2000, 10000);
+	}
+
+	twl_i2c_write_u8(TWL4030_MODULE_PWM0, MIN_VALUE + brightness,
+				TWL_PWM0_OFF);
+
+done:
+	if (brightness != 0)
+		bl->props.state &= ~PANDORABL_WAS_OFF;
+	else
+		bl->props.state |= PANDORABL_WAS_OFF;
+
+	return 0;
+}
+
+static int pandora_backlight_get_brightness(struct backlight_device *bl)
+{
+	return bl->props.brightness;
+}
+
+static const struct backlight_ops pandora_backlight_ops = {
+	.options	= BL_CORE_SUSPENDRESUME,
+	.update_status	= pandora_backlight_update_status,
+	.get_brightness	= pandora_backlight_get_brightness,
+};
+
+static int pandora_backlight_probe(struct platform_device *pdev)
+{
+	struct backlight_properties props;
+	struct backlight_device *bl;
+	u8 r;
+
+	memset(&props, 0, sizeof(props));
+	props.max_brightness = MAX_USER_VALUE;
+	props.type = BACKLIGHT_RAW;
+	bl = backlight_device_register(pdev->name, &pdev->dev,
+			NULL, &pandora_backlight_ops, &props);
+	if (IS_ERR(bl)) {
+		dev_err(&pdev->dev, "failed to register backlight\n");
+		return PTR_ERR(bl);
+	}
+
+	platform_set_drvdata(pdev, bl);
+
+	/* 64 cycle period, ON position 0 */
+	twl_i2c_write_u8(TWL4030_MODULE_PWM0, 0x80, TWL_PWM0_ON);
+
+	bl->props.state |= PANDORABL_WAS_OFF;
+	bl->props.brightness = MAX_USER_VALUE;
+	backlight_update_status(bl);
+
+	/* enable PWM function in pin mux */
+	twl_i2c_read_u8(TWL4030_MODULE_INTBR, &r, TWL_INTBR_PMBR1);
+	r &= ~TWL_PMBR1_PWM0_MUXMASK;
+	r |= TWL_PMBR1_PWM0;
+	twl_i2c_write_u8(TWL4030_MODULE_INTBR, r, TWL_INTBR_PMBR1);
+
+	return 0;
+}
+
+static int pandora_backlight_remove(struct platform_device *pdev)
+{
+	struct backlight_device *bl = platform_get_drvdata(pdev);
+	backlight_device_unregister(bl);
+	return 0;
+}
+
+static struct platform_driver pandora_backlight_driver = {
+	.driver		= {
+		.name	= "pandora-backlight",
+		.owner	= THIS_MODULE,
+	},
+	.probe		= pandora_backlight_probe,
+	.remove		= pandora_backlight_remove,
+};
+
+module_platform_driver(pandora_backlight_driver);
+
+MODULE_AUTHOR("Gražvydas Ignotas <notasas@gmail.com>");
+MODULE_DESCRIPTION("Pandora Backlight Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:pandora-backlight");