Add display PWM driver support to modify backlight for MT8173 and MT6595.
The PWM has one channel to control the brightness of the display.
When the (high_width / period) is closer to 1, the screen is brighter; otherwise, it is darker.

Change-Id: Ie85b295e2dddd90b4163af1c906df977f79b59d6
Signed-off-by: YH Huang <redacted>
---
 drivers/pwm/Kconfig        |  10 ++
 drivers/pwm/Makefile       |   1 +
 drivers/pwm/pwm-mtk-disp.c | 256 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 267 insertions(+)
 create mode 100644 drivers/pwm/pwm-mtk-disp.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index b1541f4..90e3c079 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig

@@ -211,6 +211,16 @@ config PWM_LPSS_PLATFORM
          To compile this driver as a module, choose M here: the module
          will be called pwm-lpss-platform.

+config PWM_MTK_DISP
+       tristate "MediaTek display PWM driver"
+       depends on HAS_IOMEM

+       help
+         Generic PWM framework driver for MediaTek disp-pwm device.
+         The PWM is used to control the backlight brightness for display.
+
+         To compile this driver as a module, choose M here: the module
+         will be called pwm-mtk-disp.
+
 config PWM_MXS
        tristate "Freescale MXS PWM support"
        depends on ARCH_MXS && OF

diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index ec50eb5..99c9e75 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile

@@ -18,6 +18,7 @@ obj-$(CONFIG_PWM_LPC32XX)     += pwm-lpc32xx.o
 obj-$(CONFIG_PWM_LPSS)         += pwm-lpss.o
 obj-$(CONFIG_PWM_LPSS_PCI)     += pwm-lpss-pci.o
 obj-$(CONFIG_PWM_LPSS_PLATFORM)        += pwm-lpss-platform.o
+obj-$(CONFIG_PWM_MTK_DISP)     += pwm-mtk-disp.o
 obj-$(CONFIG_PWM_MXS)          += pwm-mxs.o
 obj-$(CONFIG_PWM_PCA9685)      += pwm-pca9685.o
 obj-$(CONFIG_PWM_PUV3)         += pwm-puv3.o

diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c
new file mode 100644
index 0000000..fb3a42e
--- /dev/null
+++ b/drivers/pwm/pwm-mtk-disp.c

@@ -0,0 +1,256 @@
+/*
+ * MediaTek display pulse-width-modulation controller driver.
+ * Copyright (c) 2015 MediaTek Inc.
+ * Author: YH Huang <yh.huang@mediatek.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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pwm.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#define DISP_PWM_EN            0x0
+#define PWM_ENABLE_MASK                0x1