sunxi: display: Use PWM to drive backlight where applicable

When the backlight's pwm input is connected to a pwm output of the SoC,
actually use pwm to drive the backlight.

The mean reason for doing this is to fix the backlight turning off
for aprox. 1 second while the kernel is booting. This is caused by
the kernel actually using pwm to drive the backlight, so that it
can dim the backlight. First the pwm driver loads and switches the
pinmux for the pin driving the backlight's pwm input to the pwm
controller. Then about 1s later the actual backlight driver loads
and tells the pwm driver to actually update the pwm settings, which
have a power-on-reset value of "off".

An additional advantage is that this allows us to initatiate the
backlight at 80%, which is the kernel default, avoiding a brightness
change while the kernel loads.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed by: Peter Korsgaard <peter@korsgaard.com>

arch/arm/include/asm/arch-sunxi/cpu_sun4i.h

@@ -76,8 +76,15 @@
 #define SUNXI_INTC_BASE			0x01c20400
 #define SUNXI_PIO_BASE			0x01c20800
 #define SUNXI_TIMER_BASE		0x01c20c00
+#ifndef CONFIG_SUNXI_GEN_SUN6I
+#define SUNXI_PWM_BASE			0x01c20e00
+#endif
 #define SUNXI_SPDIF_BASE		0x01c21000
+#ifdef CONFIG_SUNXI_GEN_SUN6I
+#define SUNXI_PWM_BASE			0x01c21400
+#else
 #define SUNXI_AC97_BASE			0x01c21400
+#endif
 #define SUNXI_IR0_BASE			0x01c21800
 #define SUNXI_IR1_BASE			0x01c21c00
 

arch/arm/include/asm/arch-sunxi/gpio.h

@@ -150,6 +150,7 @@ enum sunxi_gpio_number {
 #define SUN6I_GPA_SDC3		4
 #define SUN8I_H3_GPA_UART0	2
 
+#define SUN4I_GPB_PWM		2
 #define SUN4I_GPB_TWI0		2
 #define SUN4I_GPB_TWI1		2
 #define SUN5I_GPB_TWI1		2
@@ -186,6 +187,8 @@ enum sunxi_gpio_number {
 #define SUN6I_GPG_TWI3		2
 #define SUN5I_GPG_UART1		4
 
+#define SUN6I_GPH_PWM		2
+#define SUN8I_GPH_PWM		2
 #define SUN4I_GPH_SDC1		5
 #define SUN6I_GPH_TWI0		2
 #define SUN8I_GPH_TWI0		2

arch/arm/include/asm/arch-sunxi/pwm.h

@@ -0,0 +1,34 @@
+/*
+ * (C) Copyright 2016 Hans de Goede <hdegoede@redhat.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _SUNXI_PWM_H
+#define _SUNXI_PWM_H
+
+#define SUNXI_PWM_CTRL_REG		(SUNXI_PWM_BASE + 0)
+#define SUNXI_PWM_CH0_PERIOD		(SUNXI_PWM_BASE + 4)
+
+#define SUNXI_PWM_CTRL_PRESCALE0(x)	((x) & 0xf)
+#define SUNXI_PWM_CTRL_ENABLE0		(0x5 << 4)
+#define SUNXI_PWM_CTRL_POLARITY0(x)	((x) << 5)
+
+#define SUNXI_PWM_PERIOD_80PCT		0x04af03c0
+
+#if defined CONFIG_MACH_SUN4I || defined CONFIG_MACH_SUN5I
+#define SUNXI_PWM_PIN0			SUNXI_GPB(2)
+#define SUNXI_PWM_MUX			SUN4I_GPB_PWM
+#endif
+
+#if defined CONFIG_MACH_SUN6I
+#define SUNXI_PWM_PIN0			SUNXI_GPH(13)
+#define SUNXI_PWM_MUX			SUN6I_GPH_PWM
+#endif
+
+#if defined CONFIG_MACH_SUN8I_A23 || defined CONFIG_MACH_SUN8I_A33
+#define SUNXI_PWM_PIN0			SUNXI_GPH(0)
+#define SUNXI_PWM_MUX			SUN8I_GPH_PWM
+#endif
+
+#endif

drivers/video/sunxi_display.c

@@ -12,6 +12,7 @@
 #include <asm/arch/clock.h>
 #include <asm/arch/display.h>
 #include <asm/arch/gpio.h>
+#include <asm/arch/pwm.h>
 #include <asm/global_data.h>
 #include <asm/gpio.h>
 #include <asm/io.h>
@@ -743,6 +744,16 @@ static void sunxi_lcdc_backlight_enable(void)
 		gpio_direction_output(pin, 1);
 
 	pin = sunxi_name_to_gpio(CONFIG_VIDEO_LCD_BL_PWM);
+#ifdef SUNXI_PWM_PIN0
+	if (pin == SUNXI_PWM_PIN0) {
+		writel(SUNXI_PWM_CTRL_POLARITY0(PWM_ON) |
+		       SUNXI_PWM_CTRL_ENABLE0 |
+		       SUNXI_PWM_CTRL_PRESCALE0(0xf), SUNXI_PWM_CTRL_REG);
+		writel(SUNXI_PWM_PERIOD_80PCT, SUNXI_PWM_CH0_PERIOD);
+		sunxi_gpio_set_cfgpin(pin, SUNXI_PWM_MUX);
+		return;
+	}
+#endif
 	if (pin >= 0)
 		gpio_direction_output(pin, PWM_ON);
 }