[U-Boot] [PATCH] sunxi: display: Use PWM to drive backlight where applicable

[Peter Korsgaard]

>>>>> "Hans" == Hans de Goede <hdegoede at redhat.com> writes:

 > 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.

Nice!

 > Signed-off-by: Hans de Goede <hdegoede at redhat.com>
 > ---
 >  arch/arm/include/asm/arch-sunxi/cpu_sun4i.h |  1 +
 >  arch/arm/include/asm/arch-sunxi/gpio.h      |  1 +
 >  arch/arm/include/asm/arch-sunxi/pwm.h       | 27 +++++++++++++++++++++++++++
 >  drivers/video/sunxi_display.c               | 12 +++++++++++-
 >  4 files changed, 40 insertions(+), 1 deletion(-)
 >  create mode 100644 arch/arm/include/asm/arch-sunxi/pwm.h

 > diff --git a/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h b/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h
 > index cd009d7..a5f396e 100644
 > --- a/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h
 > +++ b/arch/arm/include/asm/arch-sunxi/cpu_sun4i.h
 > @@ -76,6 +76,7 @@
 >  #define SUNXI_INTC_BASE			0x01c20400
 >  #define SUNXI_PIO_BASE			0x01c20800
 >  #define SUNXI_TIMER_BASE		0x01c20c00
 > +#define SUNXI_PWM_BASE			0x01c20e00
 >  #define SUNXI_SPDIF_BASE		0x01c21000
 >  #define SUNXI_AC97_BASE			0x01c21400
 >  #define SUNXI_IR0_BASE			0x01c21800
 > diff --git a/arch/arm/include/asm/arch-sunxi/gpio.h b/arch/arm/include/asm/arch-sunxi/gpio.h
 > index bff7d14..ef426ae 100644
 > --- a/arch/arm/include/asm/arch-sunxi/gpio.h
 > +++ b/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

Using this define for the ! SUN4I / SUN5I case is a bit icky (even if
they today happen to be the same numerical value). Perhaps introduce a
SUNXI_PWM_MODE indirection like you do for SUNXI_PWM_PIN0 would be
nicer.


>  #define SUN4I_GPB_TWI0		2
 >  #define SUN4I_GPB_TWI1		2
 >  #define SUN5I_GPB_TWI1		2
 > diff --git a/arch/arm/include/asm/arch-sunxi/pwm.h b/arch/arm/include/asm/arch-sunxi/pwm.h
 > new file mode 100644
 > index 0000000..ec997a6
 > --- /dev/null
 > +++ b/arch/arm/include/asm/arch-sunxi/pwm.h
 > @@ -0,0 +1,27 @@
 > +/*
 > + * (C) Copyright 2016 Hans de Goede <hdegoede at 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)
 > +#endif
 > +

This should afaik work for sun6i as well if you add:

#if defined CONFIG_MACH_SUN6I
#define SUNXI_PWM_PIN0  SUNXI_GPH(13)
#endif

E.G. the Yones Toptech BS1078v2 uses this.

I'll try to find some time to test it.

-- 
Bye, Peter Korsgaard