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

[Hans de Goede]

Hi,

On 22-08-16 16:01, Peter Korsgaard wrote:
>>>>>> "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.

Ack, fixed for v2.

>
>
>>  #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

I did not do this because the kernel does not yet
have the backlight(s) described in dts. But that really
is not a good reason to do this, so I've implemented this
and tested it on one of my own A31s tablets, this is also
included in v2.

Regards,

Hans