[PATCH 2/2 v6] drm/panel: Add driver for Sony ACX424AKP panel

[Linus Walleij]

On Wed, Nov 20, 2019 at 12:53 PM Stephan Gerhold <stephan at gerhold.net> wrote:
> On Thu, Nov 14, 2019 at 02:15:25PM +0100, Linus Walleij wrote:

> > +     /* Calculate the PWM duty cycle in n/256's */
> > +     pwm_ratio = max(((duty_ns * 256) / period_ns) - 1, 1);
> > +     pwm_div = max(1,
> > +                   ((FOSC * period_ns) / 256) /
> > +                   SCALE_FACTOR_NS_DIV_MHZ);
>
> Does this handle the case where brightness = 0 (usually display off)?

Yeah for brightness = 0 it will get duty_ns = 0 and the max()
clause will set the duty cycle to 1.

> I have also often seen code like
>
>         if (bl->props.power != FB_BLANK_UNBLANK ||
>             bl->props.fb_blank != FB_BLANK_UNBLANK ||
>             bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
>                 brightness = 0;
>
> to handle the blanking states. Not sure.

It makes sense to wind down the brightness to minimum when blanking
to save power, but that code seems a bit hairy, so not sure what
is the right thing to do here :/

I guess I could just implement enable/disable for the backlight and
wind it down to 0 in disable and back to whatever brightness is in
enable. But I don't know if that is a good idea since I don't really
enable/disable the backlight (it cannot be disable without shutting
down the display).

Yours,
Linus Walleij