Hi Laurent, On Wed, Apr 5, 2017 at 10:45 AM, Laurent Pinchart <laurent.pinch...@ideasonboard.com> wrote: > On Monday 21 Nov 2016 11:59:47 Laurent Pinchart wrote: >> On Monday 21 Nov 2016 10:23:46 Geert Uytterhoeven wrote: >> > On Mon, Nov 21, 2016 at 10:19 AM, Laurent Pinchart wrote: >> >> On Monday 21 Nov 2016 09:36:22 Geert Uytterhoeven wrote: >> >>> On Sat, Nov 19, 2016 at 4:28 AM, Laurent Pinchart wrote: >> >>>> The panel backlight is controlled through a GPIO and a PWM channel. >> >>>> >> >>>> --- a/arch/arm64/boot/dts/renesas/r8a7795-salvator-x.dts >> >>>> +++ b/arch/arm64/boot/dts/renesas/r8a7795-salvator-x.dts >> >>>> @@ -178,6 +178,16 @@ >> >>>> }; >> >>>> }; >> >>>> }; >> >>>> + >> >>>> + backlight: backlight { >> >>>> + compatible = "pwm-backlight"; >> >>>> + pwms = <&pwm1 0 50000>; >> >>>> + >> >>>> + brightness-levels = <256 128 64 16 8 4 0>; >> >>> >> >>> Would it make sense to define more and/or linear levels? >> >> >> >> Possibly, this is pretty arbitrary. Linear levels might not be the best >> >> option given that the human eye doesn't have a linear response to light >> >> power, but we >> > >> > It not only depends on the human eye, but also on the backlight hardware >> > (is the conversion from voltage (L_VBRT) to light linear?). >> >> So we need to specify transfer functions in DT ;-) >> >> >> could certainly have more levels. In that case I'd prefer modifying the >> >> pwm- backlight DT bindings though, and specifying the PWM resolution >> >> instead of discrete levels. >> >> >> >> Note that the LVDS panel backlight PWM control signal is multiplexed >> >> with the external memory A21 signal on the Salvator-X board, with SW5 >> >> selecting which how to route the signal. When using backlight control we >> >> can't access the whole NOR flash anymore, so I'm not sure this patch >> >> should be merged. >> > >> > That NOR flash is also optional, right? >> > My Ex Memory Connector is not populated. >> >> That's correct. The Salvator-X DT file in mainline is just an example >> anyway, and we should pick the most useful peripherals for that purpose. > > Would you like me to include this in my next Salvator-X DT patch series for > upstream merge ?
That's fine for me (CC Simon). Thx! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds