From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from galahad.ideasonboard.com ([185.26.127.97]:49759 "EHLO galahad.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753993AbdDEIpP (ORCPT ); Wed, 5 Apr 2017 04:45:15 -0400 From: Laurent Pinchart To: Geert Uytterhoeven Cc: DRI Development , Linux-Renesas Subject: Re: [PATCH v2 09/13] arm64: dts: r8a7795: salvator-x: Add panel backlight support Date: Wed, 05 Apr 2017 11:45:59 +0300 Message-ID: <18654178.y7VdoJ3ein@avalon> In-Reply-To: <2227128.532ZZ8dc1T@avalon> References: <1479526093-7014-1-git-send-email-laurent.pinchart+renesas@ideasonboard.com> <2227128.532ZZ8dc1T@avalon> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-renesas-soc-owner@vger.kernel.org List-ID: Hi Geert, 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 ? -- Regards, Laurent Pinchart