linux-kernel - Re: [PATCH 04/10] ARM: dts: rockchip: add startup delay to rk3288-veyron panel-regulators

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Date:   Thu, 20 Jun 2019 14:28:14 +0200
From:   Heiko Stübner <heiko@...ech.de>
To:     Doug Anderson <dianders@...omium.org>
Cc:     "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Yakir Yang <ykk@...k-chips.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] ARM: dts: rockchip: add startup delay to rk3288-veyron panel-regulators

Hi Doug,

Am Donnerstag, 20. Juni 2019, 03:27:55 CEST schrieb Doug Anderson:
> On Wed, Fri, 18 Mar 2016 Heiko Stuebner <heiko@...ech.de> wrote:
> >
> > The panels need a bit of time to actually turn on. If this isn't
> > observed, this results in problems when trying talk to the panels
> > and thus produces detection errors. 100ms seem to be a safe value
> > for the time being.
> >
> > Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> > ---
> >  arch/arm/boot/dts/rk3288-veyron-jaq.dts    | 1 +
> >  arch/arm/boot/dts/rk3288-veyron-jerry.dts  | 1 +
> >  arch/arm/boot/dts/rk3288-veyron-minnie.dts | 1 +
> >  arch/arm/boot/dts/rk3288-veyron-speedy.dts | 1 +
> >  4 files changed, 4 insertions(+)
> 
> I know it was 3 years ago, but any idea how to reproduce the problems
> you were seeing without this patch?  I believe the downstream kernel
> never had any delay like this and I'm not aware of any issues.
>
> I wonder if the need for this extra 100 ms delay is no longer there
> now that we have:
> 
> 3157694d8c7f pwm-backlight: Add support for PWM delays proprieties.
> 5fb5caee92ba pwm-backlight: Enable/disable the PWM before/after LCD
> enable toggle.
> 6d5922dd0d60 ARM: dts: rockchip: set PWM delay backlight settings for Veyron

I just did a non-scientific test on my jerry+minnie and yes, simply
reverting that patch does not seem to affect display bringup and I still
get a prompt.

So I guess we could just revert that patch in light of the changes.
[patches welcome ;-) ]

Heiko