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

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Message-ID: <CAD=FV=U23+5pcze=6zDTx0dAYF8HTmbR8s8zem93VhgYgaZeGQ@mail.gmail.com>
Date:   Wed, 19 Jun 2019 18:27:55 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        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,

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