Re: [PATCH] Revert "ARM: dts: rockchip: set PWM delay backlight settings for Minnie"

From: Pavel Machek <pavel@ucw.cz>
To: Matthias Kaehlcke <mka@chromium.org>
Cc: Heiko Stuebner <heiko@sntech.de>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Enric Balletbo i Serra <enric.balletbo@collabora.com>,
	Douglas Anderson <dianders@chromium.org>
Subject: Re: [PATCH] Revert "ARM: dts: rockchip: set PWM delay backlight settings for Minnie"
Date: Tue, 18 Jun 2019 14:02:21 +0200	[thread overview]
Message-ID: <20190618120221.GA20524@amd> (raw)
In-Reply-To: <20190617161625.GR137143@google.com>

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On Mon 2019-06-17 09:16:25, Matthias Kaehlcke wrote:
> Hi Pavel,
> 
> On Sun, Jun 16, 2019 at 05:41:43PM +0200, Pavel Machek wrote:
> > Hi!
> > 
> > > This reverts commit 288ceb85b505c19abe1895df068dda5ed20cf482.
> > > 
> > > According to the commit message the AUO B101EAN01 panel on minnie
> > > requires a PWM delay of 200 ms, however this is not what the
> > > datasheet says. The datasheet mentions a *max* delay of 200 ms
> > > for T2 ("delay from LCDVDD to black video generation") and T3
> > > ("delay from LCDVDD to HPD high"), which aren't related to the
> > > PWM. The backlight power sequence does not specify min/max
> > > constraints for T15 (time from PWM on to BL enable) or T16
> > > (time from BL disable to PWM off).
> > > 
> > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > > ---
> > > Enric, if you think I misinterpreted the datasheet please holler!
> > 
> > Was this tested?
> 
> I performed limited manually testing.
> 
> minnie ships with the Chrome OS 3.14 downstream, which doesn't include
> this delay, to my knowledge there are no open display related bugs for
> minnie. One could argue that a the configuration without the delay was
> widely field tested
> 
> > Does patch being reverted actually break anything?
> 
> To my knowledge it doesn't really break anything, however there is a
> short user perceptible delay between switching on the LCD and
> switching on the backlight. It's not the end of the world, but if it's
> not actually needed better avoid it.
> 
> > If so, cc stable?
> 
> I guess this is an edge case, were you could go either way. I'm fine
> with respinning and cc-ing stable.

Ok, if it is just a small delay, stable probably does not need to be
involved.

Thanks,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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