linux-kernel - Re: [PATCH v3 5/5] ARM: dts: rockchip: set PWM delay backlight settings for Minnie

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Date:   Thu, 20 Jul 2017 12:03:40 +0200
From:   Enric Balletbo Serra <eballetbo@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        linux-fbdev@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Guenter Roeck <groeck@...omium.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v3 5/5] ARM: dts: rockchip: set PWM delay backlight
 settings for Minnie

Pavel,

2017-07-20 10:10 GMT+02:00 Pavel Machek <pavel@....cz>:
> On Mon 2017-07-17 23:28:11, Enric Balletbo i Serra wrote:
>> The minnie devices comes with an AUO B101EAN01 panel which is different
>> from default veyron devices, thus the power on/off timing sequence is
>> slightly different. The datasheet specifies a pwm delay of 200 ms, so
>> update the PMW delay proprieties accordingly.
>
> Wait a wait a moment!
>
>> --- a/arch/arm/boot/dts/rk3288-veyron-minnie.dts
>> +++ b/arch/arm/boot/dts/rk3288-veyron-minnie.dts
>> @@ -123,6 +123,8 @@
>>                       240 241 242 243 244 245 246 247
>>                       248 249 250 251 252 253 254 255>;
>>       power-supply = <&backlight_regulator>;
>> +     post-pwm-on-delay-us = <20000>;
>
> -us = <20 000>;
>
> This is not 200 msec.
>

Oops, good catch.

> Plus, it is quite anti-social to do udelay(200 000).
>
> Plus, it is very anti-socifal to use udelay_range(200msec,
> 400msec).
>
> Whoever told you udelay_range is good thing to use -- it is not, and
> it is certainly not worth making user wait 200msec more!
>

Checked again some datasheets and seems that or not require a delay or
the delays are 10ms+, so according to [1] I'll use msleep instead.

[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Thanks,
 Enric

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