linux-kernel - Re: [PATCH v6 1/5] pwm-backlight: enable/disable the PWM before/after LCD enable toggle.

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Message-ID: <CAFqH_52fFLhuj6gkRNJsPozNfLSAKd0OpQKMjrdhqHRYU4xZ3Q@mail.gmail.com>
Date:   Mon, 26 Mar 2018 16:40:21 +0200
From:   Enric Balletbo Serra <eballetbo@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Thierry Reding <thierry.reding@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        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>,
        linux-leds@...r.kernel.org,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        kernel@...labora.com
Subject: Re: [PATCH v6 1/5] pwm-backlight: enable/disable the PWM before/after
 LCD enable toggle.

Hi Pavel,

2018-03-26 12:42 GMT+02:00 Pavel Machek <pavel@....cz>:
> On Mon 2018-03-26 11:52:09, Enric Balletbo i Serra wrote:
>> Before this patch the enable signal was set before the PWM signal and
>> vice-versa on power off. This sequence is wrong, at least, it is on
>> the different panels datasheets that I checked, so I inverted the sequence
>> to follow the specs.
>>
>> For reference the following panels have the mentioned sequence:
>>   - N133HSE-EA1 (Innolux)
>>   - N116BGE (Innolux)
>>   - N156BGE-L21 (Innolux)
>>   - B101EAN0 (Auo)
>>   - B101AW03 (Auo)
>>   - LTN101NT05 (Samsung)
>>   - CLAA101WA01A (Chunghwa)
>
> Ok, but this changes behaviour for other panels, too. Are you sure you
> are not breaking one of those?

I can't say that I am 100% sure because I didn't find all the
datasheets of all the panels supported in the kernel. But all the
datasheets I checked specifies this sequence as valid. In general I
think that doesn't really matter, but I know that at least the
B116XTN02 panel requires enable first the PWM, wait 10ms and then
enable BL_EN to avoid garbage. So the other way around is not valid
for this panel. That's the reason for this patchset.

If anyone knows a panel that says the contrary, please let me know and
I'll try to rework the patches to satisfy both requirements.

Regards,
 Enric


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