linux-kernel - Re: [PATCH v4 13/13] video: backlight: mt6370: Add Mediatek MT6370 support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAHp75VdXGJtPd_oZPGkS1=DoWjFYxbQu_7Vtfj547QQkpz2KNA@mail.gmail.com>
Date:   Thu, 14 Jul 2022 12:15:58 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     ChiaEn Wu <peterwu.pub@...il.com>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>, Pavel Machek <pavel@....cz>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sebastian Reichel <sre@...nel.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        Helge Deller <deller@....de>,
        ChiaEn Wu <chiaen_wu@...htek.com>,
        Alice Chen <alice_chen@...htek.com>,
        cy_huang <cy_huang@...htek.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        "open list:FRAMEBUFFER LAYER" <linux-fbdev@...r.kernel.org>,
        szuni chen <szunichen@...il.com>
Subject: Re: [PATCH v4 13/13] video: backlight: mt6370: Add Mediatek MT6370 support

On Thu, Jul 14, 2022 at 11:43 AM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Thu, Jul 14, 2022 at 11:27 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Thu, Jul 14, 2022 at 9:13 AM ChiaEn Wu <peterwu.pub@...il.com> wrote:
> > > Andy Shevchenko <andy.shevchenko@...il.com> 於 2022年7月13日 週三 晚上8:07寫道：

...

> > >  * prop_val =  1      -->  1 steps --> b'00
> > >  * prop_val =  2 ~  4 -->  4 steps --> b'01
> > >  * prop_val =  5 ~ 16 --> 16 steps --> b'10
> > >  * prop_val = 17 ~ 64 --> 64 steps --> b'11
> >
> > So, for 1 --> 0, for 2 --> 1, for 5 --> 2, and for 17 --> 3.
> > Now, consider x - 1:
> > 0  ( 0 ) --> 0
> > 1  (2^0) --> 1
> > 4  (2^2) --> 2
> > 16 (2^4) --> 3
> > 64 (2^6) --> ? (but let's consider that the range has been checked already)
> >
> > Since we take the lower limit, it means ffs():
> >
> >   y = (ffs(x - 1) + 1) / 2;
> >
> > Does it work for you?
>
> It wouldn't, because we need to use fls() against it actually.
>
> So,
> 0..1   (-1..0)   --> 0
> 2..4   (1..3)   --> 1
> 5..16  (4..15)  --> 2
> 17..64 (16..63) --> 3
>
> y = x ? ((fls(x - 1) + 1) / 2 : 0;

Okay, I nailed it down, but Daniel is right, it's simpler to have just
conditionals.

y = x >=2 ? __fls(x - 1) / 2 + 1 : 0;


--
With Best Regards,
Andy Shevchenko