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Date:   Mon, 9 Oct 2023 17:02:25 +0300
From:   Dmitry Rokosov <ddrokosov@salutedevices.com>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
CC:     <lee@kernel.org>, <pavel@ucw.cz>, <robh+dt@kernel.org>,
        <krzysztof.kozlowski+dt@linaro.org>, <conor+dt@kernel.org>,
        <kernel@sberdevices.ru>, <rockosov@gmail.com>,
        <devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-leds@vger.kernel.org>,
        George Stark <gnstark@salutedevices.com>
Subject: Re: [PATCH v1 09/11] leds: aw200xx: improve autodim calculation
 method
Message-ID: <20231009140225.gj7vkmmio5xfvtnk@CAB-WSD-L081021>
References: <20231006160437.15627-1-ddrokosov@salutedevices.com>
 <20231006160437.15627-10-ddrokosov@salutedevices.com>
 <CAHp75VcntHXe31H8C9GcGhc+HRA-gZjtD=uibMMYN-FS254RJw@mail.gmail.com>
 <20231009131808.lzri7z2nvcmkfuu3@CAB-WSD-L081021>
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On Mon, Oct 09, 2023 at 04:18:08PM +0300, Dmitry Rokosov wrote:
> On Fri, Oct 06, 2023 at 09:03:47PM +0300, Andy Shevchenko wrote:
> > On Fri, Oct 6, 2023 at 7:05 PM Dmitry Rokosov
> > <ddrokosov@salutedevices.com> wrote:
> > >
> > > From: George Stark <gnstark@salutedevices.com>
> > >
> > > use DIV_ROUND_UP instead of coarse div
> > 
> > Please, respect English grammar and punctuation.
> > Refer to macros and functions as func() (note the parentheses).
> > 
> > ...
> > 
> > >  #define AW200XX_REG_DIM2FADE(x) ((x) + 1)
> > > +#define AW200XX_REG_FADE2DIM(fade) \
> > > +       DIV_ROUND_UP((fade) * AW200XX_DIM_MAX, AW200XX_FADE_MAX)
> > 
> > Have you checked if the overflow is _now_ possible (compiling on
> > 32-bit platforms as well)?
> 
> I suppose we shouldn't carry on about overflow here because the value of
> fade cannot exceed 255, and DIM_MAX is set at 63
> 
> You can find maximum values of fade and dim in the aw200xx driver
> header:
> 
> #define AW200XX_DIM_MAX                  (BIT(6) - 1)
> #define AW200XX_FADE_MAX                 (BIT(8) - 1)

I agree that checking if the fade is not greater than FADE_MAX will not
be excessive. The LED subsystem is capable of sending brightness levels
higher than 255

-- 
Thank you,
Dmitry