linux-kernel - Re: [PATCH v1 09/11] leds: aw200xx: improve autodim calculation method

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Message-ID: <20231009140225.gj7vkmmio5xfvtnk@CAB-WSD-L081021>
Date:   Mon, 9 Oct 2023 17:02:25 +0300
From:   Dmitry Rokosov <ddrokosov@...utedevices.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     <lee@...nel.org>, <pavel@....cz>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <kernel@...rdevices.ru>, <rockosov@...il.com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-leds@...r.kernel.org>,
        George Stark <gnstark@...utedevices.com>
Subject: Re: [PATCH v1 09/11] leds: aw200xx: improve autodim calculation
 method

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@...utedevices.com> wrote:
> > >
> > > From: George Stark <gnstark@...utedevices.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