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

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Message-ID: <49b1d68c-2f16-2efd-ae24-2e2bd95a094b@salutedevices.com>
Date:   Tue, 17 Oct 2023 00:22:51 +0300
From:   George Stark <gnstark@...utedevices.com>
To:     Dmitry Rokosov <ddrokosov@...utedevices.com>,
        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>
Subject: Re: [PATCH v1 09/11] leds: aw200xx: improve autodim calculation
 method



On 10/9/23 17:02, Dmitry Rokosov wrote:
> 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
> 

Probably we should set max_brightness to AW200XX_FADE_MAX in 
led_classdev when adding leds.

-- 
Best regards
George