linux-kernel - Re: [PATCH v6 09/13] iio: adc: mt6370: Add MediaTek MT6370 support

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Message-ID: <CAHp75VfRZvYA3HJg=LAxXxu26aLSwRGQaED19Bg2d+dZw3RPfw@mail.gmail.com>
Date:   Mon, 25 Jul 2022 10:10:12 +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>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v6 09/13] iio: adc: mt6370: Add MediaTek MT6370 support

On Fri, Jul 22, 2022 at 12:25 PM ChiaEn Wu <peterwu.pub@...il.com> wrote:
>
> From: ChiaEn Wu <chiaen_wu@...htek.com>
>
> MediaTek MT6370 is a SubPMIC consisting of a single cell battery charger
> with ADC monitoring, RGB LEDs, dual channel flashlight, WLED backlight
> driver, display bias voltage supply, one general purpose LDO, and the
> USB Type-C & PD controller complies with the latest USB Type-C and PD
> standards.
>
> Add a support the MT6370 ADC driver for system monitoring, including

support for the

> charger current, voltage, and temperature.

...

> +#define MT6370_AICR_400_mA             0x6
> +#define MT6370_ICHG_500_mA             0x4
> +#define MT6370_ICHG_900_mA             0x8

^^^^ (Note this and read below)

...

> +               reg_val = FIELD_GET(MT6370_AICR_ICHG_MASK, reg_val);
> +               if (reg_val < MT6370_AICR_400_mA)
> +                       *val1 = 3350;
> +               else
> +                       *val1 = 5000;

Here...

...

> +               if (reg_val < MT6370_ICHG_500_mA)
> +                       *val1 = 2375;
> +               else if (reg_val >= MT6370_ICHG_500_mA &&
> +                        reg_val < MT6370_ICHG_900_mA)
> +                       *val1 = 2680;
> +               else
> +                       *val1 = 5000;

...and especially here it is so counterintuitive to have an if-else
chain because the values are not ordered by semantic meaning.

What if the new standard/hardware decides to use 0x7 for 100mA (hypothetically)?

So, please use switch cases or other robust methods.

-- 
With Best Regards,
Andy Shevchenko