linux-kernel - Re: [PATCH v6 11/13] leds: rgb: mt6370: Add MediaTek MT6370 current sink type LED Indicator support

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Date:   Tue, 26 Jul 2022 14:17:44 +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 v6 11/13] leds: rgb: mt6370: Add MediaTek MT6370 current
 sink type LED Indicator support

On Tue, Jul 26, 2022 at 1:46 PM ChiaEn Wu <peterwu.pub@...il.com> wrote:
> On Mon, Jul 25, 2022 at 4:41 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:

...

> > > +struct mt6370_led {
> > > +       union {
> > > +               struct led_classdev isink;
> > > +               struct led_classdev_mc mc;
> > > +       };
> >
> > Where is the field that makes union work?
>
> Just for saving memory space.
> Because these led_classdevs do not be used at the same time.
> Or do you think it would be better to rewrite it as follows?
> -------------------------------------------------------------------------------------
> struct mt6370_led {
>        struct led_classdev isink;
>        struct led_classdev_mc mc;
>        struct mt6370_priv *priv;
>        u32 default_state;
>        u32 index;
> };
> -------------------------------------------------------------------------------------

You obviously didn't get what I'm talking about...
Each union to work properly should have an associated variable that
holds the information of which field of the union is in use. Do you
have such a variable? If not, how does your code know which one to
use? If yes, add a proper comment there.

-- 
With Best Regards,
Andy Shevchenko