linux-kernel - Re: [PATCH net-next 2/2] drivers: net: dsa: mt7530: MT7530 optional GPIO support

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Date:   Mon, 18 Jan 2021 15:55:30 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Russell King <linux@...linux.org.uk>,
        netdev <netdev@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        René van Dorst <opensource@...rst.com>,
        Frank Wunderlich <frank-w@...lic-files.de>
Subject: Re: [PATCH net-next 2/2] drivers: net: dsa: mt7530: MT7530 optional
 GPIO support

On Mon, Jan 11, 2021 at 6:46 AM DENG Qingfang <dqfext@...il.com> wrote:

> MT7530's LED controller can drive up to 15 LED/GPIOs.
>
> Add support for GPIO control and allow users to use its GPIOs by
> setting gpio-controller property in device tree.
>
> Signed-off-by: DENG Qingfang <dqfext@...il.com>

Double-check the initial output conditions as indicated by
Russell, if you really want to be thorough, use an oscilloscope
but check the specs at least.

> +static u32
> +mt7530_gpio_to_bit(unsigned int offset)
> +{
> +       return BIT(offset + offset / 3);
> +}

So for offset 0..14 this becomes bits
0, 1, 2, 4, 5, 6, 8, 9, 10, 12  ... 18

What is the logic in this and is it what you intend?
Please add a comment explaining what the offset is supposed
to become for offsets 0..14 and why.

> +       gc->ngpio = 15;

And it really IS 15 not 16? Not that I know network equipment
very well...

Yours,
Linus Walleij