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

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Message-ID: <20210111110407.GR1551@shell.armlinux.org.uk>
Date:   Mon, 11 Jan 2021 11:04:07 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
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>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.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 01:44:28PM +0800, DENG Qingfang wrote:
> +static int
> +mt7530_gpio_direction_output(struct gpio_chip *gc, unsigned int offset, int value)
> +{
> +	struct mt7530_priv *priv = gpiochip_get_data(gc);
> +	u32 bit = mt7530_gpio_to_bit(offset);
> +
> +	mt7530_set(priv, MT7530_LED_GPIO_DIR, bit);
> +	mt7530_set(priv, MT7530_LED_GPIO_OE, bit);
> +	mt7530_gpio_set(gc, offset, value);

FYI, Documentation/driver-api/gpio/consumer.rst says:

  For output GPIOs, the value provided becomes the initial output value.
  This helps avoid signal glitching during system startup.

Setting the pin to be an output, and then setting its initial value
does not avoid the glitch. You may wish to investigate whether you
can set the value before setting the pin as an output to avoid this
issue.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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