linux-kernel - Re: [PATCH 2/2] gpio: 74x164: handling enable-gpios

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Date:   Mon, 7 Aug 2017 09:36:19 -0300
From:   Fabio Estevam <festevam@...il.com>
To:     Peng Fan <peng.fan@....com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh@...nel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] gpio: 74x164: handling enable-gpios

Hi Peng,

On Mon, Aug 7, 2017 at 9:27 AM, Peng Fan <peng.fan@....com> wrote:
> To 74hc595 and 74lv595, there is an OE(low active) input pin.
> To some boards, this pin is controller by GPIO, so handling
> this pin in driver. When driver probe, use GPIOD_OUT_LOW flag
> when requesting the gpio, so OE is set to low when probe.

Well, this depends of the GPIO polarity.

>
> Signed-off-by: Peng Fan <peng.fan@....com>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> ---
>  drivers/gpio/gpio-74x164.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/gpio/gpio-74x164.c b/drivers/gpio/gpio-74x164.c
> index a6607fa..e44422c 100644
> --- a/drivers/gpio/gpio-74x164.c
> +++ b/drivers/gpio/gpio-74x164.c
> @@ -23,6 +23,7 @@ struct gen_74x164_chip {
>         struct gpio_chip        gpio_chip;
>         struct mutex            lock;
>         u32                     registers;
> +       struct gpio_desc        *enable_gpio;
>         /*
>          * Since the registers are chained, every byte sent will make
>          * the previous byte shift to the next register in the
> @@ -142,6 +143,12 @@ static int gen_74x164_probe(struct spi_device *spi)
>         chip->gpio_chip.parent = &spi->dev;
>         chip->gpio_chip.owner = THIS_MODULE;
>
> +       chip->enable_gpio = devm_gpiod_get(&spi->dev, "enable", GPIOD_OUT_LOW);

It would be better to use devm_gpiod_get_optional instead.

> +       if (IS_ERR(chip->enable_gpio)) {
> +               dev_dbg(&spi->dev, "No enable-gpios property\n");
> +               chip->enable_gpio = NULL;
> +       }
> +
>         mutex_init(&chip->lock);
>
>         ret = __gen_74x164_write_config(chip);
> @@ -164,6 +171,8 @@ static int gen_74x164_remove(struct spi_device *spi)
>  {
>         struct gen_74x164_chip *chip = spi_get_drvdata(spi);
>
> +       if (chip->enable_gpio)
> +               gpiod_set_value(chip->enable_gpio, 0);

It would be better to use the cansleep variant instead.

Actually I have worked on adding this optional property, but haven't
submitted yet:
https://pastebin.com/u839DVD3