Hi Peng,
On Mon, Aug 7, 2017 at 9:27 AM, Peng Fan <peng.fan@xxxxxxx> 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@xxxxxxx>
> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> 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
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