spi: gpio: Add sck-idle-input property

The sck-idle-input property indicates that the spi-gpio driver should
return the SCK line to an input when the chip select signals are
inactive.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
index d8db456..af9cef6 100644 (file)
--- a/drivers/spi/spi-gpio.c
+++ b/drivers/spi/spi-gpio.c
@@ -34,6 +34,7 @@ struct spi_gpio {
        struct gpio_desc                *sck;
        struct gpio_desc                *miso;
        struct gpio_desc                *mosi;
+       bool                            sck_idle_input;
        struct gpio_desc                **cs_gpios;
 };
 
@@ -224,8 +225,12 @@ static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
        struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
 
        /* set initial clock line level */
-       if (is_active)
-               gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);
+       if (is_active) {
+               if (spi_gpio->sck_idle_input)
+                       gpiod_direction_output(spi_gpio->sck, spi->mode & SPI_CPOL);
+               else
+                       gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);
+       }
 
        /* Drive chip select line, if we have one */
        if (spi_gpio->cs_gpios) {
@@ -234,6 +239,9 @@ static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
                /* SPI chip selects are normally active-low */
                gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
        }
+
+       if (spi_gpio->sck_idle_input && !is_active)
+               gpiod_direction_input(spi_gpio->sck);
 }
 
 static int spi_gpio_setup(struct spi_device *spi)
@@ -322,6 +330,7 @@ static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
        if (IS_ERR(spi_gpio->miso))
                return PTR_ERR(spi_gpio->miso);
 
+       spi_gpio->sck_idle_input = device_property_read_bool(dev, "sck-idle-input");
        spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
        return PTR_ERR_OR_ZERO(spi_gpio->sck);
 }