spi: gpio: Fix spi-gpio to correctly implement sck-idle-input

Formerly, if configured using DT, CS GPIOs were driven from spi.c
and it was possible for CS to be asserted (low) *before* starting
to drive SCK. CS GPIOs have been brought under control of this
driver in both ACPI and DT cases, with a fixup for GPIO polarity.

Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>

drivers/spi/spi-gpio.c

@@ -34,8 +34,9 @@ struct spi_gpio {
 	struct gpio_desc		*sck;
 	struct gpio_desc		*miso;
 	struct gpio_desc		*mosi;
-	bool				sck_idle_input;
 	struct gpio_desc		**cs_gpios;
+	bool				sck_idle_input;
+	bool                            cs_dont_invert;
 };
 
 /*----------------------------------------------------------------------*/
@@ -204,12 +205,18 @@ static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
 			gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);
 	}
 
-	/* Drive chip select line, if we have one */
+	/*
+	 * Drive chip select line, if we have one.
+	 * SPI chip selects are normally active-low, but when
+	 * cs_dont_invert is set, we assume their polarity is
+	 * controlled by the GPIO, and write '1' to assert.
+	 */
 	if (spi_gpio->cs_gpios) {
 		struct gpio_desc *cs = spi_gpio->cs_gpios[spi_get_chipselect(spi, 0)];
+		int val = ((spi->mode & SPI_CS_HIGH) || spi_gpio->cs_dont_invert) ?
+			is_active : !is_active;
 
-		/* SPI chip selects are normally active-low */
+		gpiod_set_value_cansleep(cs, val);
-		gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
 	}
 
 	if (spi_gpio->sck_idle_input && !is_active)
@@ -233,11 +240,14 @@ static int spi_gpio_setup(struct spi_device *spi)
 	/*
 	 * The CS GPIOs have already been
 	 * initialized from the descriptor lookup.
+	 * Here we set them to the non-asserted state.
 	 */
 	if (spi_gpio->cs_gpios) {
 		cs = spi_gpio->cs_gpios[spi_get_chipselect(spi, 0)];
 		if (!spi->controller_state && cs) {
-			ret = gpiod_direction_output(cs, !(spi->mode & SPI_CS_HIGH));
+			ret = gpiod_direction_output(cs,
+							!((spi->mode & SPI_CS_HIGH) ||
+							   spi_gpio->cs_dont_invert));
 			if (ret)
 				return ret;
 		}
@@ -314,31 +324,31 @@ static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
 	return PTR_ERR_OR_ZERO(spi_gpio->sck);
 }
 
-static int spi_gpio_probe_pdata(struct platform_device *pdev,
+/*
-				struct spi_controller *host)
+ * In order to implement "sck-idle-input" (which requires SCK
+ * direction and CS level to be switched in a particular order),
+ * we need to control GPIO chip selects from within this driver.
+ */
+
+static int spi_gpio_probe_get_cs_gpios(struct device *dev,
+				       struct spi_controller *master,
+				       bool gpio_defines_polarity)
 {
-	struct device *dev = &pdev->dev;
-	struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
-	struct spi_gpio *spi_gpio = spi_controller_get_devdata(host);
 	int i;
+	struct spi_gpio *spi_gpio = spi_controller_get_devdata(master);
 
-	if (!pdata)
+	spi_gpio->cs_dont_invert = gpio_defines_polarity;
-		return -ENODEV;
+	spi_gpio->cs_gpios = devm_kcalloc(dev, master->num_chipselect,
-
-	/* It's just one always-selected device, fine to continue */
-	if (!pdata->num_chipselect)
-		return 0;
-
-	host->num_chipselect = pdata->num_chipselect;
-	spi_gpio->cs_gpios = devm_kcalloc(dev, host->num_chipselect,
 					  sizeof(*spi_gpio->cs_gpios),
 					  GFP_KERNEL);
 	if (!spi_gpio->cs_gpios)
 		return -ENOMEM;
 
-	for (i = 0; i < host->num_chipselect; i++) {
+	for (i = 0; i < master->num_chipselect; i++) {
-		spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i,
+		spi_gpio->cs_gpios[i] =
-							     GPIOD_OUT_HIGH);
+			devm_gpiod_get_index(dev, "cs", i,
+					     gpio_defines_polarity ?
+						GPIOD_OUT_LOW : GPIOD_OUT_HIGH);
 		if (IS_ERR(spi_gpio->cs_gpios[i]))
 			return PTR_ERR(spi_gpio->cs_gpios[i]);
 	}
@@ -346,6 +356,24 @@ static int spi_gpio_probe_pdata(struct platform_device *pdev,
 	return 0;
 }
 
+static int spi_gpio_probe_pdata(struct platform_device *pdev,
+				struct spi_controller *host)
+{
+	struct device *dev = &pdev->dev;
+	struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
+
+	if (!pdata)
+		return -ENODEV;
+
+	/*
+	 * The host needs to think there is a chipselect even if not
+	 * connected
+	 */
+	host->num_chipselect = pdata->num_chipselect ?: 1;
+
+	return spi_gpio_probe_get_cs_gpios(dev, host, false);
+}
+
 static int spi_gpio_probe(struct platform_device *pdev)
 {
 	int				status;