dm: spi: soft_spi: switch to use linux compatible string

1. Support compatible string "spi-gpio" which is used by Linux
   Linux use different bindings, so use UBOOT_COMPAT and
   LINUX_COMPAT to differentiate them.
2. Introduce SPI_MASTER_NO_RX and SPI_MASTER_NO_TX to handle
   no rx or no tx case.
3. Tested on i.MX6 UltraLite board with 74LV595 spi-gpio chip.

Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Przemyslaw Marczak <p.marczak@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/dts/exynos4210-universal_c210.dts

@@ -42,11 +42,11 @@
 	};
 
 	soft-spi {
-		compatible = "u-boot,soft-spi";
-		cs-gpio = <&gpy4 3 0>;
-		sclk-gpio = <&gpy3 1 0>;
-		mosi-gpio = <&gpy3 3 0>;
-		miso-gpio = <&gpy3 0 0>;
+		compatible = "spi-gpio";
+		cs-gpios = <&gpy4 3 0>;
+		gpio-sck = <&gpy3 1 0>;
+		gpio-mosi = <&gpy3 3 0>;
+		gpio-miso = <&gpy3 0 0>;
 		spi-delay-us = <1>;
 		#address-cells = <1>;
 		#size-cells = <0>;

drivers/spi/soft_spi.c

@@ -26,8 +26,12 @@ struct soft_spi_platdata {
 	struct gpio_desc mosi;
 	struct gpio_desc miso;
 	int spi_delay_us;
+	int flags;
 };
 
+#define SPI_MASTER_NO_RX        BIT(0)
+#define SPI_MASTER_NO_TX        BIT(1)
+
 struct soft_spi_priv {
 	unsigned int mode;
 };
@@ -139,14 +143,16 @@ static int soft_spi_xfer(struct udevice *dev, unsigned int bitlen,
 
 		if (!cpha)
 			soft_spi_scl(dev, 0);
-		soft_spi_sda(dev, !!(tmpdout & 0x80));
+		if ((plat->flags & SPI_MASTER_NO_TX) == 0)
+			soft_spi_sda(dev, !!(tmpdout & 0x80));
 		udelay(plat->spi_delay_us);
 		if (cpha)
 			soft_spi_scl(dev, 0);
 		else
 			soft_spi_scl(dev, 1);
 		tmpdin	<<= 1;
-		tmpdin	|= dm_gpio_get_value(&plat->miso);
+		if ((plat->flags & SPI_MASTER_NO_RX) == 0)
+			tmpdin	|= dm_gpio_get_value(&plat->miso);
 		tmpdout	<<= 1;
 		udelay(plat->spi_delay_us);
 		if (cpha)
@@ -208,24 +214,36 @@ static int soft_spi_probe(struct udevice *dev)
 	struct spi_slave *slave = dev_get_parent_priv(dev);
 	struct soft_spi_platdata *plat = dev->platdata;
 	int cs_flags, clk_flags;
+	int ret;
 
 	cs_flags = (slave->mode & SPI_CS_HIGH) ? 0 : GPIOD_ACTIVE_LOW;
 	clk_flags = (slave->mode & SPI_CPOL) ? GPIOD_ACTIVE_LOW : 0;
-	if (gpio_request_by_name(dev, "cs-gpio", 0, &plat->cs,
+
+	if (gpio_request_by_name(dev, "cs-gpios", 0, &plat->cs,
 				 GPIOD_IS_OUT | cs_flags) ||
-	    gpio_request_by_name(dev, "sclk-gpio", 0, &plat->sclk,
-				 GPIOD_IS_OUT | clk_flags) ||
-	    gpio_request_by_name(dev, "mosi-gpio", 0, &plat->mosi,
-				 GPIOD_IS_OUT | GPIOD_IS_OUT_ACTIVE) ||
-	    gpio_request_by_name(dev, "miso-gpio", 0, &plat->miso,
-				 GPIOD_IS_IN))
+	    gpio_request_by_name(dev, "gpio-sck", 0, &plat->sclk,
+				 GPIOD_IS_OUT | clk_flags))
+		return -EINVAL;
+
+	ret = gpio_request_by_name(dev, "gpio-mosi", 0, &plat->mosi,
+				   GPIOD_IS_OUT | GPIOD_IS_OUT_ACTIVE);
+	if (ret)
+		plat->flags |= SPI_MASTER_NO_TX;
+
+	ret = gpio_request_by_name(dev, "gpio-miso", 0, &plat->miso,
+				   GPIOD_IS_IN);
+	if (ret)
+		plat->flags |= SPI_MASTER_NO_RX;
+
+	if ((plat->flags & (SPI_MASTER_NO_RX | SPI_MASTER_NO_TX)) ==
+	    (SPI_MASTER_NO_RX | SPI_MASTER_NO_TX))
 		return -EINVAL;
 
 	return 0;
 }
 
 static const struct udevice_id soft_spi_ids[] = {
-	{ .compatible = "u-boot,soft-spi" },
+	{ .compatible = "spi-gpio" },
 	{ }
 };