spi: spi-gpio: Add checks for the dt properties

The bindings assumed that the gpios properties were always there, which
made the NO_TX and NO_RX mode not usable from device tree. Add extra
checks to make sure that the driver can work if either MOSI or MISO is
not used.

Signed-off-by: Maxime Ripard <[e-mail]>
Cc: Mark Brown <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-gpio.c

···
 	if (!pdata)
 		return -ENOMEM;
 
-	pdata->sck = of_get_named_gpio(np, "gpio-sck", 0);
-	pdata->miso = of_get_named_gpio(np, "gpio-miso", 0);
-	pdata->mosi = of_get_named_gpio(np, "gpio-mosi", 0);
+	ret = of_get_named_gpio(np, "gpio-sck", 0);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "gpio-sck property not found\n");
+		goto error_free;
+	}
+	pdata->sck = ret;
+
+	ret = of_get_named_gpio(np, "gpio-miso", 0);
+	if (ret < 0) {
+		dev_info(&pdev->dev, "gpio-miso property not found, switching to no-rx mode\n");
+		pdata->miso = SPI_GPIO_NO_MISO;
+	} else
+		pdata->miso = ret;
+
+	ret = of_get_named_gpio(np, "gpio-mosi", 0);
+	if (ret < 0) {
+		dev_info(&pdev->dev, "gpio-mosi property not found, switching to no-tx mode\n");
+		pdata->mosi = SPI_GPIO_NO_MOSI;
+	} else
+		pdata->mosi = ret;
 
 	ret = of_property_read_u32(np, "num-chipselects", &tmp);
 	if (ret < 0) {