iio: adc: at91-sama5d2_adc: fix probe error on missing trigger property

This fix allows platforms to probe correctly even if the
trigger edge property is missing. The hardware trigger
will no longer be registered in the sybsystem
Preserves backwards compatibility with the support that
was in the driver before the hardware trigger.

https://storage.kernelci.org/mainline/master/v4.14-rc2-255-g74d83ec2b734/arm/sama5_defconfig/lab-free-electrons/boot-at91-sama5d2_xplained.txt

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Fixes: 5e1a1da0f ("iio: adc: at91-sama5d2_adc: add hw trigger and buffer support")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91-sama5d2_adc.c

@@ -225,6 +225,7 @@ struct at91_adc_trigger {
 	char				*name;
 	unsigned int			trgmod_value;
 	unsigned int			edge_type;
+	bool				hw_trig;
 };
 
 struct at91_adc_state {
@@ -254,16 +255,25 @@ static const struct at91_adc_trigger at91_adc_trigger_list[] = {
 		.name = "external_rising",
 		.trgmod_value = AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_RISE,
 		.edge_type = IRQ_TYPE_EDGE_RISING,
+		.hw_trig = true,
 	},
 	{
 		.name = "external_falling",
 		.trgmod_value = AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_FALL,
 		.edge_type = IRQ_TYPE_EDGE_FALLING,
+		.hw_trig = true,
 	},
 	{
 		.name = "external_any",
 		.trgmod_value = AT91_SAMA5D2_TRGR_TRGMOD_EXT_TRIG_ANY,
 		.edge_type = IRQ_TYPE_EDGE_BOTH,
+		.hw_trig = true,
+	},
+	{
+		.name = "software",
+		.trgmod_value = AT91_SAMA5D2_TRGR_TRGMOD_NO_TRIGGER,
+		.edge_type = IRQ_TYPE_NONE,
+		.hw_trig = false,
 	},
 };
 
@@ -597,7 +607,7 @@ static int at91_adc_probe(struct platform_device *pdev)
 	struct at91_adc_state *st;
 	struct resource	*res;
 	int ret, i;
-	u32 edge_type;
+	u32 edge_type = IRQ_TYPE_NONE;
 
 	indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*st));
 	if (!indio_dev)
@@ -641,14 +651,14 @@ static int at91_adc_probe(struct platform_device *pdev)
 	ret = of_property_read_u32(pdev->dev.of_node,
 				   "atmel,trigger-edge-type", &edge_type);
 	if (ret) {
-		dev_err(&pdev->dev,
-			"invalid or missing value for atmel,trigger-edge-type\n");
-		return ret;
+		dev_dbg(&pdev->dev,
+			"atmel,trigger-edge-type not specified, only software trigger available\n");
 	}
 
 	st->selected_trig = NULL;
 
-	for (i = 0; i < AT91_SAMA5D2_HW_TRIG_CNT; i++)
+	/* find the right trigger, or no trigger at all */
+	for (i = 0; i < AT91_SAMA5D2_HW_TRIG_CNT + 1; i++)
 		if (at91_adc_trigger_list[i].edge_type == edge_type) {
 			st->selected_trig = &at91_adc_trigger_list[i];
 			break;
@@ -717,24 +727,27 @@ static int at91_adc_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, indio_dev);
 
-	ret = at91_adc_buffer_init(indio_dev);
-	if (ret < 0) {
-		dev_err(&pdev->dev, "couldn't initialize the buffer.\n");
-		goto per_clk_disable_unprepare;
-	}
+	if (st->selected_trig->hw_trig) {
+		ret = at91_adc_buffer_init(indio_dev);
+		if (ret < 0) {
+			dev_err(&pdev->dev, "couldn't initialize the buffer.\n");
+			goto per_clk_disable_unprepare;
+		}
 
-	ret = at91_adc_trigger_init(indio_dev);
-	if (ret < 0) {
-		dev_err(&pdev->dev, "couldn't setup the triggers.\n");
-		goto per_clk_disable_unprepare;
+		ret = at91_adc_trigger_init(indio_dev);
+		if (ret < 0) {
+			dev_err(&pdev->dev, "couldn't setup the triggers.\n");
+			goto per_clk_disable_unprepare;
+		}
 	}
 
 	ret = iio_device_register(indio_dev);
 	if (ret < 0)
 		goto per_clk_disable_unprepare;
 
-	dev_info(&pdev->dev, "setting up trigger as %s\n",
-		 st->selected_trig->name);
+	if (st->selected_trig->hw_trig)
+		dev_info(&pdev->dev, "setting up trigger as %s\n",
+			 st->selected_trig->name);
 
 	dev_info(&pdev->dev, "version: %x\n",
 		 readl_relaxed(st->base + AT91_SAMA5D2_VERSION));