mfd: stm32-timers: Use dma_request_chan() instead dma_request_slave_channel()

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

By using dma_request_chan() directly the driver can support deferred
probing against DMA.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/stm32-timers.c

@@ -167,10 +167,11 @@ static void stm32_timers_get_arr_size(struct stm32_timers *ddata)
 	regmap_write(ddata->regmap, TIM_ARR, 0x0);
 }
 
-static void stm32_timers_dma_probe(struct device *dev,
+static int stm32_timers_dma_probe(struct device *dev,
 				   struct stm32_timers *ddata)
 {
 	int i;
+	int ret = 0;
 	char name[4];
 
 	init_completion(&ddata->dma.completion);
@@ -179,14 +180,23 @@ static void stm32_timers_dma_probe(struct device *dev,
 	/* Optional DMA support: get valid DMA channel(s) or NULL */
 	for (i = STM32_TIMERS_DMA_CH1; i <= STM32_TIMERS_DMA_CH4; i++) {
 		snprintf(name, ARRAY_SIZE(name), "ch%1d", i + 1);
-		ddata->dma.chans[i] = dma_request_slave_channel(dev, name);
+		ddata->dma.chans[i] = dma_request_chan(dev, name);
 	}
-	ddata->dma.chans[STM32_TIMERS_DMA_UP] =
-		dma_request_slave_channel(dev, "up");
-	ddata->dma.chans[STM32_TIMERS_DMA_TRIG] =
-		dma_request_slave_channel(dev, "trig");
-	ddata->dma.chans[STM32_TIMERS_DMA_COM] =
-		dma_request_slave_channel(dev, "com");
+	ddata->dma.chans[STM32_TIMERS_DMA_UP] = dma_request_chan(dev, "up");
+	ddata->dma.chans[STM32_TIMERS_DMA_TRIG] = dma_request_chan(dev, "trig");
+	ddata->dma.chans[STM32_TIMERS_DMA_COM] = dma_request_chan(dev, "com");
+
+	for (i = STM32_TIMERS_DMA_CH1; i < STM32_TIMERS_MAX_DMAS; i++) {
+		if (IS_ERR(ddata->dma.chans[i])) {
+			/* Save the first error code to return */
+			if (PTR_ERR(ddata->dma.chans[i]) != -ENODEV && !ret)
+				ret = PTR_ERR(ddata->dma.chans[i]);
+
+			ddata->dma.chans[i] = NULL;
+		}
+	}
+
+	return ret;
 }
 
 static void stm32_timers_dma_remove(struct device *dev,
@@ -230,7 +240,11 @@ static int stm32_timers_probe(struct platform_device *pdev)
 
 	stm32_timers_get_arr_size(ddata);
 
-	stm32_timers_dma_probe(dev, ddata);
+	ret = stm32_timers_dma_probe(dev, ddata);
+	if (ret) {
+		stm32_timers_dma_remove(dev, ddata);
+		return ret;
+	}
 
 	platform_set_drvdata(pdev, ddata);