tests: dma: fix loopback suspend and resume issue

update dma loop test to resolve call sequence issue,
and avoid randum failure due to
dma finished fast than the dma status check. which cause suspend fails.

fixing zephyrproject-rtos#43739

Signed-off-by: Hake Huang <hake.huang@oss.nxp.com>

Author: hakehuang

tests/drivers/dma/loop_transfer/src/test_dma_loop.c

@@ -51,9 +51,12 @@ static __aligned(16) char rx_data[TRANSFER_LOOPS][RX_BUFF_SIZE] = { { 0 } };
 volatile uint8_t transfer_count;
 static struct dma_config dma_cfg = {0};
 static struct dma_block_config dma_block_cfg = {0};
+static int test_case_id;
 
 static void test_transfer(const struct device *dev, uint32_t id)
 {
+	int res = 0;
+
 	transfer_count++;
 	if (transfer_count < TRANSFER_LOOPS) {
 		dma_block_cfg.block_size = strlen(tx_data);
@@ -66,6 +69,16 @@ static void test_transfer(const struct device *dev, uint32_t id)
 		zassert_false(dma_start(dev, id),
 					"Not able to start next transfer %d",
 					transfer_count + 1);
+		if (test_case_id == 1) {
+			res = dma_suspend(dev, id);
+			if (res == -ENOSYS) {
+				TC_PRINT("dma suspend not supported\n");
+				dma_stop(dev, id);
+			} else if (res != 0) {
+				TC_PRINT("ERROR: suspend failed, channel %d, result %d\n", id, res);
+			}
+			test_case_id = 2;
+		}
 	}
 }
 
@@ -90,6 +103,7 @@ static int test_loop(void)
 	const struct device *dma;
 	static int chan_id;
 
+	test_case_id = 0;
 	TC_PRINT("DMA memory to memory transfer started on %s\n",
 	       DMA_DEVICE_NAME);
 	TC_PRINT("Preparing DMA Controller\n");
@@ -176,6 +190,7 @@ static int test_loop_suspend_resume(void)
 	static int chan_id;
 	int res = 0;
 
+	test_case_id = 1;
 	TC_PRINT("DMA memory to memory transfer started on %s\n",
 	       DMA_DEVICE_NAME);
 	TC_PRINT("Preparing DMA Controller\n");
@@ -235,17 +250,6 @@ static int test_loop_suspend_resume(void)
 	while (transfer_count == 0) {
 	}
 
-	res = dma_suspend(dma, chan_id);
-	TC_PRINT("Suspended transfers\n");
-	if (res == -ENOSYS) {
-		TC_PRINT("dma suspend not supported\n");
-		dma_stop(dma, chan_id);
-		return TC_PASS;
-	} else if (res != 0) {
-		TC_PRINT("ERROR: suspend failed, channel %d, result %d\n", chan_id, res);
-		return TC_FAIL;
-	}
-
 	TC_PRINT("Sleeping while suspended\n");
 	k_sleep(K_MSEC(SLEEPTIME));