tests: drivers: lpuart: Fix two chip test

Test which run on nrf9160 and nrf52480 was failing as uart driver
is now releasing UART pins when in idle. It means that TX pin should
have pull-up as otherwise it is floating and can lead to errors in
the communication. Test was failing due to that.

Added pull-ups to TX pins in pinctrl sleep state.
Enforced pinctrl sleep state to be present (event when PM device
is not used).
Added detection of premature test completion which could lead to
false positive. Test is now failing if too few packets are received.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

Author: nordic-krch

tests/drivers/lpuart/boards/nrf9160dk_nrf52840.overlay

@@ -18,8 +18,13 @@
 
 	uart1_sleep_alt: uart1_sleep_alt {
 		group1 {
-			psels = <NRF_PSEL(UART_TX, 0, 17)>,
-				<NRF_PSEL(UART_RX, 0, 20)>;
+			psels = <NRF_PSEL(UART_TX, 0, 17)>;
+			low-power-enable;
+			bias-pull-up;
+		};
+
+		group2 {
+			psels = <NRF_PSEL(UART_RX, 0, 20)>;
 			low-power-enable;
 		};
 	};

tests/drivers/lpuart/boards/nrf9160dk_nrf9160.overlay

@@ -34,8 +34,13 @@
 
 	uart2_sleep_alt: uart2_sleep_alt {
 		group1 {
-			psels = <NRF_PSEL(UART_RX, 0, 17)>,
-				<NRF_PSEL(UART_TX, 0, 18)>;
+			psels = <NRF_PSEL(UART_TX, 0, 18)>;
+			low-power-enable;
+			bias-pull-up;
+		};
+
+		group2 {
+			psels = <NRF_PSEL(UART_RX, 0, 17)>;
 			low-power-enable;
 		};
 	};

tests/drivers/lpuart/prj.conf

@@ -13,5 +13,6 @@ CONFIG_TEST_LOGGING_DEFAULTS=n
 CONFIG_COUNTER=y
 
 CONFIG_TEST_LPUART_TIMEOUT=10
+CONFIG_PINCTRL_KEEP_SLEEP_STATE=y
 
 CONFIG_ASSERT=y

tests/drivers/lpuart/src/main.c

@@ -238,6 +238,8 @@ ZTEST(test_lpuart_stress, test_stress)
 	k_timer_stop(&kill_timer);
 	zassert_equal(err, 0, NULL);
 	zassert_false(test_err, NULL);
+	/* Detect premature kill packet. */
+	zassert_true(rx_cnt > 100);
 	zassert_equal(tx_req_cnt, tx_done_cnt, NULL);
 
 	k_msleep(100);