[nrf fromtree] tests: drivers: spi: spi_loopback: configure spi latency expectation

Allow to customize scaling factor used to compare ideal spi transfer
and measured one.

Signed-off-by: Piotr Kosycarz <[email protected]>
(cherry picked from commit d700619)

Author: nordic-piks

tests/drivers/spi/spi_loopback/Kconfig

@@ -11,6 +11,10 @@ config SPI_LARGE_BUFFER_SIZE
 	int "Large buffer size"
 	default 8192
 
+config SPI_IDEAL_TRANSFER_DURATION_SCALING
+	int "Scaling factor to compare ideal and measured SPI transfer duration"
+	default 8
+
 if SOC_SERIES_STM32H7X
 
 config SPI_LOOPBACK_16BITS_FRAMES

tests/drivers/spi/spi_loopback/boards/nrf54h20dk_nrf54h20_cpuapp.conf

@@ -0,0 +1 @@
+CONFIG_SPI_IDEAL_TRANSFER_DURATION_SCALING=12

tests/drivers/spi/spi_loopback/boards/nrf54h20dk_nrf54h20_cpurad.conf

@@ -0,0 +1 @@
+CONFIG_SPI_IDEAL_TRANSFER_DURATION_SCALING=12

tests/drivers/spi/spi_loopback/src/spi.c

@@ -327,7 +327,7 @@ ZTEST(spi_loopback, test_spi_complete_multiple_timed)
 
 	/* Fail if transfer is faster than theoretically possible */
 	zassert_true(time_spent_us >= minimum_transfer_time_us,
-			"Transfer faster than theoretically possible");
+		     "Transfer faster than theoretically possible");
 
 	/* handle overflow for print statement */
 	latency_measurement = time_spent_us - expected_transfer_time_us;
@@ -337,7 +337,9 @@ ZTEST(spi_loopback, test_spi_complete_multiple_timed)
 	TC_PRINT("Latency measurement: %llu us\n", latency_measurement);
 
 	/* Allow some overhead, but not too much */
-	zassert_true(time_spent_us <= expected_transfer_time_us * 8, "Very high latency");
+	zassert_true(time_spent_us <=
+			     expected_transfer_time_us * CONFIG_SPI_IDEAL_TRANSFER_DURATION_SCALING,
+		     "Very high latency");
 
 	spi_loopback_compare_bufs(buffer_tx, buffer_rx, BUF_SIZE,
 				  buffer_print_tx, buffer_print_rx);