[nrf fromlist] tests: drivers: i2s: i2s_speed: Confirm CLK value

Add test which confirms correct clock divider selection.

Frame rate selected by the user may not be obtained due to
PCLK clock value and finite number of clock divider value.
In such case, driver shall select divider that results in
frame clock rate closest to the requested value.
There was a bug that was discarding perfect match divider.

Upstream PR #: TBD

Signed-off-by: Sebastian Głąb <[email protected]>

Author: nordic-segl

tests/drivers/i2s/i2s_speed/testcase.yaml

@@ -29,3 +29,33 @@ tests:
       fixture: gpio_loopback
     extra_args: EXTRA_DTC_OVERLAY_FILE="boards/nrf5340dk_nrf5340_cpuapp_aclk.overlay"
     platform_allow: nrf5340dk/nrf5340/cpuapp
+  drivers.i2s.speed.gpio_loopback.clk_divider:
+    tags:
+      - drivers
+      - i2s
+    platform_allow:
+      - nrf52840dk/nrf52840
+      - nrf5340dk/nrf5340/cpuapp
+      - nrf54l15dk/nrf54l15/cpuapp
+    extra_args:
+      - CONFIG_I2S_LOG_LEVEL_INF=y
+    harness: console
+    harness_config:
+      fixture: gpio_loopback
+      type: multi_line
+      ordered: true
+      regex:
+        - "transfer_short_08000"
+        - "I2S MCK frequency: 256000, actual PCM rate: 8000"
+        - "transfer_short_16000"
+        - "I2S MCK frequency: 507936, actual PCM rate: 15873"
+        - "transfer_short_32000"
+        - "I2S MCK frequency: 1032258, actual PCM rate: 32258"
+        - "transfer_short_44100"
+        - "I2S MCK frequency: 1391304, actual PCM rate: 43478"
+        - "transfer_short_48000"
+        - "I2S MCK frequency: 1523809, actual PCM rate: 47619"
+        - "transfer_short_88200"
+        - "I2S MCK frequency: 2909090, actual PCM rate: 90909"
+        - "transfer_short_96000"
+        - "I2S MCK frequency: 3200000, actual PCM rate: 100000"