settings: get and use current host number for K375sFnSwap because of bug in firmware of MX Keys S

lib/logitech_receiver/settings_templates.py

@@ -231,12 +231,25 @@ _descriptors.get_usbid(0xC066).settings = [_PerformanceMXDpi, RegisterSmoothScro
 
 
 # ignore the capabilities part of the feature - all devices should be able to swap Fn state
-# just use the current host (first byte = 0xFF) part of the feature to read and set the Fn state
+# can't just use the first byte = 0xFF (for current host) because of a bug in the firmware of the MX Keys S
 class K375sFnSwap(FnSwapVirtual):
     feature = _F.K375S_FN_INVERSION
-    rw_options = {"prefix": b"\xFF"}
     validator_options = {"true_value": b"\x01", "false_value": b"\x00", "read_skip_byte_count": 1}
 
+    class rw_class(_FeatureRW):
+        def find_current_host(self, device):
+            if not self.prefix:
+                response = device.feature_request(_F.HOSTS_INFO, 0x00)
+                self.prefix = response[3:4] if response else b"\xFF"
+
+        def read(self, device, data_bytes=b""):
+            self.find_current_host(device)
+            return super().read(device, data_bytes)
+
+        def write(self, device, data_bytes):
+            self.find_current_host(device)
+            return super().write(device, data_bytes)
+
 
 class FnSwap(FnSwapVirtual):
     feature = _F.FN_INVERSION

tests/logitech_receiver/test_setting_templates.py

@@ -119,6 +119,19 @@ simple_tests = [
         hidpp.Response("FF0001", 0x0600, "FF"),
         hidpp.Response("FF0101", 0x0610, "FF01"),
     ),
+    Setup(
+        FeatureTest(settings_templates.K375sFnSwap, False, True, offset=0x06),
+        hidpp.Response("050001", 0x0000, "1815"),  # HOSTS_INFO
+        hidpp.Response("FF0001", 0x0600, "FF"),
+        hidpp.Response("FF0101", 0x0610, "FF01"),
+    ),
+    Setup(
+        FeatureTest(settings_templates.K375sFnSwap, False, True, offset=0x06),
+        hidpp.Response("050001", 0x0000, "1815"),  # HOSTS_INFO
+        hidpp.Response("07050301", 0x0500),  # current host is 0x01, i.e., host 2
+        hidpp.Response("010001", 0x0600, "01"),
+        hidpp.Response("010101", 0x0610, "0101"),
+    ),
     Setup(
         FeatureTest(settings_templates.FnSwap, True, False),
         hidpp.Response("01", 0x0400),
@@ -474,6 +487,7 @@ def mock_gethostname(mocker):
 @pytest.mark.parametrize("test", simple_tests)
 def test_simple_template(test, mocker, mock_gethostname):
     tst = test.test
+    print("TEST", tst.sclass.feature)
     device = hidpp.Device(responses=test.responses, feature=tst.sclass.feature, offset=tst.offset, version=tst.version)
     spy_request = mocker.spy(device, "request")