diff --git a/core/internal/server/brightness/ddc.go b/core/internal/server/brightness/ddc.go
index e362f2b05..9ce1dce0f 100644
--- a/core/internal/server/brightness/ddc.go
+++ b/core/internal/server/brightness/ddc.go
@@ -24,7 +24,6 @@ const (
 	EDID_ADDR       = 0x50
 )
 
-// ddcutil's DEFAULT_FLOCK_POLL_MILLISEC and DEFAULT_FLOCK_MAX_WAIT_MILLISEC (src/base/parms.h).
 const (
 	ddcBusLockPoll = 100 * time.Millisecond
 	ddcBusLockWait = 3 * time.Second
@@ -178,8 +177,7 @@ func (b *DDCBackend) probeDDCDevice(bus int, readEDID bool) (*ddcDevice, error)
 	return dev, nil
 }
 
-// Based on ddcutil's i2c_open_bus() cross-instance lock (src/base/flock.c): ddcutil, other dms
-// processes and this one take turns on a bus.
+// flock on the device node is how ddc tools and other dms processes take turns on a bus.
 func openDDCBus(bus int) (int, error) {
 	// Without O_CLOEXEC a process spawned mid-probe inherits the fd and the flock with it.
 	fd, err := syscall.Open(fmt.Sprintf("/dev/i2c-%d", bus), syscall.O_RDWR|syscall.O_CLOEXEC, 0)
@@ -207,7 +205,6 @@ func setI2CAddr(fd, addr int) error {
 	return nil
 }
 
-// Based on ddcutil's i2c_detect_x37() (src/i2c/i2c_x37.c).
 func detectX37(fd int) bool {
 	if n, err := syscall.Read(fd, make([]byte, 1)); err == nil && n == 1 {
 		return true
@@ -216,7 +213,6 @@ func detectX37(fd int) bool {
 	return err == nil
 }
 
-// Based on ddcutil's i2c_get_raw_edid_by_fd() with the fileio reader (src/i2c/i2c_edid.c).
 func readBusEDID(fd int) ([]byte, error) {
 	if err := setI2CAddr(fd, EDID_ADDR); err != nil {
 		return nil, err
@@ -507,8 +503,7 @@ func (b *DDCBackend) setBrightnessImmediateWithExponent(id string, value int) er
 	return nil
 }
 
-// Based on ddcutil's i2c_check_open_bus_alive() (src/i2c/i2c_bus_core.c), sysfs side only. Known
-// devices are keyed by bus number, which the kernel hands to the next adapter once one goes away.
+// Known devices are keyed by bus number, which the kernel hands to the next adapter once one goes away.
 func (b *DDCBackend) checkBusAlive(dev *ddcDevice) error {
 	if isIgnorableI2CBus(dev.bus) || getI2CDeviceSysfsName(dev.bus) != dev.adapter {
 		return errBusReused
diff --git a/core/internal/server/brightness/ddc_filter.go b/core/internal/server/brightness/ddc_filter.go
index 519e8e5ac..68fb834ee 100644
--- a/core/internal/server/brightness/ddc_filter.go
+++ b/core/internal/server/brightness/ddc_filter.go
@@ -13,8 +13,6 @@ import (
 	"github.com/AvengeMedia/DankMaterialShell/core/internal/log"
 )
 
-// isIgnorableI2CBus checks if an I2C bus should be skipped during DDC probing.
-// Based on ddcutil's sysfs_is_ignorable_i2c_device() (src/sysfs/sysfs_simple.c)
 func isIgnorableI2CBus(busno int) bool {
 	name := getI2CDeviceSysfsName(busno)
 	if name == "DPMST" {
@@ -42,7 +40,6 @@ func isIgnorableI2CBus(busno int) bool {
 	return ignorable
 }
 
-// Based on ddcutil's ignorable_i2c_device_sysfs_name() (src/sysfs/sysfs_simple.c)
 func isIgnorableI2CDeviceName(name, driver string) bool {
 	ignorablePrefixes := []string{
 		"SMBus",
@@ -69,7 +66,6 @@ func isIgnorableI2CDeviceName(name, driver string) bool {
 	return false
 }
 
-// Based on ddcutil's get_i2c_device_sysfs_name() (sysfs_base.c:1175)
 func getI2CDeviceSysfsName(busno int) string {
 	path := fmt.Sprintf("/sys/bus/i2c/devices/i2c-%d/name", busno)
 	data, err := os.ReadFile(path)
@@ -79,7 +75,6 @@ func getI2CDeviceSysfsName(busno int) string {
 	return strings.TrimSpace(string(data))
 }
 
-// Based on ddcutil's get_i2c_device_sysfs_class() (src/sysfs/sysfs_simple.c)
 func getI2CDeviceSysfsClass(busno int) uint32 {
 	paths := []string{
 		fmt.Sprintf("/sys/bus/i2c/devices/i2c-%d", busno),
@@ -103,7 +98,6 @@ func getI2CDeviceSysfsClass(busno int) uint32 {
 	return 0
 }
 
-// Based on ddcutil's get_driver_for_busno() (src/sysfs/sysfs_simple.c)
 func getI2CSysfsDriver(busno int) string {
 	adapter := findI2CAdapter(fmt.Sprintf("/sys/bus/i2c/devices/i2c-%d", busno))
 	if adapter == "" {
@@ -116,8 +110,7 @@ func getI2CSysfsDriver(busno int) string {
 	return filepath.Base(module)
 }
 
-// Based on ddcutil's sysfs_find_adapter() (src/sysfs/sysfs_simple.c): the nearest
-// ancestor under /sys/devices carrying a class attribute.
+// The nearest ancestor under /sys/devices carrying a class attribute.
 func findI2CAdapter(path string) string {
 	resolved, err := filepath.EvalSymlinks(path)
 	if err != nil {
@@ -132,8 +125,7 @@ func findI2CAdapter(path string) string {
 	return ""
 }
 
-// ddcutil's known_reliable_drivers (src/sysfs/sysfs_base.c): drivers that keep the DRM connector
-// edid, status and dpms attributes current.
+// Drivers that keep the DRM connector edid, status and dpms attributes current; nvidia does not.
 var sysfsReliableDrivers = []string{"i915", "xe", "amdgpu", "radeon", "nouveau"}
 
 var (
@@ -149,7 +141,6 @@ const (
 	ddcBusNeedsEDIDRead
 )
 
-// Based on ddcutil's i2c_edid_exists() and its laptop panel exclusion (src/i2c/i2c_bus_core.c).
 func ddcBusVerdictFor(busno int, connectors map[int]string) ddcBusVerdict {
 	name := getI2CDeviceSysfsName(busno)
 	displayLink := name == "DisplayLink I2C Adapter"
@@ -177,7 +168,6 @@ func ddcBusVerdictFor(busno int, connectors map[int]string) ddcBusVerdict {
 	return ddcBusNeedsEDIDRead
 }
 
-// Based on ddcutil's dpms_check_drm_asleep_by_businfo() (src/sysfs/sysfs_dpms.c).
 func ddcDisplayAsleep(busno int, connectors map[int]string) bool {
 	connector, mapped := connectors[busno]
 	if !mapped || !slices.Contains(sysfsReliableDrivers, getI2CSysfsDriver(busno)) {
@@ -186,11 +176,13 @@ func ddcDisplayAsleep(busno int, connectors map[int]string) bool {
 	return strings.TrimSpace(drmConnectorAttr(connector, "dpms")) != "On"
 }
 
-// Based on ddcutil's get_connector_bus_numbers() (src/sysfs/sysfs_simple.c): a DP connector's own
-// i2c-N directory, any other connector's ddc/i2c-dev/i2c-N.
 func drmConnectorsByBus() map[int]string {
+	return drmConnectorsByBusIn("/sys/class/drm")
+}
+
+func drmConnectorsByBusIn(root string) map[int]string {
 	connectors := map[int]string{}
-	entries, err := os.ReadDir("/sys/class/drm")
+	entries, err := os.ReadDir(root)
 	if err != nil {
 		return connectors
 	}
@@ -199,17 +191,29 @@ func drmConnectorsByBus() map[int]string {
 		if !drmConnectorPattern.MatchString(name) {
 			continue
 		}
-		dir := filepath.Join("/sys/class/drm", name)
-		if !strings.Contains(name, "-DP-") {
-			dir = filepath.Join(dir, "ddc", "i2c-dev")
-		}
-		if busno, ok := i2cSubdirBus(dir); ok {
+		for _, busno := range drmConnectorBuses(name, filepath.Join(root, name)) {
 			connectors[busno] = name
 		}
 	}
 	return connectors
 }
 
+// amdgpu gives a DP connector two buses, the aux channel under i2c-N and the hardware i2c bus
+// behind ddc, and a DP++ to HDMI adapter answers only on the ddc one (#3724).
+func drmConnectorBuses(name, dir string) []int {
+	buses := []int{}
+	if busno, ok := i2cSubdirBus(filepath.Join(dir, "ddc", "i2c-dev")); ok {
+		buses = append(buses, busno)
+	}
+	if !strings.Contains(name, "-DP-") {
+		return buses
+	}
+	if busno, ok := i2cSubdirBus(dir); ok {
+		buses = append(buses, busno)
+	}
+	return buses
+}
+
 func i2cSubdirBus(dir string) (int, bool) {
 	entries, err := os.ReadDir(dir)
 	if err != nil {
@@ -237,7 +241,6 @@ func drmConnectorAttr(connector, attr string) string {
 
 var edidHeader = []byte{0x00, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00}
 
-// Based on ddcutil's is_valid_raw_edid() (src/util/edid.c).
 func isValidEDID(edid []byte) bool {
 	if len(edid) < 128 || !bytes.Equal(edid[:8], edidHeader) {
 		return false
@@ -249,12 +252,11 @@ func isValidEDID(edid []byte) bool {
 	return sum == 0
 }
 
-// Based on ddcutil's is_laptop_parsed_edid() (src/util/edid.c).
+// A panel with neither a monitor name nor a serial descriptor is a laptop panel.
 func isLaptopEDID(edid []byte) bool {
 	return edidDescriptorText(edid, 0xfc) == "" && edidDescriptorText(edid, 0xff) == ""
 }
 
-// Based on ddcutil's get_edid_descriptor_strings() (src/util/edid.c).
 func edidDescriptorText(edid []byte, tag byte) string {
 	text := ""
 	for i := range 4 {
diff --git a/core/internal/server/brightness/ddc_filter_test.go b/core/internal/server/brightness/ddc_filter_test.go
index e05f02c42..79ff37399 100644
--- a/core/internal/server/brightness/ddc_filter_test.go
+++ b/core/internal/server/brightness/ddc_filter_test.go
@@ -1,6 +1,9 @@
 package brightness
 
 import (
+	"maps"
+	"os"
+	"path/filepath"
 	"testing"
 )
 
@@ -71,3 +74,25 @@ func TestIsIgnorableI2CDeviceName(t *testing.T) {
 		})
 	}
 }
+
+func TestDrmConnectorsByBusMapsBothDPBuses(t *testing.T) {
+	root := t.TempDir()
+	for _, dir := range []string{
+		"card1-DP-2/i2c-13",
+		"card1-DP-2/ddc/i2c-dev/i2c-4",
+		"card1-HDMI-A-1/ddc/i2c-dev/i2c-2",
+		"card1-DP-9",
+		"renderD128",
+	} {
+		if err := os.MkdirAll(filepath.Join(root, dir), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	got := drmConnectorsByBusIn(root)
+
+	want := map[int]string{13: "card1-DP-2", 4: "card1-DP-2", 2: "card1-HDMI-A-1"}
+	if !maps.Equal(got, want) {
+		t.Fatalf("drmConnectorsByBusIn() = %v, want %v", got, want)
+	}
+}