From: Derek Keith <derek@codeurge.com>
Date: Mon, 23 Mar 2026 11:11:58 +0000 (-0600)
Subject: USB-Audio: Scarlett 18i20 fix ADAT capture channel count for Gen 1/2
X-Git-Url: https://git.alsa-project.org/?a=commitdiff_plain;h=17b48b1aa77401bbe084cad3dd17dd98ba676ad1;p=alsa-ucm-conf.git

USB-Audio: Scarlett 18i20 fix ADAT capture channel count for Gen 1/2

The Scarlett 18i20 Gen 1 (0x800c) and Gen 2 (0x8201) have 18 capture
channels, but the ADAT Optical Input device ("Direct 2") unconditionally
maps 8 channels (indices 12-19). Channel indices 18 and 19 exceed the
available capture channels, causing WirePlumber/PipeWire to reject the
UCM profile:

  spa.alsa: Error in ALSA UCM profile for _ucm0003.hw:USB,0 (Direct2):
    CaptureChannel6=18 >= CaptureChannels=18

Conditionally size the ADAT capture device based on DirectCaptureChannels:
- Gen 1/2 (18 channels): 6-channel ADAT (indices 12-17)
- Gen 3+ (20+ channels): 8-channel ADAT (indices 12-19)

Tested on a Scarlett 18i20 Gen 2 (USB1235:8201) running PipeWire 1.4
with WirePlumber on CachyOS.

Closes: https://github.com/alsa-project/alsa-ucm-conf/pull/731
Signed-off-by: Derek Keith <derek@codeurge.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
---

diff --git a/ucm2/USB-Audio/Focusrite/Scarlett-18i20-HiFi.conf b/ucm2/USB-Audio/Focusrite/Scarlett-18i20-HiFi.conf
index 4ad0af1..aced27b 100644
--- a/ucm2/USB-Audio/Focusrite/Scarlett-18i20-HiFi.conf
+++ b/ucm2/USB-Audio/Focusrite/Scarlett-18i20-HiFi.conf
@@ -519,34 +519,71 @@ SectionDevice."SPDIF 3" {
 }
 
 # Digital (Professional) Inputs
+#
+# Gen 1/2 have 18 capture channels (ADAT 1-6), Gen 3+ have 20 (ADAT 1-8).
+# Channel indices 18-19 are out of bounds when DirectCaptureChannels is 18,
+# so conditionally size the ADAT capture device.
+
+If.adat_in_18ch {
+	Condition {
+		Type String
+		String1 "${var:DirectCaptureChannels}"
+		String2 "18"
+	}
+	True.SectionDevice."Direct 2" {
+		Comment "ADAT Optical Input"
+
+		Value {
+			CapturePriority 48
+		}
 
-SectionDevice."Direct 2" {
-	Comment "ADAT Optical Input"
-
-	Value {
-		CapturePriority 48
+		Macro.pcm_split.SplitPCMDevice {
+			Name "18i20_adat_in"
+			Direction Capture
+			HWChannels "${var:DirectCaptureChannels}"
+			Channels 6
+			Channel0 12
+			Channel1 13
+			Channel2 14
+			Channel3 15
+			Channel4 16
+			Channel5 17
+			ChannelPos0 UNKNOWN
+			ChannelPos1 UNKNOWN
+			ChannelPos2 UNKNOWN
+			ChannelPos3 UNKNOWN
+			ChannelPos4 UNKNOWN
+			ChannelPos5 UNKNOWN
+		}
 	}
+	False.SectionDevice."Direct 2" {
+		Comment "ADAT Optical Input"
 
-	Macro.pcm_split.SplitPCMDevice {
-		Name "18i20_adat_in"
-		Direction Capture
-		HWChannels "${var:DirectCaptureChannels}"
-		Channels 8
-		Channel0 12
-		Channel1 13
-		Channel2 14
-		Channel3 15
-		Channel4 16
-		Channel5 17
-		Channel6 18
-		Channel7 19
-		ChannelPos0 UNKNOWN
-		ChannelPos1 UNKNOWN
-		ChannelPos2 UNKNOWN
-		ChannelPos3 UNKNOWN
-		ChannelPos4 UNKNOWN
-		ChannelPos5 UNKNOWN
-		ChannelPos6 UNKNOWN
-		ChannelPos7 UNKNOWN
+		Value {
+			CapturePriority 48
+		}
+
+		Macro.pcm_split.SplitPCMDevice {
+			Name "18i20_adat_in"
+			Direction Capture
+			HWChannels "${var:DirectCaptureChannels}"
+			Channels 8
+			Channel0 12
+			Channel1 13
+			Channel2 14
+			Channel3 15
+			Channel4 16
+			Channel5 17
+			Channel6 18
+			Channel7 19
+			ChannelPos0 UNKNOWN
+			ChannelPos1 UNKNOWN
+			ChannelPos2 UNKNOWN
+			ChannelPos3 UNKNOWN
+			ChannelPos4 UNKNOWN
+			ChannelPos5 UNKNOWN
+			ChannelPos6 UNKNOWN
+			ChannelPos7 UNKNOWN
+		}
 	}
 }