From a284e438f1952315631f354dee2b30b264afb324 Mon Sep 17 00:00:00 2001
From: Valentin Milea <valentin.milea@gmail.com>
Date: Fri, 7 Jan 2022 15:02:52 +0200
Subject: [PATCH] Disable feedback format correction by default #1234

---
 src/class/audio/audio_device.c |  6 ++----
 src/class/audio/audio_device.h | 22 +++++++++++-----------
 2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/src/class/audio/audio_device.c b/src/class/audio/audio_device.c
index a461e97c52..5ffc9b0dc4 100644
--- a/src/class/audio/audio_device.c
+++ b/src/class/audio/audio_device.c
@@ -2247,14 +2247,12 @@ static void audiod_parse_for_AS_params(audiod_function_t* audio, uint8_t const *
 
 #if CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
 
-// Input value feedback has to be in 16.16 format - the format will be converted according to speed settings automatically
-// unless format correction is disabled.
 bool tud_audio_n_fb_set(uint8_t func_id, uint32_t feedback)
 {
   TU_VERIFY(func_id < CFG_TUD_AUDIO && _audiod_fct[func_id].p_desc != NULL);
 
   // Format the feedback value
-#if !TUD_OPT_HIGH_SPEED && !CFG_TUD_AUDIO_DISABLE_FEEDBACK_FORMAT_CORRECTION
+#if CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION && !TUD_OPT_HIGH_SPEED
   uint8_t * fb = (uint8_t *) &_audiod_fct[func_id].fb_val;
 
   // For FS format is 10.14
@@ -2264,7 +2262,7 @@ bool tud_audio_n_fb_set(uint8_t func_id, uint32_t feedback)
   // 4th byte is needed to work correctly with MS Windows
   *fb = 0;
 #else
-  // For HS format is 16.16 as originally demanded
+  // Send value as-is, caller will choose the appropriate format
   _audiod_fct[func_id].fb_val = feedback;
 #endif
 
diff --git a/src/class/audio/audio_device.h b/src/class/audio/audio_device.h
index 731fd6c018..f406cf2811 100644
--- a/src/class/audio/audio_device.h
+++ b/src/class/audio/audio_device.h
@@ -186,9 +186,9 @@
 #define CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP                    0                             // Feedback - 0 or 1
 #endif
 
-// Disable/enable conversion from 16.16 to 10.14 format on high-speed devices. See tud_audio_n_fb_set().
-#ifndef CFG_TUD_AUDIO_DISABLE_FEEDBACK_FORMAT_CORRECTION
-#define CFG_TUD_AUDIO_DISABLE_FEEDBACK_FORMAT_CORRECTION    0                             // 0 or 1
+// Enable/disable conversion from 16.16 to 10.14 format on full-speed devices. See tud_audio_n_fb_set().
+#ifndef CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION
+#define CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION     0                             // 0 or 1
 #endif
 
 // Audio interrupt control EP size - disabled if 0
@@ -459,15 +459,15 @@ TU_ATTR_WEAK bool tud_audio_rx_done_post_read_cb(uint8_t rhport, uint16_t n_byte
 
 #if CFG_TUD_AUDIO_ENABLE_EP_OUT && CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
 TU_ATTR_WEAK bool tud_audio_fb_done_cb(uint8_t rhport);
-// User code should call this function with feedback value in 16.16 format for FS and HS.
-// Value will be corrected for FS to 10.14 format automatically.
-// (see Universal Serial Bus Specification Revision 2.0 5.12.4.2).
-// Feedback value will be sent at FB endpoint interval till it's changed.
+
+// This function is used to provide data rate feedback from an asynchronous sink. Feedback value will be sent at FB endpoint interval till it's changed.
+//
+// The feedback format is specified to be 16.16 for HS and 10.14 for FS devices (see Universal Serial Bus Specification Revision 2.0 5.12.4.2). By default,
+// the choice of format is left to the caller and feedback argument is sent as-is. If CFG_TUD_AUDIO_ENABLE_FEEDBACK_FORMAT_CORRECTION is set, then tinyusb
+// expects 16.16 format and handles the conversion to 10.14 on FS.
 //
-// Note that the USB Audio 2.0 driver on Windows 10 is not following the spec and expects 16.16
-// format for FS. You can define CFG_TUD_AUDIO_DISABLE_FEEDBACK_FORMAT_CORRECTION=1 as a workaround
-// to transmit the feedback value unchanged. Be aware that this might break feedback on other hosts,
-// though at least on Linux the ALSA driver will happily accept either format.
+// Note that due to a bug in its USB Audio 2.0 driver, Windows currently requires 16.16 format for _all_ USB 2.0 devices. On Linux and macOS it seems the 
+// driver can work with either format. So a good compromise is to keep format correction disabled and stick to 16.16 format.
 bool tud_audio_n_fb_set(uint8_t func_id, uint32_t feedback);
 static inline bool tud_audio_fb_set(uint32_t feedback);
 #endif