[PATCH v4 07/11] ALSA: oxfw: add comment for the type of ASICs

[Takashi Sakamoto <o-takashi@sakamocchi.jp>]

ALSA OXFW supports two types of ASICS; OXFW970 and OXFW971. The former
is known to have a quirk we call 'jumbo payload' that some isochronous
cycles are skipped to transfer isochronous packets during handling
asynchronous transaction. The quirk seems to correspond to firmware
initially delivered by Oxford Semiconductor since the quirk is not
confirmed for Mackie Onyx Satellite in which the revised firmware is
available. The quirk is not confirmed in the latter.

This commit adds code comment to describe the quirk.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
---
 sound/firewire/oxfw/oxfw.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/sound/firewire/oxfw/oxfw.c b/sound/firewire/oxfw/oxfw.c
index e851149c5280..9a9c84bc811a 100644
--- a/sound/firewire/oxfw/oxfw.c
+++ b/sound/firewire/oxfw/oxfw.c
@@ -332,14 +332,30 @@ static const struct compat_info lacie_speakers = {
 }
 
 static const struct ieee1394_device_id oxfw_id_table[] = {
+	//
+	// OXFW970 devices:
+	// Initial firmware has a quirk to postpone isoc packet transmission during finishing async
+	// transaction. As a result, several isochronous cycles are skipped to transfer the packets
+	// and the audio data frames which should have been transferred during the cycles are put
+	// into packet at the first isoc cycle after the postpone. Furthermore, the value of SYT
+	// field in CIP header is not reliable as synchronization timing,
+	//
 	OXFW_DEV_ENTRY(VENDOR_GRIFFIN, 0x00f970, &griffin_firewave),
 	OXFW_DEV_ENTRY(VENDOR_LACIE, 0x00f970, &lacie_speakers),
-	// Behringer,F-Control Audio 202.
+	// Behringer,F-Control Audio 202. The value of SYT field is not reliable at all.
 	OXFW_DEV_ENTRY(VENDOR_BEHRINGER, 0x00fc22, NULL),
-	// Loud Technologies, Tapco Link.FireWire 4x6.
+	// Loud Technologies, Tapco Link.FireWire 4x6. The value of SYT field is always 0xffff.
 	OXFW_DEV_ENTRY(VENDOR_LOUD, 0x000460, NULL),
-	// Loud Technologies, Mackie Onyx Satellite.
+	// Loud Technologies, Mackie Onyx Satellite. Although revised version of firmware is
+	// installed to avoid the postpone, the value of SYT field is always 0xffff.
 	OXFW_DEV_ENTRY(VENDOR_LOUD, MODEL_SATELLITE, NULL),
+	// Miglia HarmonyAudio. Not yet identified.
+
+	//
+	// OXFW971 devices:
+	// The value of SYT field in CIP header is enough reliable. Both of blocking and non-blocking
+	// transmission methods are available.
+	//
 	// Any Mackie(Loud) models (name string/model id):
 	//  Onyx-i series (former models):	0x081216
 	//  Onyx 1640i:				0x001640
-- 
2.27.0