[PATCH v2] Pioneer devices: engage implicit feedback sync for playback

[Takashi Iwai]

On Fri, 09 Apr 2021 13:07:45 +0200,
Olivia Mackintosh wrote:
> 
> On Mon, Apr 05, 2021 at 10:49:20AM -0300, Geraldo wrote:
> > Dear Linux users of Pioneer gear, please disregard v1 of this patch and
> > test this instead if at all possible.
> > 
> > My initial assessment that we needed to let the capture EP be opened twice
> > was clearly proven wrong by further testing. This is good because if we
> > really needed that it would require a lot of reengineering inside ALSA.
> > 
> > One thing that still boggles my mind though is why we need a special
> > Pioneer case inside snd_usb_parse_implicit_fb_quirk that returns 1 like a
> > capture quirk was found.
> > 
> > This is a highly experimental patch on top of 5.12-rc6 that's supposed to
> > engage implicit feedback sync on the playback for Pioneer devices. Without
> > implicit feedback sync the inputs started glitching due to clock drift in
> > about an hour in my Pioneer DJ DDJ-SR2.
> > 
> > Once again I'd like to thank Takashi Iwai. He's the true author of the bulk
> > of this code, I just adapted it and coerced it into working.
> > 
> > Signed-off-by: Geraldo Nascimento <geraldogabriel at gmail.com>
> 
> Thank you Geraldo and Takashi for working on this patch. I'm currently
> in the process of testing with the DJM-750 but it currently does not
> work as expected. I'll debug futher and report back but would like to
> make you aware of this in the meantime. It may not be a a fundamental
> issue with the patch, but rather something incidental.

Which kernel version have you tested?  There have been quite a few
development about USB-audio recently, so something might be missing or
conflicting?  Let's see.

FWIW, below is a proper patch that is applied on top of for-next
branch of sound.git tree (destined for 5.13 kernel merge).


Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: usb-audio: Re-apply implicit feedback mode to Pioneer
 devices

Pioneer devices are supposed to be working with the implicit feedback
mode, but so far the attempt to applying this caused issues, hence we
explicitly skipped the implicit feedback mode for them.  Recently,
Geraldo discovered that the device actually works if you skip the
generic matching of the sync EPs for the capture stream.  That is, we
should apply the implicit feedback setup for the playback like other
similar devices, while we need to return 1 from
audioformat_capture_quirk() so that no further matching will be done.

This patch implement the application of the implicit feedback to
Pioneer devices.  The former skip_pioneer_sync_ep() was dropped, and
instead we provide is_pioneer_implicit_fb() to check the Pioneer
devices that need the implicit feedback.  In the
audioformat_implicit_fb_quirk(), simply apply the implicit fb for
playback if matching, and in audioformat_capture_quirk()(), it returns
1 if matching, as mentioned in the above.

Reported-by: Geraldo <geraldogabriel at gmail.com>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/implicit.c | 42 ++++++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/sound/usb/implicit.c b/sound/usb/implicit.c
index 4bd9c105a529..427ed0ff3b7b 100644
--- a/sound/usb/implicit.c
+++ b/sound/usb/implicit.c
@@ -171,18 +171,27 @@ static int add_roland_implicit_fb(struct snd_usb_audio *chip,
 				       ifnum, alts);
 }
 
-/* Playback and capture EPs on Pioneer devices share the same iface/altset,
- * but they don't seem working with the implicit fb mode well, hence we
- * just return as if the sync were already set up.
+/* Playback and capture EPs on Pioneer devices share the same iface/altset
+ * for the implicit feedback operation
  */
-static int skip_pioneer_sync_ep(struct snd_usb_audio *chip,
-				struct audioformat *fmt,
-				struct usb_host_interface *alts)
+static bool is_pioneer_implicit_fb(struct snd_usb_audio *chip,
+				   struct usb_host_interface *alts)
+
 {
 	struct usb_endpoint_descriptor *epd;
 
+	if (USB_ID_VENDOR(chip->usb_id) != 0x2b73 &&
+	    USB_ID_VENDOR(chip->usb_id) != 0x08e4)
+		return false;
+	if (alts->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC)
+		return false;
 	if (alts->desc.bNumEndpoints != 2)
-		return 0;
+		return false;
+
+	epd = get_endpoint(alts, 0);
+	if (!usb_endpoint_is_isoc_out(epd) ||
+	    (epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
+		return false;
 
 	epd = get_endpoint(alts, 1);
 	if (!usb_endpoint_is_isoc_in(epd) ||
@@ -191,8 +200,9 @@ static int skip_pioneer_sync_ep(struct snd_usb_audio *chip,
 	     USB_ENDPOINT_USAGE_DATA &&
 	     (epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
 	     USB_ENDPOINT_USAGE_IMPLICIT_FB))
-		return 0;
-	return 1; /* don't handle with the implicit fb, just skip sync EP */
+		return false;
+
+	return true;
 }
 
 static int __add_generic_implicit_fb(struct snd_usb_audio *chip,
@@ -308,13 +318,11 @@ static int audioformat_implicit_fb_quirk(struct snd_usb_audio *chip,
 	}
 
 	/* Pioneer devices with vendor spec class */
-	if (attr == USB_ENDPOINT_SYNC_ASYNC &&
-	    alts->desc.bInterfaceClass == USB_CLASS_VENDOR_SPEC &&
-	    (USB_ID_VENDOR(chip->usb_id) == 0x2b73 || /* Pioneer */
-	     USB_ID_VENDOR(chip->usb_id) == 0x08e4    /* Pioneer */)) {
-		if (skip_pioneer_sync_ep(chip, fmt, alts))
-			return 1;
-	}
+	if (is_pioneer_implicit_fb(chip, alts))
+		return add_implicit_fb_sync_ep(chip, fmt,
+					       get_endpoint(alts, 1)->bEndpointAddress,
+					       1, alts->desc.bInterfaceNumber,
+					       alts);
 
 	/* Try the generic implicit fb if available */
 	if (chip->generic_implicit_fb)
@@ -335,6 +343,8 @@ static int audioformat_capture_quirk(struct snd_usb_audio *chip,
 	if (p && (p->type == IMPLICIT_FB_FIXED || p->type == IMPLICIT_FB_BOTH))
 		return add_implicit_fb_sync_ep(chip, fmt, p->ep_num, 0,
 					       p->iface, NULL);
+	if (is_pioneer_implicit_fb(chip, alts))
+		return 1; /* skip */
 	return 0;
 }
 
-- 
2.26.2