patch "usb: gadget: f_uac2: fixed EP-IN wMaxPacketSize" added to usb-linus

This is a note to let you know that I've just added the patch titled

usb: gadget: f_uac2: fixed EP-IN wMaxPacketSize

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 0560c9c552c1815e7b480bc11fd785fefc82bb27 Mon Sep 17 00:00:00 2001
From: Pavel Hofman <[email protected]>
Date: Fri, 24 Sep 2021 10:00:27 +0200
Subject: usb: gadget: f_uac2: fixed EP-IN wMaxPacketSize

Async feedback patches broke enumeration on Windows 10 previously fixed by commit 789ea77310f0 ("usb: gadget: f_uac2: always increase endpoint max_packet_size by one audio slot").

While the existing calculation for EP OUT capture for async mode yields size+1 frame due to uac2_opts->fb_max > 0, playback side lost the +1 feature. Therefore the +1 frame addition must be re-introduced for playback. Win10 enumerates the device only when both EP IN and EP OUT max packet sizes are (at least) +1 frame.

---
 drivers/usb/gadget/function/f_uac2.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

index be864560bfea..ef55b8bb5870 100644
@@ -674,11 +674,17 @@ static int set_ep_max_packet_size(const struct f_uac2_opts *uac2_opts,
 		ssize = uac2_opts->c_ssize;
 	}
 
-	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC))
+	if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC)) {
+	  // Win10 requires max packet size + 1 frame
 		srate = srate * (1000 + uac2_opts->fb_max) / 1000;
-
-	max_size_bw = num_channels(chmask) * ssize *
-		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
+		// updated srate is always bigger, therefore DIV_ROUND_UP always yields +1
+		max_size_bw = num_channels(chmask) * ssize *
+			(DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1))));
+	} else {
+		// adding 1 frame provision for Win10
+		max_size_bw = num_channels(chmask) * ssize *
+			(DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1))) + 1);
+	}
 	ep_desc->wMaxPacketSize = cpu_to_le16(min_t(u16, max_size_bw,
 						    max_size_ep));
 

2.33.0