[PATCH 5.14 004/151] usb: gadget: f_uac2: fixed EP-IN wMaxPacketSize

[Greg Kroah-Hartman]

From: Pavel Hofman <pavel.hofman@xxxxxxxxxxx>

commit 0560c9c552c1815e7b480bc11fd785fefc82bb27 upstream.

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.

Fixes: e89bb4288378 ("usb: gadget: u_audio: add real feedback implementation")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Tested-by: Henrik Enquist <henrik.enquist@xxxxxxxxx>
Tested-by: Jack Pham <jackp@xxxxxxxxxxxxxx>
Signed-off-by: Pavel Hofman <pavel.hofman@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210924080027.5362-1-pavel.hofman@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/usb/gadget/function/f_uac2.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -593,11 +593,17 @@ static int set_ep_max_packet_size(const
 		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));