usb: gadget: f_uac2: fixed EP-IN wMaxPacketSize

Async feedback patches broke enumeration on Windows 10 previously fixed
by commit 789ea77 ("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: e89bb42 ("usb: gadget: u_audio: add real feedback implementation")
Cc: stable <[email protected]>
Tested-by: Henrik Enquist <[email protected]>
Tested-by: Jack Pham <[email protected]>
Signed-off-by: Pavel Hofman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: pavhofman

drivers/usb/gadget/function/f_uac2.c

@@ -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));