[3.19.y-ckt stable] Patch "usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt8.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From f7a0986f6f8cf0ddfaf616a5e065cedfc624141c Mon Sep 17 00:00:00 2001
From: Peter Chen <peter.chen at freescale.com>
Date: Thu, 30 Jul 2015 13:13:03 +0800
Subject: usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth

commit 913e4a90b6f9687ac0f543e7b632753e4f51c441 upstream.

According to USB Audio Device 2.0 Spec, Ch4.10.1.1:
wMaxPacketSize is defined as follows:
Maximum packet size this endpoint is capable of sending or receiving
when this configuration is selected.
This is determined by the audio bandwidth constraints of the endpoint.

In current code, the wMaxPacketSize is defined as the maximum packet size
for ISO endpoint, and it will let the host reserve much more space than
it really needs, so that we can't let more endpoints work together at
one frame.

We find this issue when we try to let 4 f_uac2 gadgets work together [1]
at FS connection.

[1]http://www.spinics.net/lists/linux-usb/msg123478.html

Acked-by: Daniel Mack <zonque at gmail.com>
Cc: andrzej.p at samsung.com
Cc: Daniel Mack <zonque at gmail.com>
Cc: tiwai at suse.de
Cc: Alan Stern <stern at rowland.harvard.edu>
Signed-off-by: Peter Chen <peter.chen at freescale.com>
Signed-off-by: Felipe Balbi <balbi at ti.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/usb/gadget/function/f_uac2.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index df02947..3879c92 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -975,6 +975,29 @@ free_ep(struct uac2_rtd_params *prm, struct usb_ep *ep)
 			"%s:%d Error!\n", __func__, __LINE__);
 }

+static void set_ep_max_packet_size(const struct f_uac2_opts *uac2_opts,
+	struct usb_endpoint_descriptor *ep_desc,
+	unsigned int factor, bool is_playback)
+{
+	int chmask, srate, ssize;
+	u16 max_packet_size;
+
+	if (is_playback) {
+		chmask = uac2_opts->p_chmask;
+		srate = uac2_opts->p_srate;
+		ssize = uac2_opts->p_ssize;
+	} else {
+		chmask = uac2_opts->c_chmask;
+		srate = uac2_opts->c_srate;
+		ssize = uac2_opts->c_ssize;
+	}
+
+	max_packet_size = num_channels(chmask) * ssize *
+		DIV_ROUND_UP(srate, factor / (1 << (ep_desc->bInterval - 1)));
+	ep_desc->wMaxPacketSize = cpu_to_le16(min(max_packet_size,
+				le16_to_cpu(ep_desc->wMaxPacketSize)));
+}
+
 static int
 afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 {
@@ -1070,10 +1093,14 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 	uac2->p_prm.uac2 = uac2;
 	uac2->c_prm.uac2 = uac2;

+	/* Calculate wMaxPacketSize according to audio bandwidth */
+	set_ep_max_packet_size(uac2_opts, &fs_epin_desc, 1000, true);
+	set_ep_max_packet_size(uac2_opts, &fs_epout_desc, 1000, false);
+	set_ep_max_packet_size(uac2_opts, &hs_epin_desc, 8000, true);
+	set_ep_max_packet_size(uac2_opts, &hs_epout_desc, 8000, false);
+
 	hs_epout_desc.bEndpointAddress = fs_epout_desc.bEndpointAddress;
-	hs_epout_desc.wMaxPacketSize = fs_epout_desc.wMaxPacketSize;
 	hs_epin_desc.bEndpointAddress = fs_epin_desc.bEndpointAddress;
-	hs_epin_desc.wMaxPacketSize = fs_epin_desc.wMaxPacketSize;

 	ret = usb_assign_descriptors(fn, fs_audio_desc, hs_audio_desc, NULL);
 	if (ret)
--
1.9.1