[PATCH v2 1/1] usb: gadget: f_uac2: finalize wMaxPacketSize according to bandwidth

[Peter Chen <peter.chen@freescale.com>]

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

Cc: andrzej.p@samsung.com
Cc: zonque@gmail.com
Cc: tiwai@suse.de
Cc: <stable@vger.kernel.org> #v3.18+
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
---

Changes for v2:
- Using DIV_ROUND_UP to calculate max packet size

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

diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c
index 6d3eb8b..6eaa4c4 100644
--- a/drivers/usb/gadget/function/f_uac2.c
+++ b/drivers/usb/gadget/function/f_uac2.c
@@ -987,6 +987,7 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 	struct f_uac2_opts *uac2_opts;
 	struct usb_string *us;
 	int ret;
+	u16 c_max_packet_size, p_max_packet_size;
 
 	uac2_opts = container_of(fn->fi, struct f_uac2_opts, func_inst);
 
@@ -1070,6 +1071,19 @@ 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 */
+	c_max_packet_size = uac2_opts->c_chmask * uac2_opts->c_ssize
+		* DIV_ROUND_UP(uac2_opts->c_srate, 1000);
+	p_max_packet_size = uac2_opts->p_chmask * uac2_opts->p_ssize
+		* DIV_ROUND_UP(uac2_opts->p_srate, 1000);
+	if ((c_max_packet_size > fs_epout_desc.wMaxPacketSize) ||
+		(p_max_packet_size > fs_epin_desc.wMaxPacketSize)) {
+		dev_err(dev, "parameters are incorrect\n");
+		goto err;
+	}
+	fs_epin_desc.wMaxPacketSize = cpu_to_le16(c_max_packet_size);
+	fs_epout_desc.wMaxPacketSize = cpu_to_le16(p_max_packet_size);
+
 	hs_epout_desc.bEndpointAddress = fs_epout_desc.bEndpointAddress;
 	hs_epout_desc.wMaxPacketSize = fs_epout_desc.wMaxPacketSize;
 	hs_epin_desc.bEndpointAddress = fs_epin_desc.bEndpointAddress;
-- 
1.9.1