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]. [1]http://www.spinics.net/lists/linux-usb/msg123478.html Cc: <stable@xxxxxxxxxxxxxxx> #v3.18+ Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Peter Chen <peter.chen@xxxxxxxxxxxxx> --- drivers/usb/gadget/function/f_uac2.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c index 6d3eb8b..0ed6f0e 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 +1071,29 @@ 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 + * uac2_opts->c_srate / 1000; + p_max_packet_size = uac2_opts->p_chmask * uac2_opts->p_ssize + * 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; + } + /* + * Keep max packet size is multiplier of 4, and + * a little larger than bandwidth. + * Eg, for frame rate 44100, 1 channel, and 16 bits data + * we need to reserve more than 44 * 2 bytes. + */ + c_max_packet_size += (4 - (c_max_packet_size % 4)); + fs_epin_desc.wMaxPacketSize = min(cpu_to_le16(c_max_packet_size), + fs_epin_desc.wMaxPacketSize); + p_max_packet_size += (4 - (p_max_packet_size % 4)); + fs_epout_desc.wMaxPacketSize = min(cpu_to_le16(p_max_packet_size), + fs_epout_desc.wMaxPacketSize); + 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html