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@xxxxxxxxxxx Cc: Daniel Mack <zonque@xxxxxxxxx> Cc: tiwai@xxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> #v3.18+ Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Peter Chen <peter.chen@xxxxxxxxxxxxx> --- Changes for v3: - Consider 'bInterval' to calculate wMaxPacketSize - playback endpoint is IN ep, and capture endpoint is OUT ep Changes for v2: - Using DIV_ROUND_UP to calculate max packet size drivers/usb/gadget/function/f_uac2.c | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) diff --git a/drivers/usb/gadget/function/f_uac2.c b/drivers/usb/gadget/function/f_uac2.c index 6d3eb8b..51ca32d 100644 --- a/drivers/usb/gadget/function/f_uac2.c +++ b/drivers/usb/gadget/function/f_uac2.c @@ -987,6 +987,8 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn) struct f_uac2_opts *uac2_opts; struct usb_string *us; int ret; + u16 max_packet_size; + struct usb_endpoint_descriptor *ep_desc; uac2_opts = container_of(fn->fi, struct f_uac2_opts, func_inst); @@ -1070,10 +1072,37 @@ 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 */ + ep_desc = &fs_epin_desc; + max_packet_size = num_channels(uac2_opts->p_chmask) * + uac2_opts->p_ssize * DIV_ROUND_UP(uac2_opts->p_srate, + 1000 / (1 << (ep_desc->bInterval - 1))); + ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size), + ep_desc->wMaxPacketSize); + + ep_desc = &fs_epout_desc; + max_packet_size = num_channels(uac2_opts->c_chmask) * + uac2_opts->c_ssize * DIV_ROUND_UP(uac2_opts->c_srate, + 1000 / (1 << (ep_desc->bInterval - 1))); + ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size), + ep_desc->wMaxPacketSize); + + ep_desc = &hs_epin_desc; + max_packet_size = num_channels(uac2_opts->p_chmask) * + uac2_opts->p_ssize * DIV_ROUND_UP(uac2_opts->p_srate, + 8000 / (1 << (ep_desc->bInterval - 1))); + ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size), + ep_desc->wMaxPacketSize); + + ep_desc = &hs_epout_desc; + max_packet_size = num_channels(uac2_opts->c_chmask) * + uac2_opts->c_ssize * DIV_ROUND_UP(uac2_opts->c_srate, + 8000 / (1 << (ep_desc->bInterval - 1))); + ep_desc->wMaxPacketSize = min(cpu_to_le16(max_packet_size), + ep_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; - 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 -- 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