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: [email protected] Cc: Daniel Mack <[email protected]> Cc: [email protected] Cc: <[email protected]> #v3.18+ Cc: Alan Stern <[email protected]> Signed-off-by: Peter Chen <[email protected]> --- Changes for v4: - Add helper set_ep_max_packet_size to calculate max packet size 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 5318615..6a8e0d2 100644 --- a/drivers/usb/gadget/function/f_uac2.c +++ b/drivers/usb/gadget/function/f_uac2.c @@ -975,6 +975,31 @@ free_ep(struct uac2_rtd_params *prm, struct usb_ep *ep) "%s:%d Error!\n", __func__, __LINE__); } +static void set_ep_max_packet_size (struct f_uac2_opts *uac2_opts, + struct usb_endpoint_descriptor *ep_desc, unsigned int factor) +{ + int chmask; + int srate; + int ssize; + u16 max_packet_size; + + if (ep_desc == &fs_epin_desc || ep_desc == &hs_epin_desc) { + chmask = uac2_opts->p_chmask; + srate = uac2_opts->p_srate; + ssize = uac2_opts->p_ssize; + } else { + WARN_ON (ep_desc != &fs_epout_desc && ep_desc != &hs_epout_desc); + 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 = min(cpu_to_le16(max_packet_size), + ep_desc->wMaxPacketSize); +} + static int afunc_bind(struct usb_configuration *cfg, struct usb_function *fn) { @@ -1070,10 +1095,14 @@ 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); + set_ep_max_packet_size(uac2_opts, &fs_epout_desc, 1000); + set_ep_max_packet_size(uac2_opts, &hs_epin_desc, 8000); + set_ep_max_packet_size(uac2_opts, &hs_epout_desc, 8000); + 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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
