This is a note to let you know that I've just added the patch titled ALSA: usb-audio: Check available frames for the next packet size to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: alsa-usb-audio-check-available-frames-for-the-next-packet-size.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From d215f63d49da9a8803af3e81acd6cad743686573 Mon Sep 17 00:00:00 2001 From: Takashi Iwai <tiwai@xxxxxxx> Date: Wed, 29 Sep 2021 10:08:41 +0200 Subject: ALSA: usb-audio: Check available frames for the next packet size From: Takashi Iwai <tiwai@xxxxxxx> commit d215f63d49da9a8803af3e81acd6cad743686573 upstream. This is yet more preparation for the upcoming changes. Extend snd_usb_endpoint_next_packet_size() to check the available frames and return -EAGAIN if the next packet size is equal or exceeds the given size. This will be needed for avoiding XRUN during the low latency operation. As of this patch, avail=0 is passed, i.e. the check is skipped and no behavior change. Link: https://lore.kernel.org/r/20210929080844.11583-7-tiwai@xxxxxxx Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- sound/usb/endpoint.c | 51 ++++++++++++++++++++++++++++++++++++--------------- sound/usb/endpoint.h | 3 ++- sound/usb/pcm.c | 2 +- 3 files changed, 39 insertions(+), 17 deletions(-) --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -148,18 +148,23 @@ int snd_usb_endpoint_implicit_feedback_s * This won't be used for implicit feedback which takes the packet size * returned from the sync source */ -static int slave_next_packet_size(struct snd_usb_endpoint *ep) +static int slave_next_packet_size(struct snd_usb_endpoint *ep, + unsigned int avail) { unsigned long flags; + unsigned int phase; int ret; if (ep->fill_max) return ep->maxframesize; spin_lock_irqsave(&ep->lock, flags); - ep->phase = (ep->phase & 0xffff) - + (ep->freqm << ep->datainterval); - ret = min(ep->phase >> 16, ep->maxframesize); + phase = (ep->phase & 0xffff) + (ep->freqm << ep->datainterval); + ret = min(phase >> 16, ep->maxframesize); + if (avail && ret >= avail) + ret = -EAGAIN; + else + ep->phase = phase; spin_unlock_irqrestore(&ep->lock, flags); return ret; @@ -169,20 +174,25 @@ static int slave_next_packet_size(struct * Return the number of samples to be sent in the next packet * for adaptive and synchronous endpoints */ -static int next_packet_size(struct snd_usb_endpoint *ep) +static int next_packet_size(struct snd_usb_endpoint *ep, unsigned int avail) { + unsigned int sample_accum; int ret; if (ep->fill_max) return ep->maxframesize; - ep->sample_accum += ep->sample_rem; - if (ep->sample_accum >= ep->pps) { - ep->sample_accum -= ep->pps; + sample_accum += ep->sample_rem; + if (sample_accum >= ep->pps) { + sample_accum -= ep->pps; ret = ep->packsize[1]; } else { ret = ep->packsize[0]; } + if (avail && ret >= avail) + ret = -EAGAIN; + else + ep->sample_accum = sample_accum; return ret; } @@ -190,16 +200,27 @@ static int next_packet_size(struct snd_u /* * snd_usb_endpoint_next_packet_size: Return the number of samples to be sent * in the next packet + * + * If the size is equal or exceeds @avail, don't proceed but return -EAGAIN + * Exception: @avail = 0 for skipping the check. */ int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep, - struct snd_urb_ctx *ctx, int idx) + struct snd_urb_ctx *ctx, int idx, + unsigned int avail) { - if (ctx->packet_size[idx]) - return ctx->packet_size[idx]; - else if (ep->sync_source) - return slave_next_packet_size(ep); + unsigned int packet; + + packet = ctx->packet_size[idx]; + if (packet) { + if (avail && packet >= avail) + return -EAGAIN; + return packet; + } + + if (ep->sync_source) + return slave_next_packet_size(ep, avail); else - return next_packet_size(ep); + return next_packet_size(ep, avail); } static void call_retire_callback(struct snd_usb_endpoint *ep, @@ -263,7 +284,7 @@ static void prepare_silent_urb(struct sn unsigned int length; int counts; - counts = snd_usb_endpoint_next_packet_size(ep, ctx, i); + counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, 0); length = counts * ep->stride; /* number of silent bytes */ offset = offs * ep->stride + extra * i; urb->iso_frame_desc[i].offset = offset; --- a/sound/usb/endpoint.h +++ b/sound/usb/endpoint.h @@ -46,6 +46,7 @@ void snd_usb_endpoint_free_all(struct sn int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep); int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep, - struct snd_urb_ctx *ctx, int idx); + struct snd_urb_ctx *ctx, int idx, + unsigned int avail); #endif /* __USBAUDIO_ENDPOINT_H */ --- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -1365,7 +1365,7 @@ static void prepare_playback_urb(struct spin_lock_irqsave(&subs->lock, flags); subs->frame_limit += ep->max_urb_frames; for (i = 0; i < ctx->packets; i++) { - counts = snd_usb_endpoint_next_packet_size(ep, ctx, i); + counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, 0); /* set up descriptor */ urb->iso_frame_desc[i].offset = frames * stride; urb->iso_frame_desc[i].length = counts * stride; Patches currently in stable-queue which might be from tiwai@xxxxxxx are queue-5.15/alsa-usb-audio-rename-early_playback_start-flag-with-lowlatency_playback.patch queue-5.15/alsa-usb-audio-disable-low-latency-playback-for-free-wheel-mode.patch queue-5.15/alsa-usb-audio-avoid-killing-in-flight-urbs-during-draining.patch queue-5.15/alsa-usb-audio-less-restriction-for-low-latency-playback-mode.patch queue-5.15/alsa-usb-audio-improved-lowlatency-playback-support.patch queue-5.15/alsa-usb-audio-check-available-frames-for-the-next-packet-size.patch queue-5.15/alsa-usb-audio-switch-back-to-non-latency-mode-at-a-later-point.patch queue-5.15/alsa-usb-audio-fix-packet-size-calculation-regression.patch queue-5.15/alsa-usb-audio-don-t-start-stream-for-capture-at-prepare.patch queue-5.15/alsa-usb-audio-disable-low-latency-mode-for-implicit-feedback-sync.patch queue-5.15/alsa-usb-audio-add-spinlock-to-stop_urbs.patch queue-5.15/alsa-usb-audio-restrict-rates-for-the-shared-clocks.patch