[PATCH] ALSA: usb-audio: Apply async workaround for Scarlett 2i4 2nd gen
Takashi Iwai
tiwai at suse.de
Thu Apr 23 09:22:36 CEST 2020
On Thu, 23 Apr 2020 01:45:01 +0200,
Alexander Tsoy wrote:
>
> В Ср, 22/04/2020 в 22:28 +0200, Takashi Iwai пишет:
> > On Wed, 22 Apr 2020 21:26:23 +0200,
> > Alexander Tsoy wrote:
> > > В Ср, 22/04/2020 в 20:55 +0200, Gregor Pintar пишет:
> > > > On Wed, 22 Apr 2020 Alexander Tsoy wrote:
> > > > > В Вт, 21/04/2020 в 21:31 +0200, Takashi Iwai пишет:
> > > > > > I wonder, though, whether we can correct the rounding error
> > > > > > in
> > > > > > the
> > > > > > driver code, too.
> > > > >
> > > > > I'm not sure if it's possible with currently used Q16.16
> > > > > arithmetic.
> > > >
> > > > Maybe calculate fixed correction shifts (like it would be
> > > > feedback)?
> > > > Something like leap year.
> > > >
> > > > In endpoint.c:
> > > > static inline unsigned get_usb_high_speed_rate(unsigned int rate)
> > > > {
> > > > return ((rate << 10) + 62) / 125;
> > > > }
> > > > I guess 62 tries to round it, but exact number is needed. So
> > > > exact
> > > > value for
> > > > 44100 should be 361267.2. For 48000 it is 360448.
> > > > If only we can deliver that 0.2 by shifting rate somehow?
> > > >
> > > > At least maybe it would be better to disable sample rates that do
> > > > not
> > > > divide
> > > > by 1000 on SYNC playback endpoints, if there are others sample
> > > > rates.
> > > >
> > > > But I'm not familar with the code or USB.
> > >
> > > I think instead of accumulating the fractional part of fs/fps in
> > > Q16.16
> > > format we should accumulating remainder of division fs/fps.
> > >
> > > So for 44100 Hz and High Speed USB the calculations would be:
> > >
> > > fs = 44100
> > > fps = 8000
> > > rem = 44100 % 8000 = 4100
> > > accum = 0
> > > packet_size_min = 44100 / 8000 = 5
> > > packet_size_max = 44100 + (8000 - 1) / 8000 = 6
> > >
> > >
> > > 1. accum += rem = 4100
> > > accum < fps => packet_size = packet_size_min = 5
> > >
> > > 2. accum += rem = 8200
> > > accum >= fps => {
> > > packet_size = packet_size_max = 6
> > > accum -= fps = 200
> > > }
> > >
> > > 3. accum += rem = 4300
> > > accum < fps => packet_size = packet_size_min = 5
> > >
> > > ...
> > >
> > > 80. accum += rem = 8000
> > > accum >= fps => {
> > > packet_size = packet_size_max = 6
> > > accum -= fps = 0
> > > }
> > > ...
> >
> > Yeah, something like that is what I had in my mind.
> > It'd be greatly appreciated if someone can experiment it.
> > Unfortunately I have no proper USB-audio device now at hands...
>
> OK, here is a quick hacky patch, that seems to work for me:
Awesome, thanks!
The patch looks good enough. A minor fix would be reset sample_accum
at snd_usb_pcm_prepare().
If someone can test more and it shows the positive result, I'd happy
take it.
thanks,
Takashi
> diff --git a/sound/usb/card.h b/sound/usb/card.h
> index 395403a2d33f..fc5e3e391219 100644
> --- a/sound/usb/card.h
> +++ b/sound/usb/card.h
> @@ -84,6 +84,10 @@ struct snd_usb_endpoint {
> dma_addr_t sync_dma; /* DMA address of syncbuf */
>
> unsigned int pipe; /* the data i/o pipe */
> + unsigned int framesize[2]; /* min/max frame size in samples */
> + unsigned int sample_rem; /* remainder of division fs/fps */
> + unsigned int sample_accum; /* fs % fps accumulator */
> + unsigned int fps; /* frames per second */
> unsigned int freqn; /* nominal sampling rate in fs/fps in Q16.16 format */
> unsigned int freqm; /* momentary sampling rate in fs/fps in Q16.16 format */
> int freqshift; /* how much to shift the feedback value to get Q16.16 */
> diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
> index 4a9a2f6ef5a4..e0e4dc5cfe0e 100644
> --- a/sound/usb/endpoint.c
> +++ b/sound/usb/endpoint.c
> @@ -124,12 +124,12 @@ int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep)
>
> /*
> * For streaming based on information derived from sync endpoints,
> - * prepare_outbound_urb_sizes() will call next_packet_size() to
> + * prepare_outbound_urb_sizes() will call slave_next_packet_size() to
> * determine the number of samples to be sent in the next packet.
> *
> - * For implicit feedback, next_packet_size() is unused.
> + * For implicit feedback, slave_next_packet_size() is unused.
> */
> -int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep)
> +int snd_usb_endpoint_slave_next_packet_size(struct snd_usb_endpoint *ep)
> {
> unsigned long flags;
> int ret;
> @@ -146,6 +146,32 @@ int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep)
> return ret;
> }
>
> +/*
> + * For adaptive and synchronous endpoints, prepare_outbound_urb_sizes()
> + * will call next_packet_size() to determine the number of samples to be
> + * sent in the next packet.
> + */
> +int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep)
> +{
> + unsigned long flags;
> + int ret;
> +
> + if (ep->fill_max)
> + return ep->maxframesize;
> +
> + spin_lock_irqsave(&ep->lock, flags);
> + ep->sample_accum += ep->sample_rem;
> + if (ep->sample_accum >= ep->fps) {
> + ep->sample_accum -= ep->fps;
> + ret = ep->framesize[1];
> + } else {
> + ret = ep->framesize[0];
> + }
> + spin_unlock_irqrestore(&ep->lock, flags);
> +
> + return ret;
> +}
> +
> static void retire_outbound_urb(struct snd_usb_endpoint *ep,
> struct snd_urb_ctx *urb_ctx)
> {
> @@ -190,6 +216,8 @@ static void prepare_silent_urb(struct snd_usb_endpoint *ep,
>
> if (ctx->packet_size[i])
> counts = ctx->packet_size[i];
> + else if (ep->sync_master)
> + counts = snd_usb_endpoint_slave_next_packet_size(ep);
> else
> counts = snd_usb_endpoint_next_packet_size(ep);
>
> @@ -874,10 +902,17 @@ int snd_usb_endpoint_set_params(struct snd_usb_endpoint *ep,
> ep->maxpacksize = fmt->maxpacksize;
> ep->fill_max = !!(fmt->attributes & UAC_EP_CS_ATTR_FILL_MAX);
>
> - if (snd_usb_get_speed(ep->chip->dev) == USB_SPEED_FULL)
> + if (snd_usb_get_speed(ep->chip->dev) == USB_SPEED_FULL) {
> ep->freqn = get_usb_full_speed_rate(rate);
> - else
> + ep->fps = 1000;
> + } else {
> ep->freqn = get_usb_high_speed_rate(rate);
> + ep->fps = 8000;
> + }
> +
> + ep->sample_rem = rate % ep->fps;
> + ep->framesize[0] = rate / ep->fps;
> + ep->framesize[1] = (rate + (ep->fps - 1)) / ep->fps;
>
> /* calculate the frequency in 16.16 format */
> ep->freqm = ep->freqn;
> diff --git a/sound/usb/endpoint.h b/sound/usb/endpoint.h
> index 63a39d4fa8d8..d23fa0a8c11b 100644
> --- a/sound/usb/endpoint.h
> +++ b/sound/usb/endpoint.h
> @@ -28,6 +28,7 @@ void snd_usb_endpoint_release(struct snd_usb_endpoint *ep);
> void snd_usb_endpoint_free(struct snd_usb_endpoint *ep);
>
> int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep);
> +int snd_usb_endpoint_slave_next_packet_size(struct snd_usb_endpoint *ep);
> int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep);
>
> void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep,
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index a4e4064f9aee..b50965ab3b3a 100644
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -1579,6 +1579,8 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
> for (i = 0; i < ctx->packets; i++) {
> if (ctx->packet_size[i])
> counts = ctx->packet_size[i];
> + else if (ep->sync_master)
> + counts = snd_usb_endpoint_slave_next_packet_size(ep);
> else
> counts = snd_usb_endpoint_next_packet_size(ep);
>
> --
> 2.25.3
>
>
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