On Wed, 17 Jun 2020 12:51:05 +0200,
Mark Hills wrote:
>
> On Tue, 16 Jun 2020, Takashi Iwai wrote:
>
> > On Tue, 16 Jun 2020 16:01:11 +0200,
> > Mark Hills wrote:
> > >
> > > On Tue, 16 Jun 2020, Takashi Iwai wrote:
> > >
> > > > On Tue, 16 Jun 2020 15:17:43 +0200,
> > > > Mark Hills wrote:
> > > > >
> > > > > +/* Update software pointer to match the hardware
> > > > > + *
> > > > > + * Return: 1 if we crossed a period threshold, otherwise 0
> > > > > + */
> > > > > +static int snd_echo_poll_substream(struct snd_pcm_substream *substream)
> > > >
> > > > This is a bit confusing name. One would imagine from the function
> > > > name as if it were about the handling of poll() syscall.
> > >
> > > Poll felt intuitive to me; maybe from FreeBSD where network drivers can
> > > poll on a timer instead of interrupts. I do know about poll(), though.
> > >
> > > How about snd_echo_update_substream()?
> >
> > Yes, it's more self-explanatory. Or even better
> > snd_echo_update_substream_position() :)
>
> Out of interest, these are static but the names are globally qualified. I
> see this elsewhere, so I followed, but is this agreed convention?
>
> Because it could be update_substream_position() :)
It's fine to use any name for a local function.
> > > > > +{
> > > > > + struct snd_pcm_runtime *runtime = substream->runtime;
> > > > > + struct audiopipe *pipe = runtime->private_data;
> > > > > + unsigned counter, step, period, last_period;
> > > > > + size_t buffer_bytes;
> > > > > +
> > > > > + if (pipe->state != PIPE_STATE_STARTED)
> > > > > + return 0;
> > > > > +
> > > > > + counter = le32_to_cpu(*pipe->dma_counter);
> > > > > +
> > > > > + period = bytes_to_frames(runtime, counter)
> > > > > + / runtime->period_size;
> > > > > + last_period = bytes_to_frames(runtime, pipe->last_counter)
> > > > > + / runtime->period_size;
> > > > > +
> > > > > + if (period == last_period)
> > > > > + return 0; /* don't do any work yet */
> > > > > +
> > > > > + step = counter - pipe->last_counter;
> > > > > + pipe->last_counter = counter;
> > > >
> > > > Dose this calculation consider the overlap of 32bit integer of the
> > > > counter? (I'm not sure whether the old code did it right, though.)
> > >
> > > I believe it does, since (small - big) as unsigned gives small value. And
> > > period is checked only for equality (not greater than). I'll add a comment
> > > as such. I have run it with long streams.
> >
> > The problem is that the last_period calculation can be wrong if the
> > period size isn't aligned. e.g. when period size is 44100, around the
> > boundary position, it gets a different last_period value although it
> > still in the same period.
>
> Agreed, yes.
>
> In which case I think it's clearer to not infer anything about periods
> from the current counter or position, and (effectively) accumulate it.
>
> Would you please make suggestions on the code below?
>
> Because it allowed for further simplification whilst fixing the bugs.
>
> In the end, modulo became clearer than loops and I think it has the bonus
> of being less risky should the counter make a large step.
>
> I'll run for a longer test today.
>
> ---
>
> /* Update software pointer to match the hardware
> *
> * \pre chip->lock is held
> */
> static void snd_echo_update_substream_position(struct echoaudio *chip,
> struct snd_pcm_substream *substream)
> {
> struct snd_pcm_runtime *runtime = substream->runtime;
> struct audiopipe *pipe = runtime->private_data;
> u32 counter, step;
> size_t period_bytes;
>
> if (pipe->state != PIPE_STATE_STARTED)
> return;
>
> period_bytes = frames_to_bytes(runtime, runtime->period_size);
>
> counter = le32_to_cpu(*pipe->dma_counter);
>
> step = counter - pipe->last_counter; /* handles wrapping of counter */
> step -= step % period_bytes; /* acknowledge whole periods only */
>
> if (step == 0)
> return; /* haven't advanced a whole period yet */
> pipe->last_counter += step; /* does not always wrap on a period */
> pipe->position += step;
>
> /* wraparound the buffer */
> pipe->position %= frames_to_bytes(runtime, runtime->buffer_size);
>
> /* notify only once, even if multiple periods elapsed */
> spin_unlock(&chip->lock);
> snd_pcm_period_elapsed(substream);
> spin_lock(&chip->lock);
> }
>
> static irqreturn_t snd_echo_interrupt(int irq, void *dev_id)
> {
> struct echoaudio *chip = dev_id;
> int ss, st;
>
> spin_lock(&chip->lock);
> st = service_irq(chip);
> if (st < 0) {
> spin_unlock(&chip->lock);
> return IRQ_NONE;
> }
> /* The hardware doesn't tell us which substream caused the irq,
> thus we have to check all running substreams. */
> for (ss = 0; ss < DSP_MAXPIPES; ss++) {
> struct snd_pcm_substream *substream;
>
> substream = chip->substream[ss];
> if (substream)
> snd_echo_update_substream_position(chip, substream);
> }
> spin_unlock(&chip->lock);
>
> #ifdef ECHOCARD_HAS_MIDI
> if (st > 0 && chip->midi_in) {
> snd_rawmidi_receive(chip->midi_in, chip->midi_buffer, st);
> dev_dbg(chip->card->dev, "rawmidi_iread=%d\n", st);
> }
> #endif
> return IRQ_HANDLED;
> }
>
> static snd_pcm_uframes_t pcm_pointer(struct snd_pcm_substream *substream)
> {
> struct snd_pcm_runtime *runtime = substream->runtime;
> struct audiopipe *pipe = runtime->private_data;
>
> return bytes_to_frames(runtime, pipe->position);
I guess this misses the update of the precise position; in your code,
pipe->position gets updated only with the period size at irq handler.
IMO, we should have the code like:
static bool update_stream_position(struct snd_pcm_substream *substream)
{
// update pipe->position and others, returns true if period elapsed
}
static irqreturn_t snd_echo_interrupt()
{
spin_lock(&chip->lock);
....
if (update_stream_position(substream)) {
spin_unlock(&chip->lock);
snd_pcm_period_elapsed(substream);
spin_lock(&chip->lock);
}
....
spin_unlock(&chip->lock);
return IRQ_HANDLED;
}
static snd_pcm_uframes_t pcm_pointer(struct snd_pcm_substream *substream)
{
....
update_stream_position(substream);
return bytes_to_frames(runtime, pipe->position);
}
Note that snd_pcm_period_elapsed() isn't needed (must not be done)
from the pointer callback. The PCM core would detect and handle
properly if the period gets elapsed there.
thanks,
Takashi
