[PATCH 3/3] echoaudio: Address bugs in the interrupt handling

[Giuliano Pochini]

On Tue, 16 Jun 2020 14:17:43 +0100
Mark Hills <mark at xwax.org> wrote:

> Distorted audio appears occasionally, affecting either playback
> or capture and requiring the affected substream to be closed by
> all applications and re-opened.

Yes, it also happens here very rarely (one time every some months) and I failed to reproduce the problem.


> The best way I have found to reproduce the bug is to use dmix in
> combination with Chromium, which opens the audio device multiple
> times in threads. Anecdotally, the problems appear to have increased
> with faster CPUs.
> 
> Since applying this patch I have not had problems, where previously
> they would occur several times a day.
> 
> This patch addresses the following issues:
> 
> * Check for progress using the counter from the hardware, not after
>   it has been truncated to the buffer.
> 
>   There appears to be a possible bug if a whole ringbuffer advances
>   between interrupts, it goes unnoticed.

In that case the stream must be restarted anyway due to xrun.


> * Remove chip->last_period:
> 
>   It's trivial to derive from pipe->last_counter, and inside pipe
>   is where it more logically belongs. This has less scope for bugs
>   as it is not wrapped to the buffer length.

Ok.


> * Remove the accessing of pipe->dma_counter twice in the interrupt
>   handler:

Why twice?


> +static int snd_echo_poll_substream(struct snd_pcm_substream *substream)
> [...]
>  static irqreturn_t snd_echo_interrupt(int irq, void *dev_id)
> [...]

Looks fine to me.


-- 
Giuliano.