Re: (re)use and (re)definition of snd_pcm_hw_params->fifo_size for 'jumpy DMA'

Péter Ujfalusi
2026-04-23T05:05:36Z

On 22/04/2026 17:19, Péter Ujfalusi wrote:

> Hrm, so this is a driver scoped refine, right? Based on the requested
> period size and a flag (SNDRV_PCM_HW_PARAMS_LATENCY_AWARE?) the driver
> refines the period size based on it's jumpyDMA capabilities?
>
> But in this example the application will have no knowledge still how the
> DMA will move, the DMA will initially move 30ms and after that, every
> 5ms it moves 5ms, so the driver should be refining to 5ms period size, 6
> initial periods and 1 period step, no.
>
> Or with my favorite examples:
> 4ms initial burst w/ 1ms steps will refine to 1ms periods, 4 init and 1
> step.
> 100ms initial burst w/ 96ms steps will refine to... I'm not sure

4ms period size, 25 init periods, 24 step periods?

and same for
> 40ms initial burst w/ 36ms steps.

4ms period size, 10 init periods, 9 step periods?

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Péter