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

Jaroslav Kysela
2026-03-23T14:55:49Z

On 3/23/26 14:34, Péter Ujfalusi wrote:
> Hi,
>
> for years the discussion around jumpy, bursty DMA have been popping up
> and we always concluded that we are missing a good definition and agreed
> way between kernel and user space to handle this.

Hi,

thank you for taking care of this issue.

> Or should we add a new member (carved out from the reserved section of
> hw_params struct) specifically for this purpose, like dma_burst_size,
> which likely going to be equal to fifo_size if both is filled by the driver.

I would not change the fifo_size definition at this moment. It's not directly
related to the sample transfers. This value just describes the additional
latency for streaming.

The new member seems like a good way to go with more universal name like
'chunk_size' (in frames) defining the transfer granularity information for the
PCM buffer I/O.

Jaroslav

--
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.