Re: [alsa-devel] [PATCH] fsl_ssi: set fifo watermark to more reliable value

[Fabio Estevam]

On Tue, Jan 3, 2017 at 4:22 PM, Caleb Crome <ccrome@xxxxxxxxx> wrote:
> From: Caleb Crome <caleb@xxxxxxxxx>
>
> The fsl_ssi fifo watermark is by default set to 2 free spaces (i.e.
> activate DMA on FIFO when only 2 spaces are left.)  This means the
> DMA must service the fifo within 2 audio samples, which is just not
> enough time  for many use cases with high data rate.  In many
> configurations the audio channel slips (causing l/r swap in stereo
> configurations, or channel slipping in multi-channel configurations).
>
> This patch gives more breathing room and allows the SSI to operate
> reliably by changing the fifio refill watermark to 8.
>
> There is no change in behavior for older chips (with an 8-deep fifo).
> Only the newer chips with a 15-deep fifo get the new behavior. I
> suspect a new fifo depth setting could be optimized on the older
> chips too, but I have not tested.
>
> Signed-off-by: Caleb Crome <caleb@xxxxxxxxx>

Reviewed-by: Fabio Estevam <fabio.estevam@xxxxxxx>