[PATCH] ASoC: meson: aiu: fifo-spdif: soft reset the S/PDIF datapath on start/stop

[Martin Blumenstingl]

On Fri, Jun 26, 2026 at 10:04 AM Christian Hewitt
<christianshewitt at gmail.com> wrote:
>
> The I2S FIFO soft-resets its fast domain on start (AIU_RST_SOFT bit 0 +
> AIU_I2S_SYNC read in aiu_fifo_i2s_trigger), mirroring the downstream
> vendor driver's audio_out_i2s_enable(). The S/PDIF FIFO has no equivalent:
> it only toggles the IEC958 DCU, so a stale datapath FIFO can be replayed,
> producing the "machine gun noise" buffer underrun - on start when switching
> outputs, and on stop when playback ends. The latter is audible on devices
> with an always-on S/PDIF-fed DAC (e.g. the ES7144 on the WeTek Play2).
>
> The vendor driver resets the IEC958 fast domain (AIU_RST_SOFT bit 2) on
> both enable and disable (audio_hw_958_enable), and when reconfiguring
> (audio_hw_958_reset clears AIU_958_DCU_FF_CTRL then resets). Do the same:
> reset before enabling the DCU on start, and after disabling it on stop.
>
> Signed-off-by: Christian Hewitt <christianshewitt at gmail.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl at googlemail.com>

This matches the vendor driver, references:
- fast-reset SPDIF is triggered on enable and disable: [0]
- fast-reset SPDIF is triggered after all of the configuration is
written, then DCU_FF_CTRL is enabled: [1]

[...]
>         case SNDRV_PCM_TRIGGER_SUSPEND:
>         case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
>         case SNDRV_PCM_TRIGGER_STOP:
>                 fifo_spdif_dcu_enable(component, false);
> +               snd_soc_component_write(component, AIU_RST_SOFT,
> +                                       AIU_RST_SOFT_958_FAST);
It doesn't seem to make any difference, so just for the record:
The vendor driver first triggers AIU_RST_SOFT_958_FAST then disables DCU: [2]


Best regards,
Martin


[0] https://github.com/endlessm/linux-s905x/blob/c1391ba1116aed801aaabfd9c7bbb76fda9801ec/sound/soc/aml/m8/aml_audio_hw.c#L1016
[1] https://github.com/endlessm/linux-s905x/blob/c1391ba1116aed801aaabfd9c7bbb76fda9801ec/sound/soc/aml/m8/aml_audio_hw.c#L979-L983
[2] https://github.com/endlessm/linux-s905x/blob/c1391ba1116aed801aaabfd9c7bbb76fda9801ec/sound/soc/aml/m8/aml_audio_hw.c#L1016-L1018