[PATCH] ASoC: mediatek: disable buffer pre-allocation

[AngeloGioacchino Del Regno]

Il 19/12/24 11:53, Chen-Yu Tsai ha scritto:
> On Chromebooks based on Mediatek MT8195 or MT8188, the audio frontend
> (AFE) is limited to accessing a very small window (1 MiB) of memory,
> which is described as a reserved memory region in the device tree.
> 
> On these two platforms, the maximum buffer size is given as 512 KiB.
> The MediaTek common code uses the same value for preallocations. This
> means that only the first two PCM substreams get preallocations, and
> then the whole space is exhausted, barring any other substreams from
> working. Since the substreams used are not always the first two, this
> means audio won't work correctly.
> 
> This is observed on the MT8188 Geralt Chromebooks, on which the
> "mediatek,dai-link" property was dropped when it was upstreamed. That
> property causes the driver to only register the PCM substreams listed
> in the property, and in the order given.
> 
> Instead of trying to compute an optimal value and figuring out which
> streams are used, simply disable preallocation. The PCM buffers are
> managed by the core and are allocated and released on the fly. There
> should be no impact to any of the other MediaTek platforms.
> 
> Signed-off-by: Chen-Yu Tsai <wenst at chromium.org>

No there's no impact on the older ones, it's fine and I agree.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>

> ---
>   sound/soc/mediatek/common/mtk-afe-platform-driver.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/soc/mediatek/common/mtk-afe-platform-driver.c b/sound/soc/mediatek/common/mtk-afe-platform-driver.c
> index 9b72b2a7ae91..6b6330583941 100644
> --- a/sound/soc/mediatek/common/mtk-afe-platform-driver.c
> +++ b/sound/soc/mediatek/common/mtk-afe-platform-driver.c
> @@ -120,8 +120,8 @@ int mtk_afe_pcm_new(struct snd_soc_component *component,
>   	struct mtk_base_afe *afe = snd_soc_component_get_drvdata(component);
>   
>   	size = afe->mtk_afe_hardware->buffer_bytes_max;
> -	snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV,
> -				       afe->dev, size, size);
> +	snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, afe->dev, 0, size);
> +
>   	return 0;
>   }
>   EXPORT_SYMBOL_GPL(mtk_afe_pcm_new);