ASoC: mediatek: use reserved memory or enable buffer pre-allocation

In commit 32c9c06adb ("ASoC: mediatek: disable buffer pre-allocation")
buffer pre-allocation was disabled to accommodate newer platforms that
have a limited reserved memory region for the audio frontend.

Turns out disabling pre-allocation across the board impacts platforms
that don't have this reserved memory region. Buffer allocation failures
have been observed on MT8173 and MT8183 based Chromebooks under low
memory conditions, which results in no audio playback for the user.

Since some MediaTek platforms already have dedicated reserved memory
pools for the audio frontend, the plan is to enable this for all of
them. This requires device tree changes. As a fallback, reinstate the
original policy of pre-allocating audio buffers at probe time of the
reserved memory pool cannot be found or used.

This patch covers the MT8173, MT8183, MT8186 and MT8192 platforms for
now, the reason being that existing MediaTek platform drivers that
supported reserved memory were all platforms that mainly supported
ChromeOS, and is also the set of devices that I can verify.

Fixes: 32c9c06adb ("ASoC: mediatek: disable buffer pre-allocation")
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://patch.msgid.link/20250612074901.4023253-7-wenst@chromium.org
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/mediatek/common/mtk-afe-platform-driver.c

@@ -120,7 +120,9 @@ 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, 0, size);
+	snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, afe->dev,
+				       afe->preallocate_buffers ? size : 0,
+				       size);
 
 	return 0;
 }

sound/soc/mediatek/common/mtk-base-afe.h

@@ -117,6 +117,7 @@ struct mtk_base_afe {
 	struct mtk_base_afe_irq *irqs;
 	int irqs_size;
 	int memif_32bit_supported;
+	bool preallocate_buffers;
 
 	struct list_head sub_dais;
 	struct snd_soc_dai_driver *dai_drivers;

sound/soc/mediatek/mt8173/mt8173-afe-pcm.c

@@ -13,6 +13,7 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/dma-mapping.h>
 #include <linux/pm_runtime.h>
 #include <sound/soc.h>
@@ -1070,6 +1071,12 @@ static int mt8173_afe_pcm_dev_probe(struct platform_device *pdev)
 
 	afe->dev = &pdev->dev;
 
+	ret = of_reserved_mem_device_init(&pdev->dev);
+	if (ret) {
+		dev_info(&pdev->dev, "no reserved memory found, pre-allocating buffers instead\n");
+		afe->preallocate_buffers = true;
+	}
+
 	irq_id = platform_get_irq(pdev, 0);
 	if (irq_id <= 0)
 		return irq_id < 0 ? irq_id : -ENXIO;

sound/soc/mediatek/mt8183/mt8183-afe-pcm.c

@@ -10,6 +10,7 @@
 #include <linux/mfd/syscon.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/pm_runtime.h>
 #include <linux/reset.h>
 
@@ -777,6 +778,12 @@ static int mt8183_afe_pcm_dev_probe(struct platform_device *pdev)
 	afe->dev = &pdev->dev;
 	dev = afe->dev;
 
+	ret = of_reserved_mem_device_init(dev);
+	if (ret) {
+		dev_info(dev, "no reserved memory found, pre-allocating buffers instead\n");
+		afe->preallocate_buffers = true;
+	}
+
 	/* initial audio related clock */
 	ret = mt8183_init_clock(afe);
 	if (ret) {

sound/soc/mediatek/mt8186/mt8186-afe-pcm.c

@@ -10,6 +10,7 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/pm_runtime.h>
 #include <linux/reset.h>
 #include <sound/soc.h>
@@ -2835,6 +2836,12 @@ static int mt8186_afe_pcm_dev_probe(struct platform_device *pdev)
 	afe_priv = afe->platform_priv;
 	afe->dev = &pdev->dev;
 
+	ret = of_reserved_mem_device_init(dev);
+	if (ret) {
+		dev_info(dev, "no reserved memory found, pre-allocating buffers instead\n");
+		afe->preallocate_buffers = true;
+	}
+
 	afe->base_addr = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(afe->base_addr))
 		return PTR_ERR(afe->base_addr);

sound/soc/mediatek/mt8192/mt8192-afe-pcm.c

@@ -12,6 +12,7 @@
 #include <linux/mfd/syscon.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/pm_runtime.h>
 #include <linux/reset.h>
 #include <sound/soc.h>
@@ -2179,6 +2180,12 @@ static int mt8192_afe_pcm_dev_probe(struct platform_device *pdev)
 
 	afe->dev = dev;
 
+	ret = of_reserved_mem_device_init(dev);
+	if (ret) {
+		dev_info(dev, "no reserved memory found, pre-allocating buffers instead\n");
+		afe->preallocate_buffers = true;
+	}
+
 	/* init audio related clock */
 	ret = mt8192_init_clock(afe);
 	if (ret) {