drm/apple: audio: Defer DMA channel acquisition to device open

Allow the DMA device driver to probe late, and still create the sound
device upfront. Instead try to request the DMA channel on first PCM
open. This should be safe as long as we bail early and don't allow the
process to continue to configuring buffers (since that requires the DMA
to be configured).

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

drivers/gpu/drm/apple/audio.c

@@ -212,17 +212,47 @@ static int dcpaud_rule_rate(struct snd_pcm_hw_params *params,
         return snd_interval_rate_bits(r, hits.rates);
 }
 
+static int dcpaud_init_dma(struct dcp_audio *dcpaud)
+{
+	struct dma_chan *chan;
+	if (dcpaud->chan)
+		return 0;
+
+	chan = of_dma_request_slave_channel(dcpaud->dev->of_node, "tx");
+	/* squelch dma channel request errors, the driver will try again alter */
+	if (!chan) {
+		dev_warn(dcpaud->dev, "audio TX DMA channel request failed\n");
+		return -ENXIO;
+	} else if (chan == ERR_PTR(-EPROBE_DEFER)) {
+		dev_info(dcpaud->dev, "audio TX DMA channel is not ready yet\n");
+		return -ENXIO;
+	} else if (IS_ERR(chan)) {
+		dev_warn(dcpaud->dev, "audio TX DMA channel request failed: %ld\n", PTR_ERR(chan));
+		return PTR_ERR(chan);
+	}
+	dcpaud->chan = chan;
+
+	snd_pcm_set_managed_buffer(dcpaud->substream, SNDRV_DMA_TYPE_DEV_IRAM,
+				   dcpaud->chan->device->dev, 1024 * 1024,
+				   SIZE_MAX);
+
+	return 0;
+}
+
 static int dcp_pcm_open(struct snd_pcm_substream *substream)
 {
 	struct dcp_audio *dcpaud = substream->pcm->private_data;
-	struct dma_chan *chan = dcpaud->chan;
 	struct snd_dmaengine_dai_dma_data dma_data = {
 		.flags = SND_DMAENGINE_PCM_DAI_FLAG_PACK,
 	};
 	struct snd_pcm_hardware hw;
 	int ret;
 
 	mutex_lock(&dcpaud->data_lock);
+	ret = dcpaud_init_dma(dcpaud);
+	if (ret < 0)
+		return ret;
+
 	if (!dcpaud->connected) {
 		mutex_unlock(&dcpaud->data_lock);
 		return -ENXIO;
@@ -254,12 +284,12 @@ static int dcp_pcm_open(struct snd_pcm_substream *substream)
 	hw.buffer_bytes_max = SIZE_MAX;
 	hw.fifo_size = 16;
 	ret = snd_dmaengine_pcm_refine_runtime_hwparams(substream, &dma_data,
-							&hw, chan);
+							&hw, dcpaud->chan);
 	if (ret)
 		return ret;
 	substream->runtime->hw = hw;
 
-	return snd_dmaengine_pcm_open(substream, chan);
+	return snd_dmaengine_pcm_open(substream, dcpaud->chan);
 }
 
 static int dcp_pcm_close(struct snd_pcm_substream *substream)
@@ -444,10 +474,6 @@ static int dcpaud_create_pcm(struct dcp_audio *dcpaud)
 
 	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &dcp_playback_ops);
 	dcpaud->substream = pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].substream;
-	snd_pcm_set_managed_buffer(dcpaud->substream, SNDRV_DMA_TYPE_DEV_IRAM,
-				   dcpaud->chan->device->dev, 1024 * 1024,
-				   SIZE_MAX);
-
 	pcm->nonatomic = true;
 	pcm->private_data = dcpaud;
 	strscpy(pcm->name, card->shortname, sizeof(pcm->name));
@@ -496,26 +522,29 @@ static void dcpaud_set_card_names(struct dcp_audio *dcpaud)
 	strscpy(card->shortname, "Apple DisplayPort", sizeof(card->shortname));
 }
 
+#ifdef CONFIG_SND_DEBUG
+static void dcpaud_expose_debugfs_blob(struct dcp_audio *dcpaud, const char *name, void *base, size_t size)
+{
+	struct debugfs_blob_wrapper *wrapper;
+	wrapper = devm_kzalloc(dcpaud->dev, sizeof(*wrapper), GFP_KERNEL);
+	if (!wrapper)
+		return;
+	wrapper->data = base;
+	wrapper->size = size;
+	debugfs_create_blob(name, 0600, dcpaud->card->debugfs_root, wrapper);
+}
+#else
+static void dcpaud_expose_debugfs_blob(struct dcp_audio *dcpaud, const char *name, void *base, size_t size) {}
+#endif
+
 extern bool hdmi_audio;
 
 static int dcpaud_init_snd_card(struct dcp_audio *dcpaud)
 {
 	int ret;
-	struct dma_chan *chan;
-
 	if (!hdmi_audio)
 		return -ENODEV;
 
-	chan = of_dma_request_slave_channel(dcpaud->dev->of_node, "tx");
-	/* squelch dma channel request errors, the driver will try again alter */
-	if (!chan) {
-		dev_warn(dcpaud->dev, "audio TX DMA channel request failed\n");
-		return 0;
-	} else if (IS_ERR(chan)) {
-		dev_warn(dcpaud->dev, "audio TX DMA channel request failed: %pE\n", chan);
-		return 0;
-	}
-	dcpaud->chan = chan;
 
 	ret = snd_card_new(dcpaud->dev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1,
 			   THIS_MODULE, 0, &dcpaud->card);
@@ -548,35 +577,12 @@ static int dcpaud_init_snd_card(struct dcp_audio *dcpaud)
 	return ret;
 }
 
-#ifdef CONFIG_SND_DEBUG
-static void dcpaud_expose_debugfs_blob(struct dcp_audio *dcpaud, const char *name, void *base, size_t size)
-{
-	struct debugfs_blob_wrapper *wrapper;
-	wrapper = devm_kzalloc(dcpaud->dev, sizeof(*wrapper), GFP_KERNEL);
-	if (!wrapper)
-		return;
-	wrapper->data = base;
-	wrapper->size = size;
-	debugfs_create_blob(name, 0600, dcpaud->card->debugfs_root, wrapper);
-}
-#else
-static void dcpaud_expose_debugfs_blob(struct dcp_audio *dcpaud, const char *name, void *base, size_t size) {}
-#endif
-
 void dcpaud_connect(struct platform_device *pdev, bool connected)
 {
 	struct dcp_audio *dcpaud = platform_get_drvdata(pdev);
 
 	mutex_lock(&dcpaud->data_lock);
 
-	if (!dcpaud->chan) {
-		int ret = dcpaud_init_snd_card(dcpaud);
-		if (ret) {
-			dcpaud->dcp_connected = connected;
-			mutex_unlock(&dcpaud->data_lock);
-			return;
-		}
-	}
 	dcpaud_report_hotplug(dcpaud, connected);
 }
 
@@ -643,14 +649,17 @@ static int dcpaud_comp_bind(struct device *dev, struct device *main, void *data)
 	dcpaud->dma_link = device_link_add(dev, dcpaud->dma_dev, DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE |
 					   DL_FLAG_STATELESS);
 
-	mutex_lock(&dcpaud->data_lock);
 	/* ignore errors to prevent audio issues affecting the display side */
-	dcpaud_init_snd_card(dcpaud);
-	mutex_unlock(&dcpaud->data_lock);
+	ret = dcpaud_init_snd_card(dcpaud);
 
-	ret = device_create_file(dev, &dev_attr_probe_snd_card);
-        if (ret)
-		dev_info(dev, "creating force probe sysfs file failed: %d\n", ret);
+	if (!ret) {
+		dcpaud_expose_debugfs_blob(dcpaud, "selected_cookie", &dcpaud->selected_cookie,
+					sizeof(dcpaud->selected_cookie));
+		dcpaud_expose_debugfs_blob(dcpaud, "elements", dcpaud->elements,
+					DCPAUD_ELEMENTS_MAXSIZE);
+		dcpaud_expose_debugfs_blob(dcpaud, "product_attrs", dcpaud->productattrs,
+					DCPAUD_PRODUCTATTRS_MAXSIZE);
+	}
 
 	return 0;
 }