drm: apple: audio: Avoid probe errors

Now that the DP audio driver is a component of the display sub-system
probe errors will bring down the whole display initialization.
To prevent that the audio driver must not fail. Allow delayed sound card
initialization if the DMA controller is not ready, for example because
the apple-sio module is missing (at all or just in the initeramfs).
In the case apple-sio is available later provide as sysfs file
"probe_snd_card" to trigger initialization.

Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

drivers/gpu/drm/apple/audio.c

@@ -42,6 +42,7 @@ struct dcp_audio {
 	unsigned int open_cookie;
 
 	struct mutex data_lock;
+	bool dcp_connected; /// dcp status keep for delayed initialization
 	bool connected;
 	unsigned int connection_cookie;
 
@@ -428,19 +429,8 @@ static int dcpaud_create_pcm(struct dcp_audio *dcpaud)
 {
 	struct snd_card *card = dcpaud->card;
 	struct snd_pcm *pcm;
-	struct dma_chan *chan;
 	int ret;
 
-	chan = of_dma_request_slave_channel(dcpaud->dev->of_node, "tx");
-	if (IS_ERR_OR_NULL(chan)) {
-		if (!chan)
-			return -EINVAL;
-
-		dev_err(dcpaud->dev, "can't request audio TX DMA channel: %pE\n", chan);
-		return PTR_ERR(chan);
-	}
-	dcpaud->chan = chan;
-
 #define NUM_PLAYBACK 1
 #define NUM_CAPTURE 0
 
@@ -451,7 +441,7 @@ 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,
-				   chan->device->dev, 1024 * 1024,
+				   dcpaud->chan->device->dev, 1024 * 1024,
 				   SIZE_MAX);
 
 	pcm->nonatomic = true;
@@ -461,12 +451,12 @@ static int dcpaud_create_pcm(struct dcp_audio *dcpaud)
 	return 0;
 }
 
+/* expects to be called with data_lock locked and unlocks it */
 static void dcpaud_report_hotplug(struct dcp_audio *dcpaud, bool connected)
 {
 	struct snd_pcm_substream *substream = dcpaud->substream;
 
-	mutex_lock(&dcpaud->data_lock);
-	if (dcpaud->connected == connected) {
+	if (!dcpaud->card || dcpaud->connected == connected) {
 		mutex_unlock(&dcpaud->data_lock);
 		return;
 	}
@@ -502,6 +492,53 @@ static void dcpaud_set_card_names(struct dcp_audio *dcpaud)
 	strcpy(card->shortname, "Apple DisplayPort");
 }
 
+static int dcpaud_init_snd_card(struct dcp_audio *dcpaud)
+{
+	int ret;
+	struct dma_chan *chan;
+
+	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);
+	if (ret)
+		return ret;
+
+	dcpaud_set_card_names(dcpaud);
+
+	ret = dcpaud_create_pcm(dcpaud);
+	if (ret)
+		goto err_free_card;
+
+	ret = dcpaud_create_chmap_ctl(dcpaud);
+	if (ret)
+		goto err_free_card;
+
+	ret = dcpaud_create_jack(dcpaud);
+	if (ret)
+		goto err_free_card;
+
+	ret = snd_card_register(dcpaud->card);
+	if (ret)
+		goto err_free_card;
+
+	return 0;
+err_free_card:
+	dev_warn(dcpaud->dev, "Failed to initialize sound card: %d\n", ret);
+	snd_card_free(dcpaud->card);
+	dcpaud->card = NULL;
+	return ret;
+}
+
 #ifdef CONFIG_SND_DEBUG
 static void dcpaud_expose_debugfs_blob(struct dcp_audio *dcpaud, const char *name, void *base, size_t size)
 {
@@ -520,15 +557,59 @@ static void dcpaud_expose_debugfs_blob(struct dcp_audio *dcpaud, const char *nam
 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);
 }
 
 void dcpaud_disconnect(struct platform_device *pdev)
 {
 	struct dcp_audio *dcpaud = platform_get_drvdata(pdev);
+
+	mutex_lock(&dcpaud->data_lock);
+
+	dcpaud->dcp_connected = false;
 	dcpaud_report_hotplug(dcpaud, false);
 }
 
+static ssize_t probe_snd_card_store(struct device *dev,
+				    struct device_attribute *attr,
+				    const char *buf, size_t count)
+{
+	int ret;
+	bool connected = false;
+	struct dcp_audio *dcpaud = dev_get_drvdata(dev);
+
+	mutex_lock(&dcpaud->data_lock);
+
+	if (!dcpaud->chan) {
+		ret = dcpaud_init_snd_card(dcpaud);
+		if (ret)
+			goto out_unlock;
+
+		connected = dcpaud->dcp_connected;
+		if (connected) {
+			dcpaud_report_hotplug(dcpaud, connected);
+			goto out;
+		}
+	}
+out_unlock:
+	mutex_unlock(&dcpaud->data_lock);
+out:
+	return count;
+}
+
+static const DEVICE_ATTR_WO(probe_snd_card);
+
 static int dcpaud_comp_bind(struct device *dev, struct device *main, void *data)
 {
 	struct dcp_audio *dcpaud = dev_get_drvdata(dev);
@@ -551,46 +632,28 @@ static int dcpaud_comp_bind(struct device *dev, struct device *main, void *data)
 	dcp_pdev = of_find_device_by_node(dcp_node);
 	of_node_put(dcp_node);
 	if (!dcp_pdev) {
-		dev_info(dev, "No DP/HDMI audio device not ready\n");
+		dev_info(dev, "No DP/HDMI audio device, dcp not ready\n");
 		return 0;
 	}
 	dcpaud->dcp_dev = &dcp_pdev->dev;
 
-	ret = snd_card_new(dev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1,
-			   THIS_MODULE, 0, &dcpaud->card);
-	if (ret)
-		return ret;
-
-	dcpaud_set_card_names(dcpaud);
-
-	ret = dcpaud_create_pcm(dcpaud);
-	if (ret)
-		goto err_free_card;
-
-	ret = dcpaud_create_chmap_ctl(dcpaud);
-	if (ret)
-		goto err_free_card;
-
-	ret = dcpaud_create_jack(dcpaud);
-	if (ret)
-		goto err_free_card;
-
-	ret = snd_card_register(dcpaud->card);
-	if (ret)
-		goto err_free_card;
-
 	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;
+	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);
 
-err_free_card:
-	snd_card_free(dcpaud->card);
-	return ret;
+	ret = device_create_file(dev, &dev_attr_probe_snd_card);
+        if (ret)
+		dev_info(dev, "creating force probe sysfs file failed: %d\n", ret);
+
+	return 0;
 }
 
 static void dcpaud_comp_unbind(struct device *dev, struct device *main,