[alsa-devel] [PATCH 4/4] ALSA: x86: Enable keep-link feature

[Takashi Iwai]

This patch enables the "keep-link" feature experimentally.  It's a
feature where the device keeps the link and sending the silent output
even after the PCM device is closed.  Then the receiver will be
resumed quickly once when a PCM is opened and a stream is sent again.

The stream link is turned off when the device goes to the auto
suspend, and it's set to two seconds after the PCM close.  This
timeout value can be changed dynamically in a standard way via sysfs
like other drivers.  For example, to make it 10 seconds, run like:

  echo 10000 > /sys/bus/platform/devices/hdmi-lpe-audio/power/autosuspend_delay_ms

This new keep-link feature itself is controlled via a new module
option, keep_link.  You can turn it on/off, again, via sysfs like:

  echo 0 > /sys/module/snd_hdmi_lpe_audio/parameters/keep_link

As default, the feature is turned on.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/x86/intel_hdmi_audio.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/sound/x86/intel_hdmi_audio.c b/sound/x86/intel_hdmi_audio.c
index 95b07a260d54..506cff306b5c 100644
--- a/sound/x86/intel_hdmi_audio.c
+++ b/sound/x86/intel_hdmi_audio.c
@@ -52,6 +52,10 @@ module_param_named(id, hdmi_card_id, charp, 0444);
 MODULE_PARM_DESC(id,
 		"ID string for INTEL Intel HDMI Audio controller.");
 
+static bool keep_link = true;
+module_param(keep_link, bool, 0644);
+MODULE_PARM_DESC(keep_link, "Keep link on after the stream is closed.");
+
 /*
  * ELD SA bits in the CEA Speaker Allocation data block
  */
@@ -217,8 +221,12 @@ static void had_write_register(struct snd_intelhad *ctx, u32 reg, u32 val)
 static void had_enable_audio(struct snd_intelhad *intelhaddata,
 			     bool enable)
 {
+	if (intelhaddata->aud_config.regx.aud_en == enable)
+		return;
+
 	/* update the cached value */
 	intelhaddata->aud_config.regx.aud_en = enable;
+	intelhaddata->aud_config.regx.underrun = keep_link;
 	had_write_register(intelhaddata, AUD_CONFIG,
 			   intelhaddata->aud_config.regval);
 }
@@ -901,6 +909,21 @@ static void had_init_ringbuf(struct snd_pcm_substream *substream,
 	intelhaddata->bd_head = 0; /* reset at head again before starting */
 }
 
+/* Set up the silent output after PCM close */
+static void had_keep_silent(struct snd_intelhad *intelhaddata)
+{
+	int i;
+
+	if (!(keep_link && intelhaddata->connected &&
+	      intelhaddata->aud_config.regval))
+		return;
+
+	for (i = 0; i < HAD_NUM_OF_RING_BUFS; i++)
+		had_invalidate_bd(intelhaddata, i);
+	intelhaddata->need_reset = true; /* reset at next */
+	had_enable_audio(intelhaddata, true);
+}
+
 /* process a bd, advance to the next */
 static void had_advance_ringbuf(struct snd_pcm_substream *substream,
 				struct snd_intelhad *intelhaddata)
@@ -1007,6 +1030,9 @@ static void had_do_reset(struct snd_intelhad *intelhaddata)
 	if (!intelhaddata->need_reset)
 		return;
 
+	/* disable the silent output */
+	had_enable_audio(intelhaddata, false);
+
 	/* Reset buffer pointers */
 	had_reset_audio(intelhaddata);
 	wait_clear_underrun_bit(intelhaddata);
@@ -1101,6 +1127,8 @@ static int had_pcm_close(struct snd_pcm_substream *substream)
 	}
 	spin_unlock_irq(&intelhaddata->had_spinlock);
 
+	had_keep_silent(intelhaddata);
+
 	pm_runtime_mark_last_busy(intelhaddata->dev);
 	pm_runtime_put_autosuspend(intelhaddata->dev);
 	return 0;
@@ -1626,6 +1654,9 @@ static int hdmi_lpe_audio_runtime_suspend(struct device *dev)
 		had_substream_put(ctx);
 	}
 
+	/* disable the silent output */
+	had_enable_audio(ctx, false);
+
 	return 0;
 }
 
@@ -1642,6 +1673,9 @@ static int __maybe_unused hdmi_lpe_audio_suspend(struct device *dev)
 
 static int hdmi_lpe_audio_runtime_resume(struct device *dev)
 {
+	struct snd_intelhad *ctx = dev_get_drvdata(dev);
+
+	had_keep_silent(ctx);
 	pm_runtime_mark_last_busy(dev);
 	return 0;
 }
@@ -1799,6 +1833,10 @@ static int hdmi_lpe_audio_probe(struct platform_device *pdev)
 	pdata->notify_pending = false;
 	spin_unlock_irq(&pdata->lpe_audio_slock);
 
+	/* set a relatively long autosuspend delay (2 seconds) for making
+	 * keep_link feature working reasonably
+	 */
+	pm_runtime_set_autosuspend_delay(&pdev->dev, 2000);
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_mark_last_busy(&pdev->dev);
 
-- 
2.11.1