External HDMI receivers have analog circuitry that needs to be powered-on when exiting standby, and a mechanism to detect PCM v. IEC61937 data. These two steps take time and up to 2-3 seconds of audio may be muted when starting playback.

Intel hardware (Haswell and beyond) can keep the link active with a 'silent stream', so that the receiver does not go through those two steps when valid audio is transmitted. This mechanism relies on an setting the channel_id as 0xf, sending info packet and preventing the codec from going to D3, which will increase the platform static power consumption. The info packet assumes a basic 2ch stereo, and the silent stream is enabled when connecting a monitor. In case of format changes the detection of PCM v. IEC61937 needs to be re-run. In this case there is no way to avoid the 2-3s mute.

The silent stream is enabled with a Kconfig option, as well as a kernel parameter should there be a need to override the build time default. This approach is used based on the power_save capability as an example, but in the future, it may be used with a kcontrol, depending on UCM support for HDaudio legacy.

Signed-off-by: Harsha Priya harshapriya.n@intel.com Signed-off-by: Emmanuel Jillela emmanuel.jillela@intel.com Reviewed-by: Kai Vehmanen kai.vehmanen@linux.intel.com Reported-by: kernel test robot lkp@intel.com --- Change History:

v3: - Removed eld_valid check along side of silent stream enable check as its redundant with the monitor_present variable - Limited the change to take affect only for Haswell and beyond Intel platforms - As per the spec, setting the channel_id as 0xf before sending info packet - Fixed issue reported by Kernel Test Robot (tag added) - Tested on Intel Cometlake based Chromebook connected to few different monitors and docks.

v2: - Kconfig symbol depends on SND_HDA_INTEL. - Added valid eld check to along side of silent stream enable check, under which silent stream is enabled. - Error prints added for codec power up, power down functions. - The silent stream is enabled with a Kconfig/module parameter following the power_save capability as an example. But in the future, it may be used with a kcontrol, depending on UCM support for HDaudio legacy.

v1: - Initial version.

sound/pci/hda/Kconfig | 14 ++++++++++ sound/pci/hda/patch_hdmi.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 78 insertions(+)

diff --git a/sound/pci/hda/Kconfig b/sound/pci/hda/Kconfig index 3f9abda..bf213e5 100644 --- a/sound/pci/hda/Kconfig +++ b/sound/pci/hda/Kconfig @@ -239,6 +239,20 @@ config SND_HDA_POWER_SAVE_DEFAULT The default time-out value in seconds for HD-audio automatic power-save mode. 0 means to disable the power-save mode.

+config SND_HDA_INTEL_HDMI_SILENT_STREAM + bool "Enable Silent Stream always for HDMI" + depends on SND_HDA_INTEL + help + Intel hardware has a feature called 'silent stream', that + keeps external HDMI receiver's analog circuitry powered on + avoiding 2-3 sec silence during playback start. This mechanism + relies on setting channel_id as 0xf, sending info packet and + preventing codec D3 entry (increasing platform static power + consumption when HDMI receiver is plugged-in). 2-3 sec silence + at the playback start is expected whenever there is format change. + (default is 2 channel format). + Say Y to enable Silent Stream feature. + endif

endmenu diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c index e2b21ef..18eabcf 100644 --- a/sound/pci/hda/patch_hdmi.c +++ b/sound/pci/hda/patch_hdmi.c @@ -42,6 +42,11 @@ static bool enable_acomp = true; module_param(enable_acomp, bool, 0444); MODULE_PARM_DESC(enable_acomp, "Enable audio component binding (default=yes)");

+static bool enable_silent_stream = +IS_ENABLED(CONFIG_SND_HDA_INTEL_HDMI_SILENT_STREAM); +module_param(enable_silent_stream, bool, 0644); +MODULE_PARM_DESC(enable_silent_stream, "Enable Silent Stream for HDMI devices"); + struct hdmi_spec_per_cvt { hda_nid_t cvt_nid; int assigned; @@ -167,6 +172,7 @@ struct hdmi_spec { hda_nid_t vendor_nid; const int *port_map; int port_num; + bool send_silent_stream; /* Flag to enable silent stream feature */ };

#ifdef CONFIG_SND_HDA_COMPONENT @@ -1634,21 +1640,72 @@ static void hdmi_present_sense_via_verbs(struct hdmi_spec_per_pin *per_pin, snd_hda_power_down_pm(codec); }

+static void silent_stream_enable(struct hda_codec *codec, + struct hdmi_spec_per_pin *per_pin) +{ + unsigned int newval, oldval; + + codec_dbg(codec, "hdmi: enabling silent stream for NID %d\n", + per_pin->pin_nid); + + mutex_lock(&per_pin->lock); + + if (!per_pin->channels) + per_pin->channels = 2; + + oldval = snd_hda_codec_read(codec, per_pin->pin_nid, 0, + AC_VERB_GET_CONV, 0); + newval = (oldval & 0xF0) | 0xF; + snd_hda_codec_write(codec, per_pin->pin_nid, 0, + AC_VERB_SET_CHANNEL_STREAMID, newval); + + hdmi_setup_audio_infoframe(codec, per_pin, per_pin->non_pcm); + + mutex_unlock(&per_pin->lock); +} + /* update ELD and jack state via audio component */ static void sync_eld_via_acomp(struct hda_codec *codec, struct hdmi_spec_per_pin *per_pin) { struct hdmi_spec *spec = codec->spec; struct hdmi_eld *eld = &spec->temp_eld; + bool monitor_prev, monitor_next;

mutex_lock(&per_pin->lock); eld->monitor_present = false; + monitor_prev = per_pin->sink_eld.monitor_present; eld->eld_size = snd_hdac_acomp_get_eld(&codec->core, per_pin->pin_nid, per_pin->dev_id, &eld->monitor_present, eld->eld_buffer, ELD_MAX_SIZE); eld->eld_valid = (eld->eld_size > 0); update_eld(codec, per_pin, eld, 0); + monitor_next = per_pin->sink_eld.monitor_present; mutex_unlock(&per_pin->lock); + + /* + * Power-up will call hdmi_present_sense, so the PM calls + * have to be done without mutex held. + */ + + if (spec->send_silent_stream) { + int pm_ret; + + if (!monitor_prev && monitor_next) { + pm_ret = snd_hda_power_up_pm(codec); + if (pm_ret < 0) + codec_err(codec, + "Monitor plugged-in, Failed to power up codec ret=[%d]\n", + pm_ret); + silent_stream_enable(codec, per_pin); + } else if (monitor_prev && !monitor_next) { + pm_ret = snd_hda_power_down_pm(codec); + if (pm_ret < 0) + codec_err(codec, + "Monitor plugged-out, Failed to power down codec ret=[%d]\n", + pm_ret); + } + } }

static void hdmi_present_sense(struct hdmi_spec_per_pin *per_pin, int repoll) @@ -2791,6 +2848,13 @@ static int intel_hsw_common_init(struct hda_codec *codec, hda_nid_t vendor_nid, spec->ops.setup_stream = i915_hsw_setup_stream; spec->ops.pin_cvt_fixup = i915_pin_cvt_fixup;

+ /* + * Enable silent stream feature, if it is enabled via + * module param or Kconfig option + */ + if (enable_silent_stream) + spec->send_silent_stream = true; + return parse_intel_hdmi(codec); }