Re: [PATCH] ALSA: hda - program ICT bits to support HBR audio

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 9/19/17 3:10 PM, Takashi Iwai wrote:
> On Tue, 19 Sep 2017 17:00:01 +0200,
> Subhransu S. Prusty wrote:
>>
>> From: Sriram Periyasamy <sriramx.periyasamy@intel.com>
>>
>> On recent Intel platforms (Haswell, Broadwell, Skylake, ApolloLake,
>> KabyLake, ...), the IEC Coding Type (ICT) bitfield in the Digital
>> Converter Control #3 needs to be set explicitly for HDMI/DisplayPort
>> High Bit Rate (HBR) audio playback to work. This was not required in
>> earlier platforms when HBR was first introduced. The ICT bits are
>> defined in Section 7.3.3.9 of the HDaudio 1.0a specification.
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98797
>>
>> Signed-off-by: Sriram Periyasamy <sriramx.periyasamy@intel.com>
>> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
>> Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@intel.com>
>> ---
>>   include/sound/hda_verbs.h  |  1 +
>>   sound/pci/hda/patch_hdmi.c | 18 ++++++++++++++++++
>>   2 files changed, 19 insertions(+)
>>
>> diff --git a/include/sound/hda_verbs.h b/include/sound/hda_verbs.h
>> index d0509db6d0ec..d2004d7feb2b 100644
>> --- a/include/sound/hda_verbs.h
>> +++ b/include/sound/hda_verbs.h
>> @@ -54,6 +54,7 @@ enum {
>>   #define AC_VERB_GET_EAPD_BTLENABLE		0x0f0c
>>   #define AC_VERB_GET_DIGI_CONVERT_1		0x0f0d
>>   #define AC_VERB_GET_DIGI_CONVERT_2		0x0f0e /* unused */
>> +#define AC_VERB_SET_DIGI_CONVERT_3		0x73e
> 
> The SET verb should be placed in the dedicated section instead.
> 
> 
>>   #define AC_VERB_GET_VOLUME_KNOB_CONTROL		0x0f0f
>>   /* f10-f1a: GPIO */
>>   #define AC_VERB_GET_GPIO_DATA			0x0f15
>> diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
>> index 53f9311370de..2dcd99d2a757 100644
>> --- a/sound/pci/hda/patch_hdmi.c
>> +++ b/sound/pci/hda/patch_hdmi.c
>> @@ -906,6 +906,7 @@ static int hdmi_setup_stream(struct hda_codec *codec, hda_nid_t cvt_nid,
>>   			      hda_nid_t pin_nid, u32 stream_tag, int format)
>>   {
>>   	struct hdmi_spec *spec = codec->spec;
>> +	unsigned int param;
>>   	int err;
>>   
>>   	err = spec->ops.pin_hbr_setup(codec, pin_nid, is_hbr_format(format));
>> @@ -915,6 +916,23 @@ static int hdmi_setup_stream(struct hda_codec *codec, hda_nid_t cvt_nid,
>>   		return err;
>>   	}
>>   
>> +	/*
>> +	 * on recent platforms IEC Coding Type is required for HBR support,
>> +	 * read current Digital Converter settings and set ICT bitfield if
>> +	 * needed.
>> +	 */
>> +	param = snd_hda_codec_read(codec, cvt_nid, 0,
>> +				AC_VERB_GET_DIGI_CONVERT_1, 0);
>> +
>> +	param = (param >> 16) & ~(AC_DIG3_ICT);
>> +
>> +	/* on recent platforms ICT mode is required for HBR support */
>> +	if (is_hbr_format(format))
>> +		param |= 0x1;
>> +
>> +	snd_hda_codec_write(codec, cvt_nid, 0,
>> +				AC_VERB_SET_DIGI_CONVERT_3, param);
> 
> Do all codecs support this verb?  I'm a bit worried, since this
> function gets called for all codecs, and some of them must be fairly
> old.

My favorite hobby: forensic software engineering...

This converter contains both the ICT (IEC coding type) and KAE (Keep 
Alive Enable).
The HDaudio 1.0 spec dated (April 15, 2004) makes no reference to any of 
those bits - even if it lists HDMI as a supported output (HDMI 1.0 was 
released in 2002).

HDMI 1.3 added support for HDMI HBR and was released on June 22, 2006,

The first DCN I see with those bits is from June 6, 2009
https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/high-definition-audio-low-power.pdf
KAE became mandatory after July 1st, 2011.

So yes in theory there is a risk that on a platform produced between 
2004 and 2009 (maybe 2011) accessing this verb might generate an error 
or an warning. I don't know the standard and implementation enough to 
know if this can be queried and what happens when accessing undefined 
verbs. The oldest working machine I have is from 2010, older stuff was 
scrapped/recycled.

I guess we could set a capability and set it for newer platforms making 
use of intel_hsw_common_init() in patch_hdmi.c (we already use the codec 
ID to match the relevant quirks). We could also check on Baytrail if 
it's needed with a Minnowboard.