Re: [alsa-devel] [PATCH v1 3/5] ALSA: hda - Add DP-MST conn list support

[Nikhil Mahale <nmahale@nvidia.com>]

On 11/14/19 4:27 PM, Takashi Iwai wrote:
> On Thu, 14 Nov 2019 04:37:02 +0100,
> Nikhil Mahale wrote:
>>
>> Document change notification HDA040-A for the Intel High Definition
>> Audio 1.0a specification introduces a Device Select verb for Digital
>> Display Pin Widgets that are multi-stream capable. This verb selects
>> a Device Entry that is used by subsequent Pin Widget verbs,
>> including the Get Connection List Entry verb.
>>
>> This patch queries the current Device Select value, associates it
>> with the connection list, and updates the connection list management
>> code to consider dev_id along with nid.
> 
> I don't get why this is needed.  This is the list that is added only
> from snd_hda_override_conn_list(), and you don't change that call
> pattern, so dev_id is always zero.

In follow-on patch "ALSA: hda - Add DP-MST support for non-acomp codecs",
hdmi_read_pin_conn() calls into snd_hda_set_dev_select() before
running into code path -
  
  snd_hda_get_connections()
   |-> snd_hda_get_conn_list()
        |-> read_and_add_raw_conns()
             |-> snd_hda_override_conn_list()
                  |-> add_conn_list()

If I understand spec correctly, conn_list need to read/write/track
along with device entry set into AC_VERB_SET_DEVICE_SEL verb, right?
This patch address that limited part here.

Thanks,
Nikhil Mahale

> thanks,
> 
> Takashi
> 
>>
>> Signed-off-by: Nikhil Mahale <nmahale@nvidia.com>
>> Reviewed-by: Aaron Plattner <aplattner@nvidia.com>
>> ---
>>  sound/pci/hda/hda_codec.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c
>> index a2fb19129219..8f32cab8f4a4 100644
>> --- a/sound/pci/hda/hda_codec.c
>> +++ b/sound/pci/hda/hda_codec.c
>> @@ -88,6 +88,7 @@ struct hda_conn_list {
>>  	struct list_head list;
>>  	int len;
>>  	hda_nid_t nid;
>> +	int dev_id;
>>  	hda_nid_t conns[0];
>>  };
>>  
>> @@ -96,8 +97,9 @@ static struct hda_conn_list *
>>  lookup_conn_list(struct hda_codec *codec, hda_nid_t nid)
>>  {
>>  	struct hda_conn_list *p;
>> +	int dev_id = snd_hda_get_dev_select(codec, nid);
>>  	list_for_each_entry(p, &codec->conn_list, list) {
>> -		if (p->nid == nid)
>> +		if (p->nid == nid && p->dev_id == dev_id)
>>  			return p;
>>  	}
>>  	return NULL;
>> @@ -113,6 +115,7 @@ static int add_conn_list(struct hda_codec *codec, hda_nid_t nid, int len,
>>  		return -ENOMEM;
>>  	p->len = len;
>>  	p->nid = nid;
>> +	p->dev_id = snd_hda_get_dev_select(codec, nid);
>>  	memcpy(p->conns, list, len * sizeof(hda_nid_t));
>>  	list_add(&p->list, &codec->conn_list);
>>  	return 0;
>> -- 
>> 2.16.4
>>

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