I applied the patch and when connecting the Denon MC7000 the attached is 
what dmesg shows...
Hope you can find something useful in there.

Please let me know, if I can be of any more help.

Thanks a lot.
Tobias


Am 16.01.20 um 14:47 schrieb Takashi Iwai:
> On Thu, 16 Jan 2020 12:58:00 +0100,
> Tobias wrote:
>> Thank you for taking care of this...
>>
>> I have tried with the latest Kernel 5.4.11 in Ubuntu 16.04 and
>> $ dmesg
>> still shows
>> "clock source 65 is not valid, cannot use"
>>
>> My current running stable system is
>>
>> $ uname -a
>> $ Linux tobias-V130 4.15.0-23-generic #25~16.04.1 SMP Fri Dec 20
>> 20:16:19 CET 2019 x86_64 x86_64 x86_64 GNU/Linux
>>
>> in where I applied the chane described in here:
>> https://alsa-user.narkive.com/2tDAO87f/troubleshooting-new-usb-audio-device#post11
>>
>> Just for my understanding what you now need me to do...
>> deleting the line in /sound/usb/clock.c that states "return -ENXIO;"
>> and compile the kernel again.
> Yes, and with that, the error message still remains.  That's not
> wrong.  The question is to identify who calls this function.
> So...
>
>> Clemes mentioned in his last post to add logging but I have no idea
>> what he means by that. Can you briefly guide me what I would need to
>> do?
> ... try the patch below instead.  This should work for the recent
> kernels.  It'll give Oops-like kernel WARNING with stack traces, so
> show them.  There can be multiple occurrences.
>
>
> Takashi
>
> diff --git a/sound/usb/clock.c b/sound/usb/clock.c
> index 018b1ecb5404..8d92a946f978 100644
> --- a/sound/usb/clock.c
> +++ b/sound/usb/clock.c
> @@ -219,10 +219,10 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip, int entity_id,
>   		entity_id = source->bClockID;
>   		if (validate && !uac_clock_source_is_valid(chip, UAC_VERSION_2,
>   								entity_id)) {
> -			usb_audio_err(chip,
> +			WARN(1,
>   				"clock source %d is not valid, cannot use\n",
>   				entity_id);
> -			return -ENXIO;
> +			/* return -ENXIO; */
>   		}
>   		return entity_id;
>   	}