Re: [alsa-devel] USB Audio Interface / Denon MC7000 and MC8000 controller

[Takashi Iwai <tiwai@suse.de>]

On Thu, 06 Feb 2020 23:09:33 +0100,
Alexander Tsoy wrote:
> 
> В Чт, 06/02/2020 в 11:06 +0100, Tobias пишет:
> > Thank you so much Alexander!
> > I used latest Kernel and patched as you suggested. The Device is
> > working 
> > now giving sound on all 4 channels, even though dmesg still shows
> > the 
> > error message as you can see here:
> > 
> > uname -a:
> > Linux tobias-V130 5.5.2 #1 SMP Thu Feb 6 09:41:57 CET 2020 x86_64
> > x86_64 
> > x86_64 GNU/Linux
> > 
> > dmesg:
> > [   62.918777] usb 1-1.3: new high-speed USB device number 6 using
> > xhci_hcd
> > [   62.939293] usb 1-1.3: New USB device found, idVendor=15e4, 
> > idProduct=8004, bcdDevice=11.10
> > [   62.939295] usb 1-1.3: New USB device strings: Mfr=1, Product=2, 
> > SerialNumber=3
> > [   62.939297] usb 1-1.3: Product: DENON DJ MC7000
> > [   62.939298] usb 1-1.3: Manufacturer: DENON DJ
> > [   62.939299] usb 1-1.3: SerialNumber: 201603
> > [   62.942232] usb 1-1.3: clock source 65 is not valid, cannot use
> > [   62.943998] usb 1-1.3: clock source 65 is not valid, cannot use
> > [   63.013306] usb 1-1.3: clock source 65 is not valid, cannot use
> > [   63.028912] usb 1-1.3: clock source 65 is not valid, cannot use
> > [   63.029675] usb 1-1.3: clock source 65 is not valid, cannot use
> > [   63.037813] usb 1-1.3: clock source 65 is not valid, cannot use
> > [   63.063865] usb 1-1.3: clock source 65 is not valid, cannot use
> 
> Yes, this is expected.
> 
> > 
> > I checked in file /sound/usb/clock.c that within functions
> > 
> > static int __uac_clock_find_source
> > static int __uac3_clock_find_source
> > 
> > there is another check that possibly gives the warning.
> > 
> > Maybe the warning "cannot use" should not be displayed when a Denon 
> > Audio device is attached as it is misleading.
> 
> Please try the patch below. I've dropped UAC3 support and changed
> __uac_clock_find_source() and __uac3_clock_find_source() to print
> errors only in debug mode, as we make the final decision about clock
> validity in set_sample_rate_v2v3().
> 
> 
> Dear Takashi, what do you think about this approach. Is it acceptable?

Yes, the approach looks good to me.
Just a few comments:

> diff --git a/sound/usb/clock.c b/sound/usb/clock.c
> index 018b1ecb5404..e978b46efc85 100644
> --- a/sound/usb/clock.c
> +++ b/sound/usb/clock.c
> @@ -197,6 +197,32 @@ static bool uac_clock_source_is_valid(struct snd_usb_audio *chip,
>  	return data ? true :  false;
>  }
>  
> +/*
> + * Assume the clock is valid if clock source supports only one single sample
> + * rate, its type is not external and a terminal is connected directly to it
> + * (there is no clock selector). This is needed for some Denon DJ controllers,
> + * that always reports that clock is invalid.
> + */
> +static bool uac_clock_source_is_valid_quirk(struct snd_usb_audio *chip,
> +					    struct audioformat *fmt,
> +					    int clock)
> +{
> +	if (fmt->protocol == UAC_VERSION_2) {
> +		struct uac_clock_source_descriptor *cs_desc =
> +			snd_usb_find_clock_source(chip->ctrl_intf, clock);
> +
> +		if (!cs_desc)
> +			return false;
> +
> +		return (fmt->nr_rates == 1 &&
> +			(fmt->clock & 0xff) == cs_desc->bClockID &&
> +			(cs_desc->bmAttributes & 0x3) !=
> +				UAC_CLOCK_SOURCE_TYPE_EXT);
> +	}
> +
> +	return false;

IMO it's safer to call from the specific failure path, i.e. 

 static bool uac_clock_source_is_valid(....)
 {
	....
	err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC2_CS_CUR,
			      USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_IN,
			      UAC2_CS_CONTROL_CLOCK_VALID << 8,
			      snd_usb_ctrl_intf(chip) | (source_id << 8),
			      &data, sizeof(data));

	if (err < 0) {

		if (uac_clock_source_is_valid_quirk(....))
			return true;

		dev_warn(&dev->dev,
			 "%s(): cannot get clock validity for id %d\n",
			   __func__, source_id);
		return false;
	}

Then you can pass cs_desc there, too.


> +}
> +
>  static int __uac_clock_find_source(struct snd_usb_audio *chip, int entity_id,
>  				   unsigned long *visited, bool validate)
>  {
> @@ -219,7 +245,7 @@ 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,
> +			usb_audio_dbg(chip,
>  				"clock source %d is not valid, cannot use\n",
>  				entity_id);
>  			return -ENXIO;

Hm, it's not good to hide the error message always.  This is a common
error on many devices and suppressing it would look cleaner but also
hide what's the reason.  Maybe we can add nowarn bool flag for certain
code paths?


thanks,

Takashi
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