Re: [PATCH] ALSA: usb-audio: fix incorrect clock source setting

On Mon, Jul 26, 2021 at 8:42 AM chihhao chen [off-list ref] wrote:

Hello,

Attach USB descriptor of clock source and selectior for this earphone.

AC Clock Source Descriptor:
------------------------------

Value   Valuename
0x08    bLength
0x24    bDescriptorType
0x0A    bDescriptorSubtype
0x09    bClockID
0x03    bmAttributes
0x07    bmControls
0x00    bAssocTerminal
0x00    iClockSource
Hex dump:
0x08 0x24 0x0A 0x09 0x03 0x07 0x00 0x00

AC Clock Selector Descriptor:
------------------------------

Value   Valuename
0x09    bLength
0x24    bDescriptorType
0x0B    bDescriptorSubtype
0x0B    bClockID
0x02    bNrInPins
0x09    baCSourceID(1)
0x0A    baCSourceID(2)
0x03    bmControls
0x00    iClockSelector
Hex dump:
0x09 0x24 0x0B 0x0B 0x02 0x09 0x0A 0x03 0x00

AC Clock Source Descriptor:
------------------------------

Value   Valuename
0x08    bLength
0x24    bDescriptorType
0x0A    bDescriptorSubtype
0x0A    bClockID
0x03    bmAttributes
0x07    bmControls
0x00    bAssocTerminal
0x00    iClockSource
Hex dump:
0x08 0x24 0x0A 0x0A 0x03 0x07 0x00 0x00

AC Clock Selector Descriptor:
------------------------------

Value   Valuename
0x09    bLength
0x24    bDescriptorType
0x0B    bDescriptorSubtype
0x0C    bClockID
0x02    bNrInPins
0x09    baCSourceID(1)
0x0A    baCSourceID(2)
0x03    bmControls
0x00    iClockSelector
Hex dump:
0x09 0x24 0x0B 0x0C 0x02 0x09 0x0A 0x03 0x00

Thanks
Chihhao

Thank you, Chihhao.

So I was wrong about Samsung USBC Headset (AKG) with VID/PID
(0x04e8/0xa051) having a Clock Multiplier.

There are two Clock Sources, both linked to the USB SOF with fixed sample rate.

Plus two Clock Selectors which are host-programmable and can be set to
either of the two Clock Sources.


I'm still at a loss to explain what is going wrong here.

Would a printk() reveal the first explicit
uac_clock_selector_set_val() on the Clock Selector associated with
USB_IN sets Clock Source ID to pin 1 with Clock Source ID 0x9?

Or is it the other way around, i.e. it sets the Clock Source ID to pin
2 with Clock ID 0xA for the capture stream Clock Selector?


Chihhao Chen, could you please try the following patch for debugging
purposes and share what is printed in dmesg?

Please try one time with your fix applied and one time without, i.e.
with an otherwise unmodified vanilla kernel.

Thank you,
Geraldo Nascimento

--- clock.c.orig    2021-07-17 12:15:06.416028360 -0000
+++ clock.c    2021-07-26 20:45:58.713881962 -0000

@@ -300,6 +300,7 @@ static int __uac_clock_find_source(struc
         /* the entity ID we are looking for is a selector.
          * find out what it currently selects */
         ret = uac_clock_selector_get_val(chip, clock_id);
+        printk(KERN_ERR "FOR EP %x: Clock Selector %x has pin %d for

Clock Source ID %x selected\n", (unsigned int)fmt->endpoint, clock_id,
ret, sources[ret - 1]);
         if (ret < 0) {
             if (!chip->autoclock)
                 return ret;

@@ -324,6 +325,7 @@ static int __uac_clock_find_source(struc
                           sources[ret - 1],
                           visited, validate);
         if (ret > 0) {
+            printk(KERN_ERR "FOR EP %x: Found Source! Clock Selector

%x has pin %d for Clock Source ID %x about to be reselected\n",
(unsigned int)fmt->endpoint, entity_id, cur, sources[cur - 1]);
             err = uac_clock_selector_set_val(chip, entity_id, cur);
             if (err < 0)
                 return err;

@@ -344,6 +346,7 @@ static int __uac_clock_find_source(struc
             if (ret < 0)
                 continue;

+            printk(KERN_ERR "FOR EP %x: Found source by trial and

error! Clock Selector %x has pin %d for Clock Source ID %x about to be
selected\n", (unsigned int)fmt->endpoint, entity_id, i, sources[i -
1]);
             err = uac_clock_selector_set_val(chip, entity_id, i);
             if (err < 0)
                 continue;

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