I tried to convey in code what I had in mind.
It's a rough sketch and very much untested.
--- clock.5.14-rc2.c 2021-07-24 18:30:09.773718208 -0000
+++ clock-one-to-one.c 2021-07-24 18:35:52.276412366 -0000
@@ -54,6 +54,61 @@ static void *find_uac_clock_desc(struct
return NULL;
}
+/* Behringer UFX1604 / UFX1204 have a simple one-to-one
+ * topology where there is only one Clock Selector, only
+ * one Clock Source linked to USB SOF and no Clock Multipliers.
+ *
+ * This function checks for the presence of such a
+ * one-to-one clock selector / clock source topology
+ * so that it's possible to safely set the one and only
+ * Clock Selector to the one and only Clock Source
+ * upon sample rate change without breaking devices
+ * with more complicated topologies.
+ */
+
+static bool one_to_one_clock_topology(struct usb_host_interface
*iface, int proto)
+{
+ int clock_sources, clock_selectors, clock_multipliers = 0;
+ int source_version, selector_version, multiplier_version;
+ int found_count;
+
+ void *cs = NULL;
+
+ if (proto == UAC_VERSION_3) {
+ source_version = UAC3_CLOCK_SOURCE;
+ selector_version = UAC3_CLOCK_SELECTOR;
+ multiplier_version = UAC3_CLOCK_MULTIPLIER;
+ }
+
+ else {
+ source_version = UAC2_CLOCK_SOURCE;
+ selector_version = UAC2_CLOCK_SELECTOR;
+ multiplier_version = UAC2_CLOCK_MULTIPLIER;
+ }
+
+ if ((found_count = snd_usb_count_csint_desc(iface->extra,
iface->extralen,
+ cs, source_version)) > 0) {
+ clock_sources = found_count;
+ }
+
+ if ((found_count = snd_usb_count_csint_desc(iface->extra,
iface->extralen,
+ cs, selector_version)) > 0) {
+ clock_selectors = found_count;
+ }
+
+ if ((found_count = snd_usb_count_csint_desc(iface->extra,
iface->extralen,
+ cs, multiplier_version)) > 0) {
+ clock_multipliers = found_count;
+ }
+
+ if ((clock_sources == 1) && (clock_selectors == 1) &&
(clock_multipliers == 0)) {
+ return true;
+ }
+
+ return false;
+}
+
+
static bool validate_clock_source(void *p, int id, int proto)
{
union uac23_clock_source_desc *cs = p;
@@ -323,7 +378,7 @@ static int __uac_clock_find_source(struc
ret = __uac_clock_find_source(chip, fmt,
sources[ret - 1],
visited, validate);
- if (ret > 0) {
+ if (ret > 0 &&
one_to_one_clock_topology(chip->ctrl_intf, proto)) {
err = uac_clock_selector_set_val(chip, entity_id, cur);
if (err < 0)
return err;
--- helper.5.14-rc2.c 2021-07-24 18:30:25.042526253 -0000
+++ helper-one-to-one.c 2021-07-24 18:35:45.019503597 -0000
@@ -64,6 +64,29 @@ void *snd_usb_find_csint_desc(void *buff
}
/*
+ * find every class-specified interface descriptor with the given subtype
+ * and return how many did it find
+ */
+int snd_usb_count_csint_desc(void *buffer, int buflen, void *after,
u8 dsubtype)
+{
+ int count = 0;
+ unsigned char *p = after;
+
+ while ((p = snd_usb_find_desc(buffer, buflen, p,
+ USB_DT_CS_INTERFACE)) != NULL) {
+ if (p[0] >= 3 && p[2] == dsubtype)
+ count++;
+ }
+
+ if (count > 0) {
+ return count;
+ }
+
+ return 0;
+}
+
+
+/*
* Wrapper for usb_control_msg().
* Allocates a temp buffer to prevent dmaing from/to the stack.
*/
--- helper.5.14-rc2.h 2021-07-24 18:30:35.219398312 -0000
+++ helper-one-to-one.h 2021-07-24 18:29:34.139166195 -0000
@@ -7,6 +7,8 @@ unsigned int snd_usb_combine_bytes(unsig
void *snd_usb_find_desc(void *descstart, int desclen, void *after, u8 dtype);
void *snd_usb_find_csint_desc(void *descstart, int desclen, void
*after, u8 dsubtype);
+int snd_usb_count_csint_desc(void *descstart, int desclen, void
*after, u8 dsubtype);
+
int snd_usb_ctl_msg(struct usb_device *dev, unsigned int pipe,
__u8 request, __u8 requesttype, __u16 value, __u16 index,
void *data, __u16 size);
On Sat, Jul 24, 2021 at 3:20 PM Geraldo Nascimento
<geraldogabriel@xxxxxxxxx> wrote:
>
> > Dr. Iwai, perhaps we could restrict the generalized fix for the
> > Behringer UFX1604 / UFX1204 with some simple logic to devices that
> > only have *one* clock source.
>
> Okay, rereading the original commit log from Cihhao Chen I gather
> Samsung USBC Headset (AKG) with VID/PID (0x04e8/0xa051) actually has
> two clock selectors and only one clock source.
>
> Correct me if I'm wrong.
>
> This is complicated by the fact I haven't been able to find a lsusb -v
> of Samsung USBC Headset (AKG) with VID/PID (0x04e8/0xa051)
>
> Even so, my proposition still stands: devices with only one clock
> source and only one clock selector should be able to handle us
> selecting the clock selector to the only clock source.
