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ALSA: usb-audio: Add retry on -EPROTO from usb_set_interface()

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During initialisation of Focusrite USB audio interfaces, -EPROTO is
sometimes returned from usb_set_interface(), which sometimes prevents
the device from working: subsequent usb_set_interface() and
uac_clock_source_is_valid() calls fail.

This patch adds up to 5 retries in endpoint_set_interface(), with a
delay starting at 5ms and doubling each time. 5 retries was chosen to
allow for longer than expected waits for the interface to start
responding correctly; in testing, a single 5ms delay was sufficient to
fix the issue.

Closes: https://github.com/geoffreybennett/fcp-support/issues/2
Cc: stable@vger.kernel.org
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://patch.msgid.link/Z//7s9dKsmVxHzY2@m.b4.vu
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Geoffrey D. Bennett 2025-04-17 04:19:23 +09:30 • committed by Takashi Iwai
parent 494d0939b1
commit f406005e16
1 changed files with 7 additions and 0 deletions
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7
sound/usb/endpoint.c
View file

@ -926,6 +926,8 @@ static int endpoint_set_interface(struct snd_usb_audio *chip,
{
int altset = set ? ep->altsetting : 0;
int err;
int retries = 0;
const int max_retries = 5;
if (ep->iface_ref->altset == altset)
return 0;
@ -935,8 +937,13 @@ static int endpoint_set_interface(struct snd_usb_audio *chip,
usb_audio_dbg(chip, "Setting usb interface %d:%d for EP 0x%x\n",
ep->iface, altset, ep->ep_num);
retry:
err = usb_set_interface(chip->dev, ep->iface, altset);
if (err < 0) {
if (err == -EPROTO && ++retries <= max_retries) {
msleep(5 * (1 << (retries - 1)));
goto retry;
}
usb_audio_err_ratelimited(
chip, "%d:%d: usb_set_interface failed (%d)\n",
ep->iface, altset, err);