Commit f406005e authored by Geoffrey D. Bennett's avatar Geoffrey D. Bennett Committed by Takashi Iwai
Browse files

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

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: default avatarGeoffrey D. Bennett <g@b4.vu>
Link: https://patch.msgid.link/Z//7s9dKsmVxHzY2@m.b4.vu


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 494d0939

sound/usb/endpoint.c

+7 −0
Original line number Diff line number Diff line
@@ -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);