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ALSA: scarlett2: Add retry on -EPROTO from scarlett2_usb_tx()

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During communication with Focusrite Scarlett Gen 2/3/4 USB audio
interfaces, -EPROTO is sometimes returned from scarlett2_usb_tx(),
snd_usb_ctl_msg() which can cause initialisation and control
operations to fail intermittently.

This patch adds up to 5 retries in scarlett2_usb(), with a delay
starting at 5ms and doubling each time. This follows the same approach
as the fix for usb_set_interface() in endpoint.c (commit f406005e16
("ALSA: usb-audio: Add retry on -EPROTO from usb_set_interface()")),
which resolved similar -EPROTO issues during device initialisation,
and is the same approach as in fcp.c:fcp_usb().

Fixes: 9e4d5c1be2 ("ALSA: usb-audio: Scarlett Gen 2 mixer interface")
Closes: https://github.com/geoffreybennett/linux-fcp/issues/41
Cc: stable@vger.kernel.org
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://patch.msgid.link/aIdDO6ld50WQwNim@m.b4.vu
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Geoffrey D. Bennett 2025-07-28 19:00:35 +09:30 committed by Takashi Iwai
parent bd7814a4c0
commit 8a15ca0ca5
1 changed files with 7 additions and 0 deletions
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7
sound/usb/mixer_scarlett2.c
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@ -2351,6 +2351,8 @@ static int scarlett2_usb(
struct scarlett2_usb_packet *req, *resp = NULL;
size_t req_buf_size = struct_size(req, data, req_size);
size_t resp_buf_size = struct_size(resp, data, resp_size);
int retries = 0;
const int max_retries = 5;
int err;
req = kmalloc(req_buf_size, GFP_KERNEL);
@ -2374,10 +2376,15 @@ static int scarlett2_usb(
if (req_size)
memcpy(req->data, req_data, req_size);
retry:
err = scarlett2_usb_tx(dev, private->bInterfaceNumber,
req, req_buf_size);
if (err != req_buf_size) {
if (err == -EPROTO && ++retries <= max_retries) {
msleep(5 * (1 << (retries - 1)));
goto retry;
}
usb_audio_err(
mixer->chip,
"%s USB request result cmd %x was %d\n",