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

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[ Upstream commit 8a15ca0ca51399b652b1bbb23b590b220cf03d62 ]

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 f406005e162b
("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>
[ Applied retry logic around snd_usb_ctl_msg() instead of scarlett2_usb_tx() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Geoffrey D. Bennett 2025-08-13 10:44:47 -04:00 • committed by Greg Kroah-Hartman
commit 55e0bf41e9
1 changed files with 9 additions and 0 deletions
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9
sound/usb/mixer_scarlett_gen2.c
View file

@ -118,6 +118,8 @@
#define SCARLETT2_MIXER_MAX_VALUE \
((SCARLETT2_MIXER_MAX_DB - SCARLETT2_MIXER_MIN_DB) * 2)
#include <linux/delay.h>
/* map from (dB + 80) * 2 to mixer value
* for dB in 0 .. 172: int(8192 * pow(10, ((dB - 160) / 2 / 20)))
*/
@ -591,6 +593,8 @@ static int scarlett2_usb(
u16 req_buf_size = sizeof(struct scarlett2_usb_packet) + req_size;
u16 resp_buf_size = sizeof(struct scarlett2_usb_packet) + resp_size;
struct scarlett2_usb_packet *req = NULL, *resp = NULL;
int retries = 0;
const int max_retries = 5;
int err = 0;
req = kmalloc(req_buf_size, GFP_KERNEL);
@ -614,6 +618,7 @@ static int scarlett2_usb(
if (req_size)
memcpy(req->data, req_data, req_size);
retry:
err = snd_usb_ctl_msg(mixer->chip->dev,
usb_sndctrlpipe(mixer->chip->dev, 0),
SCARLETT2_USB_VENDOR_SPECIFIC_CMD_REQ,
@ -624,6 +629,10 @@ static int scarlett2_usb(
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,
"Scarlett Gen 2 USB request result cmd %x was %d\n",