[PATCH 5.4.y] ALSA: scarlett2: Add retry on -EPROTO from scarlett2_usb_tx()

[Sasha Levin <sashal@kernel.org>]

From: "Geoffrey D. Bennett" <g@b4.vu>

[ 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: 9e4d5c1be21f ("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>
---
 sound/usb/mixer_scarlett_gen2.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index 6d8ef3aa99b5..3b225430bfad 100644
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -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",
-- 
2.39.5