[PATCH rtw-next v4] wifi: rtw88: usb: do not log transfers lost to a mode switch

[Mehmet Fide <mehmet.fide@gmail.com>]

From: Mehmet Fide <mehmet.fide@screeningeagle.com>

An RTL8822BU or RTL8822CU is asked to come back as a USB 3 device by
rtw_usb_switch_mode_new(). The chip powers off its MAC and leaves the bus
while the last control transfers of that sequence are still in flight, so
they complete with -EPROTO and the driver reports them as errors:

  rtw_8822bu 1-1:1.0: Firmware version 27.2.0, H2C version 13
  rtw_8822bu 1-1:1.0: write register 0xc4 failed with -71
  usb 1-1: USB disconnect, device number 2
  usbcore: registered new interface driver rtw_8822bu
  rtw_8822bu 1-1:1.0: Firmware version 27.2.0, H2C version 13

Register 0xc4 is REG_PAD_CTRL2 and the access losing the race is the
rtw_write32_set() that ends the switch sequence, a few milliseconds before
the disconnect. Which transfer gets caught varies from boot to boot: 0xc4
is in the "always on" section, so every write to it is followed by a second
one from rtw_usb_reg_sec(), and sometimes that is the one that fails:

  rtw_8822bu 1-1:1.0: rtw_usb_reg_sec: reg 0x4e0, usb write 1 fail,
  status: -71

Nothing is wrong here. The device re-enumerates, probes again and registers
normally, which is why rtw_usb_probe() already treats a non-zero return
from rtw_usb_switch_mode() as "Not a fail". On a USB 2 only port the
switch can never succeed, so the message returns on every boot and
everyone using such a port has to work out that it is harmless.

Mark the window in which the chip is expected to leave the bus and skip the
error reports for transfers that fall into it. The mark is a rtw_flags bit
set in rtw_usb_switch_mode(), so it covers both the new and the old switch
sequence, and it is cleared again right after them: the transfers that lose
the race are issued from inside the sequences, and anything that fails
later must be reported again.

Tested with an RTL8822BU (0x7392:0xb822) on a USB 2 root port of a TI AM62,
where the message appears exactly once per boot. With the patch both lines
are gone while the disconnect, the re-enumeration and the second firmware
load are unchanged.

Signed-off-by: Mehmet Fide <mehmet.fide@screeningeagle.com>
---
v4:
 - track the window with a RTW_FLAG_SWITCHING_USB_MODE bit in rtw_flags
   instead of a bool in struct rtw_usb, clear it unconditionally right
   after the switch sequences so later failures are reported again, and
   drop the comment block in usb.c (Ping-Ke Shih)
 - Signed-off-by switched to my work address to match my other patches
v3:
 - set the mark in rtw_usb_switch_mode() instead of in the two switch
   helpers (Ping-Ke Shih)

 drivers/net/wireless/realtek/rtw88/main.h |  2 ++
 drivers/net/wireless/realtek/rtw88/usb.c  | 22 +++++++++++++++++-----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/main.h b/drivers/net/wireless/realtek/rtw88/main.h
index c6e981ba7..fc3fb617c 100644
--- a/drivers/net/wireless/realtek/rtw88/main.h
+++ b/drivers/net/wireless/realtek/rtw88/main.h
@@ -377,6 +377,8 @@ enum rtw_flags {
 	RTW_FLAG_RESTARTING,
 	RTW_FLAG_RESTART_TRIGGERING,
 	RTW_FLAG_FORCE_LOWEST_RATE,
+	/* USB mode switch: the chip re-enumerates, transfers may be cut off */
+	RTW_FLAG_SWITCHING_USB_MODE,
 
 	NUM_OF_RTW_FLAGS,
 };
diff --git a/drivers/net/wireless/realtek/rtw88/usb.c b/drivers/net/wireless/realtek/rtw88/usb.c
index 64e1c3420..e13faecfb 100644
--- a/drivers/net/wireless/realtek/rtw88/usb.c
+++ b/drivers/net/wireless/realtek/rtw88/usb.c
@@ -64,7 +64,8 @@ static void rtw_usb_reg_sec(struct rtw_dev *rtwdev, u32 addr, __le32 *data)
 				 RTW_USB_CMD_REQ, RTW_USB_CMD_WRITE,
 				 t_reg, 0, data, t_len, 500);
 
-	if (status != t_len && status != -ENODEV)
+	if (status != t_len && status != -ENODEV &&
+	    !test_bit(RTW_FLAG_SWITCHING_USB_MODE, rtwdev->flags))
 		rtw_err(rtwdev, "%s: reg 0x%x, usb write %u fail, status: %d\n",
 			__func__, t_reg, t_len, status);
 }
@@ -90,7 +91,9 @@ static u32 rtw_usb_read(struct rtw_dev *rtwdev, u32 addr, u16 len)
 	ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
 			      RTW_USB_CMD_REQ, RTW_USB_CMD_READ, addr,
 			      RTW_USB_VENQT_CMD_IDX, data, len, 1000);
-	if (ret < 0 && ret != -ENODEV && count++ < 4)
+	if (ret < 0 && ret != -ENODEV &&
+	    !test_bit(RTW_FLAG_SWITCHING_USB_MODE, rtwdev->flags) &&
+	    count++ < 4)
 		rtw_err(rtwdev, "read register 0x%x failed with %d\n",
 			addr, ret);
 
@@ -140,7 +143,9 @@ static void rtw_usb_write(struct rtw_dev *rtwdev, u32 addr, u32 val, int len)
 	ret = usb_control_msg(udev, usb_sndctrlpipe(udev, 0),
 			      RTW_USB_CMD_REQ, RTW_USB_CMD_WRITE,
 			      addr, 0, data, len, 500);
-	if (ret < 0 && ret != -ENODEV && count++ < 4)
+	if (ret < 0 && ret != -ENODEV &&
+	    !test_bit(RTW_FLAG_SWITCHING_USB_MODE, rtwdev->flags) &&
+	    count++ < 4)
 		rtw_err(rtwdev, "write register 0x%x failed with %d\n",
 			addr, ret);
 
@@ -1173,6 +1178,7 @@ static bool rtw_usb3_chip_new(u8 chip_id)
 static int rtw_usb_switch_mode(struct rtw_dev *rtwdev)
 {
 	u8 id = rtwdev->chip->id;
+	int ret;
 
 	if (!rtw_usb3_chip_new(id) && !rtw_usb3_chip_old(id))
 		return 0;
@@ -1189,10 +1195,16 @@ static int rtw_usb_switch_mode(struct rtw_dev *rtwdev)
 		return 0;
 	}
 
+	set_bit(RTW_FLAG_SWITCHING_USB_MODE, rtwdev->flags);
+
 	if (rtw_usb3_chip_old(id))
-		return rtw_usb_switch_mode_old(rtwdev);
+		ret = rtw_usb_switch_mode_old(rtwdev);
 	else
-		return rtw_usb_switch_mode_new(rtwdev);
+		ret = rtw_usb_switch_mode_new(rtwdev);
+
+	clear_bit(RTW_FLAG_SWITCHING_USB_MODE, rtwdev->flags);
+
+	return ret;
 }
 
 #define USB_REG_PAGE	0xf4
-- 
2.54.0