[PATCH] wifi: mt7601u: add vnd_reset parameter to fix probe failure on Tenda U2

[Herman Semenoff]

On certain MT7601U adapters, such as Tenda U2 and other newer hardware
revisions, driver initialization consistently fails during probe with
vendor request timeouts (-110 / -ETIMEDOUT):

  mt7601u 3-14:1.0: ASIC revision: 76010001 MAC revision: 76010500
  mt7601u 3-14:1.0: Firmware Version: 0.1.00 Build: 7640 Build time:
201302052146____
  mt7601u 3-14:1.0: Vendor request req:07 off:09a8 failed:-110
  mt7601u 3-14:1.0: Vendor request req:02 off:09a8 failed:-110
  mt7601u 3-14:1.0: Vendor request req:07 off:0734 failed:-110
  mt7601u 3-14:1.0: Vendor request req:42 off:0230 failed:-110
  mt7601u 3-14:1.0: probe with driver mt7601u failed with error -110

The failure occurs because mt7601u_load_firmware() unconditionally calls
mt7601u_vendor_reset() (MT_VEND_DEV_MODE_RESET) before uploading firmware
chunks. On these devices, issuing this vendor reset leaves the internal
MCU / FCE DMA engine in an unresponsive state after the first firmware
URB is submitted. As a result, reading MT_TX_CPU_FROM_FCE_CPU_DESC_IDX
(0x09a8) immediately times out.

Introduce a boolean module parameter 'vnd_reset' (default: false) to
make this vendor reset optional. When the vendor reset is skipped,
firmware upload succeeds and the wireless interface initializes normally.

Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1716301
Link: https://www.opena.tv/viewtopic.php?t=63919
Link: https://askubuntu.com/questions/1418850/the-problem-with-wi-fi-u2
Link: https://bbs.archlinux.org/viewtopic.php?id=224859
Link: https://reddit.com/r/archlinux/comments/1d6dfv5/mt7601u_usb_wifi_not_working/
Signed-off-by: Herman Semenoff <GermanAizek@xxxxxxxxxxxxx>
---
 drivers/net/wireless/mediatek/mt7601u/mcu.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt7601u/mcu.c
b/drivers/net/wireless/mediatek/mt7601u/mcu.c
index bad6ca821..abf4767f1 100644
--- a/drivers/net/wireless/mediatek/mt7601u/mcu.c
+++ b/drivers/net/wireless/mediatek/mt7601u/mcu.c
@@ -10,6 +10,7 @@
 #include <linux/delay.h>
 #include <linux/usb.h>
 #include <linux/skbuff.h>
+#include <linux/moduleparam.h>

 #include "mt7601u.h"
 #include "dma.h"
@@ -21,6 +22,14 @@
 #define MCU_FW_URB_SIZE (MCU_FW_URB_MAX_PAYLOAD + 12)
 #define MCU_RESP_URB_SIZE 1024

+static bool vnd_reset;
+module_param(vnd_reset, bool, 0644);
+MODULE_PARM_DESC(vnd_reset, "Perform vendor reset during firmware
upload (default: false)");
+
+static bool disable_usb_sg;
+module_param(disable_usb_sg, bool, 0644);
+MODULE_PARM_DESC(disable_usb_sg, "Unused compatibility parameter");
+
 static inline int firmware_running(struct mt7601u_dev *dev)
 {
  return mt7601u_rr(dev, MT_MCU_COM_REG0) == 1;
@@ -459,8 +468,10 @@ static int mt7601u_load_firmware(struct mt7601u_dev *dev)
  mt7601u_wr(dev, 0x94c, 0);
  mt7601u_wr(dev, MT_FCE_PSE_CTRL, 0);

- mt7601u_vendor_reset(dev);
- msleep(5);
+ if (vnd_reset) {
+ mt7601u_vendor_reset(dev);
+ msleep(5);
+ }

  mt7601u_wr(dev, 0xa44, 0);
  mt7601u_wr(dev, 0x230, 0x84210);
-- 
2.55.0