Hi Frank I solved the problem by changing the major number of wifi device as 155.
For this operation, I change #define WIFI_DEV_MAJOR 155 defination in the files
linux-mt/drivers/misc/mediatek/connectivity/common/combo/linux/wmt_chrdev_wifi.c
linux-mt/drivers/misc/mediatek/connectivity/common/conn_soc/linux/pub/wmt_chrdev_wifi.c
and I have rebuiled the kernel. The crash of spidev and wifi_dev has been removed.
cat /proc/devices
153 spi
154 mtk_wcn_detect
155 mtk_wmt_WIFI_chrdev
dmesg |grep -i wifi
[ 21.342303] [MTK-WIFI] WIFI_init: mtk_wmt_WIFI_chrdev driver(major 155) installed.
[ 21.342312] [WLAN-MOD-INIT][I]do_wlan_drv_init:WMT-WIFI char dev init, ret:0
[ 23.376886] [MTK-WIFI] WIFI_open: WIFI_open: major 155 minor 0 (pid 848)
[ 23.376931] [MTK-WIFI] WIFI_write: WIFI_write 1
[ 25.638586] [WMT-FUNC][W]wmt_func_wifi_on:WMT-FUNC: wmt wlan func on before wlan probe
[ 26.772321] [MTK-WIFI] register_set_p2p_mode_handler: (pid 858) register set p2p mode handler c07223e4
[ 26.772349] [WMT-FUNC][W]wmt_func_wifi_on:WMT-FUNC: wmt call wlan probe ok
[ 26.772448] [MTK-WIFI] WIFI_write: WMT turn on WIFI success!
[ 26.772470] [MTK-WIFI] WIFI_close: WIFI_close: major 155 minor 0 (pid 848)