A second ifconfig wlan0 up brings the interface up without problems.
After a bit more debugging, the call trace is the following:
[10241.028130] zd1211rw 1-3:1.0: zd_chip_lock_phy_regs: error
ioread32(CR_REG1): -110
[10241.028140] zd1211rw 1-3:1.0: zd_switch_radio_on: failed to lock PHY regs
[10241.028148] zd1211rw 1-3:1.0: zd_op_start: failed to set radio on
Adding a 10 milliseconds delay between the call to set_mc_hash() and
zd_chip_switch_radio_on() allows successful interface bringups in all
cases and matches what the vendor driver did.
Acked-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi> Signed-off-by: Florian Fainelli <florian@openwrt.org> Signed-off-by: John W. Linville <linville@tuxdriver.com>