If there is some detect on ethernet will cause kernel freeze

Hi there is some problems on ethernet controller. My board use lan8720a and it do not support dynamic control ethernent clock well. So i let it normal on. And it solve the problem on kernel support by freescale.But it failed on uc 16. The ethernet port seem well but kernel freeze at here:

[ 3.412416] PPP Deflate Compression module registered [ 3.417746] PPP MPPE Compression module registered [ 3.422851] NET: Registered protocol family 24 [ 3.427632] ehci_hcd: USB 2.0 ‘Enhanced’ Host Controller (EHCI) Driver [ 3.434389] ehci-pci: EHCI PCI platform driver [ 3.439222] ehci-mxc: Freescale On-Chip EHCI Host driver [ 3.446244] usbcore: registered new interface driver usb-storage [ 3.453052] usbcore: registered new interface driver usbserial_generic [ 3.460276] usbserial: USB Serial support registered for generic [ 3.466906] usbcore: registered new interface driver option [ 3.472931] usbserial: USB Serial support registered for GSM modem (1-port) [ 3.480172] usbcore: registered new interface driver quatech2 [ 3.486346] usbserial: USB Serial support registered for Quatech 2nd gen USB to Serial Driver

if i use only one ethernet port it’s run well. the kernel is here. the drivers seem no different from freescale’s kernel. and i change the driver at /drivers/net/ethernet/freescale/fec_main.c image

Do someone have some idea about this problem?Thanks.