After I insert SDcard, I boot,
I can see

mmc0: host does not support reading read-only switch. Assuming write-
enable.
mmcblk0: mmc0:e624 SU01G 992000KiB
mmcblk0:<7>mmc0: starting CMD18 arg 00000000 flags 00000035

and
I tried to mount
mount -t vfat /dev/mmcblk0p1 /mnt
mount: mounting /dev/mmcblk0p1 on /mnt failed

or
mount -t vfat /dev/mmcblk0 /mnt
mount: mounting /dev/mmcblk0 on /mnt failed

how can I mount the SDcard ?

Thanks in advance!!

Can you do low-level i/o through /dev/mmcblk0 (for example, dd)?
Is the /dev/mmcblk0p1 device shown in /proc/partitions?
Add debug to mmc driver and see what happens.