emmc 4.4x fast boot question

hi experts,

trying to use imx6q "eMMC Fast Boot" mode without success. Can't get any clarification from freescale still, so i try here.

From the imx6q boot flow diagram seems there can be some gain using it.

Once studying on the Micron eMMC i have connected to imx6q, (as per
TN-52-06: Booting from Embedded MMC - JEDEC 4.41 online pdf) i see
this mode is just called "boot mode" or "alternate boot mode", and seems to allow to boot from SLC mmcblk0boot0 or mmcblk0boot1 partitions setting EXT_CSD[179] partition to 1 or 2 in bits 3to5.

In this way i can boot from mmcblk0boot0. but if i enable the hw imx6q GPIO BOOT_CFG1[4] "Fast Boot" mode, i cannot boot anymore.

If i look signal with scope, booting i don't see the initial CMD pulled low as should be for the Boot mode.
If i enable imx6q "fast boot" (BOOT_CFG1[4]) i just see a continuos and long train of bits on both CMD and CLK from the reset.

So i can boot from special SLC mmcblk0boot0 but without imx6
"Fast Boot" enabled. So i am trying to understand why this Fast Boot feature (BOOT_CFG1[4] set) can't be used.

In case you can give any help on this it will be really appreciated.

Best regards,
Angelo Dureghello