I work on a custom iMX6 board derived from sabre_SD design and I use u-boot and yocto Dora with the 3.0.35_4.1.0 kernel. I have two hardware versions of this board. The first version is provided with a 8GB eMMC 5.0 and works fine, my problem is with the second version. It is provided with a 4GB eMMC 4.51 (and this is the only difference), I can use u-boot and save environment on the eMMC but I can't boot linux. I use an external microSD card to host u-boot ,the uImage file and the rootfs, uboot and uImage are loaded correctly but on the 4GB version the boot fails after udev starts. The error is always different : udev or mount.sh segmentation fault, core dump, time out on mmc, pagination error ... on my lvds screen the psplash loading bar freezes at different positions, sometimes psplash doesn't load and it freezes on the for penguins console screen. But, if you are patient enough, if you reboot the board again and again, you can boot the board (about one time on twenty) on the fsl-image-gui sato desktop and you can mount and use the eMMC.
Do you have an idea of where could be the problem ?
I tried on different boards, I tried to check with different 4GB eMMC (Sandisk, kingston v4.5 and 4.51), I tried to slow down the bus ... Nothing works at this time and I found nothing about this on google and freescale community search.