Allwinner A64 has a slightly modified version of the Allwinner MMC controller.
It do not have "output" or "sample" clock input, instead, it can calibrate the
delay internally.
This series of patch added the calibrate feature to the sunxi-mmc driver. It
is based on works by Andre Przywara <andre.przywara@xxxxxxx>, and now it
depends on the patch set sent recently by Hans de Goede <hdegoede@xxxxxxxxxx>,
which disabled "output" and "sample" clock on A10/13.
( http://lists.infradead.org/pipermail/linux-arm-kernel/2016-July/446187.html )
As the clock and device tree patch for Allwinner A64 is not yet merged, the
patch set contains no patch to enable it.