Linux Patch Proposed To Double Raspberry Pi 4 Transfer Speed To eMMC/SD Storage
Tobias sent out on the kernel mailing list that both micro SD and eMMC with the Raspberry Pi 4 is running in single data rate mode only. However, the controller and the board circuitry appear to support the double data rate (DDR) mode just fine. He added that he even checked on the signal integrity on the data lines for the micro SD card slot and didn't find any issues.
Thus the Manjaro developer sent out a patch enabling the DDR modes on the Raspberry Pi 4 to its respective Device Tree file. This should theoretically double the transfer speeds to the eMMC/SD storage. So far no kernel developers or Raspberry Pi Foundation staff have commented on the proposed patches for the mainline Linux kernel.