EDL method is a way of extracting physical images from phones with Qualcomm chipsets. This option does not require the phone to be rooted and works on most of the Qualcomm-equipped devices.
Every device has a specific way to enter EDL mode:
short test points
using the command “adb reboot edl”
When in this mode, the device identifies itself as “Qualcomm HS-USB QDLoader 9008” in device manager.
On the main screen, select “Security bypassing”.
Choose a security bypassing approach.
Select the exact device model from the list and choose “Get physical dump from EDL”. Follow on-screen instructions. If the device is not listed, try another approach.
If the chipset is known, select it from the list. Then follow on-screen instructions.
Follow on-screen instructions. For this approach, you will need to get by your self EDL programmer for the given device.
With the release of the MIUI 8.0 was the EDL access using the ADB command "adb reboot edl' suspended.
In some cases might also work ADB command "fastboot oem edl" for this you will need an unlocked bootloader.
Test points for the Xiaomi devices: http://en.miui.com/thread-638042-1-1.html
Additional articles about EDL and advanced methods: