- External reference: https://www.thecustomdroid.com/qualcomm-edl-mode-guide/
What is EDL Mode and How to Boot your Qualcomm Android Device into it
Android phones and tablets equipped with Qualcomm chipset contain a special boot mode which could be used force-flash firmware files for the purpose of unbricking or restoring the stock ROM
EDL or Emergency DownLoad Mode is a special boot mode in Qualcomm Android devices that allows OEMs to force-flash firmware files
EDL implements Qualcomm’s Sahara or Firehose protocol (on modern devices) to accept OEM-digitally-signed programmer in ELF file format (or in MBN file format on older devices).
When in this mode, the device identifies itself as “Qualcomm HS-USB QDLoader 9008” over a USB connection.
EDL itself is a part of the Primary Bootloader (PBL) on Qualcomm Devices. Unlike Fastboot, Download, and Recovery modes on Android, which reside in the Secondary Bootloader (SBL), PBL resides within the ROM and so it could not be corrupted due to software errors (again, like a wrong flash).
adb reboot edl
when your phone cannot enter the OS but can boot into Fastboot mode
fastboot oem edl
Once your Qualcomm Android device has entered EDL mode, you can connect it to the PC and use tools like QPST or QFIL to flash firmware files to unbrick or restore stock ROM