When a phone is hard-bricked, its primary bootloaders (like LK, fastboot, or xbl) are corrupted. The phone cannot boot into the Android OS or even a recovery menu. However, built directly into the silicon of the Qualcomm chip is a tiny, unerasable piece of code called the Primary Boot Loader (PBL).
When a Qualcomm-based Android smartphone or tablet becomes hard-bricked, it completely loses its ability to boot into the operating system, recovery mode, or the standard fastboot interface. To the user, the device looks like a completely unresponsive piece of "dead" metal and glass. However, deep within the Silicon Architecture of every Qualcomm Snapdragon processor lies a low-level safety valve designed to salvage such devices: . all qualcomm firehose file
This command loads the Firehose and resets the device—useful for "hard brick" recovery where no GPT table exists. When a phone is hard-bricked, its primary bootloaders