老外有这么几句:
Right now, best way to try El capitan with R9 380 is to install with integrated graphics (In BIOS, IGPU set as primary and CSM enabled). After finishing installation and initial setup of Mac OS, shutdown and change the display cable to graphics card.
Now the card will work (framebuffer injection is optional). Inject Intel should be used for now to get full QE/CI with R9 380. But monitor will get signal only after El Capitan fully loads. No signal even in BIOS. Hence make sure Timeout is set & Clover (UEFI Harddrive or UEFI USB) is set as first priority, before changing port. Note: This will not solve current problem of Tonga in El Capitan (not booting with PCIe as primary).