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On some systems the BIOS will disable the VGA decode logic in the iGPU (via GMCH_CTRL) when an external GPU is used as the primary VGA device. In that case the iGPU will never claim any VGA register accesses, and any access we do will in fact end up on the external GPU. Don't go poking around in the other GPUs' registers. Note that (at least on the g4x board where I tested this) the BIOS forgets to set the VGACNTR VGA_DISP_DISABLE bit, and the reset value for said bit is 0. That apparently prevents the pipes from running, so we must still remember to set the bit, despite the VGA plane was never actually enabled. On more modern platforms (hsw+ maybe?) the reset value for VGACNTR was changed to have VGA_DISP_DISABLE already set. Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patch.msgid.link/20251208182637.334-6-ville.syrjala@linux.intel.com Acked-by: Jani Nikula <jani.nikula@intel.com>