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[bug #50911] i386-pc: ability to probe extra VBE modes

From: felix
Subject: [bug #50911] i386-pc: ability to probe extra VBE modes
Date: Tue, 2 May 2017 04:27:05 -0400 (EDT)
User-agent: Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.135 Safari/537.36 Edge/12.10136


                 Summary: i386-pc: ability to probe extra VBE modes
                 Project: GNU GRUB
            Submitted by: felix_s
            Submitted on: Tue 02 May 2017 08:27:04 AM UTC
                Category: User Interface
                Severity: Major
                Priority: 5 - Normal
              Item Group: Feature Request
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: Git master
         Reproducibility: Every Time
         Planned Release: None



Some VBE implementations may fail to advertise the availability of all
supported video modes via the interrupt call 0x10/ax=0x4f00. I used to have a
laptop with Intel integrated graphics which did just that: mode
0x17d/0x17e/0x17f set the highest possible resolution on the available display
(8bpp, 16bpp, 32bpp respectively), but I only found it out by brute-forcing
queries to the interrupt 0x10/ax=0x4f01 call.

I can work this around by patching the video BIOS (that is, unlocking writes
to the [0xc0000, 0xcffff] RAM range, patching the modes list and locking the
range again), but this is quite ugly, hardware-specific and potentially
dangerous. I'd rather would have set a variable in GRUB which would make the
vbe module probe modes of my choosing in addition to (or maybe even instead
of?) the ones returned from the interrupt 0x10/ax=0x4f00 call.


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