GrUB2 can be told to leave the screen in the graphics mode it has been using (or any other one), via "set gfxpayload=keep" (or suitable variants thereof). In this case we can avoid doing another mode switch ourselves. This in particular avoids possibly setting the screen to a less desirable mode: On one of my test systems the set of modes reported available by the VESA BIOS depends on whether the interposed KVM switch has that machine set as the active one. If it's not active, only modes up to 1024x768 get reported, while when active 1280x1024 modes are also included. For things to always work with an explicitly specified mode (via the "vga=" option), that mode therefore needs be a 1024x768 one. For some reason this only works for me with "multiboot2" (and "module2"); "multiboot" (and "module") still forces the screen into text mode, despite my reading of the sources suggesting otherwise. For starters I'm limiting this to graphics modes; I do think this ought to also work for text modes, but - I can't tell whether GrUB2 can set any text mode other than 80x25 (I've only found plain "text" to be valid as a "gfxpayload" setting), - I'm uncertain whether supporting that is worth it, since I'm uncertain how many people would be running their systems/screens in text mode, - we're pretty close to needing a 4th trampoline page, so I'd like to limit the amount of added code. For starters I'm also limiting mode information retrieval to raw BIOS accesses. This will allow things to work (in principle) also with other boot environments where a graphics mode can be left in place. The downside is that this then still is dependent upon switching back to real mode, so retrieving the needed information from multiboot info is likely going to be desirable down the road. Signed-off-by: Jan Beulich <firstname.lastname@example.org> --- I'm not convinced boot_vid_mode really needs setting here; I'm doing so mainly because setvesabysize also does. --- a/xen/arch/x86/boot/video.S +++ b/xen/arch/x86/boot/video.S @@ -575,7 +575,6 @@ set14: movw $0x1111, %ax movb $0x01, %ah # Define cursor scan lines 11-12 movw $0x0b0c, %cx int $0x10 -set_current: stc ret @@ -693,6 +692,39 @@ vga_modes: .word VIDEO_80x60, 0x50,0x3c,0 # 80x60 vga_modes_end: +# If the current mode is a VESA graphics one, obtain its parameters. +set_current: + leaw vesa_glob_info, %di + movw $0x4f00, %ax + int $0x10 + cmpw $0x004f, %ax + jne .Lsetc_done + + movw $0x4f03, %ax + int $0x10 + cmpw $0x004f, %ax + jne .Lsetc_done + + leaw vesa_mode_info, %di # Get mode information structure + movw %bx, %cx + movw $0x4f01, %ax + int $0x10 + cmpw $0x004f, %ax + jne .Lsetc_done + + movb (%di), %al # Check mode attributes + andb $0x99, %al + cmpb $0x99, %al + jne .Lsetc_done # Doh! No linear frame buffer + + movb $1, bootsym(graphic_mode) + movw %bx, bootsym(boot_vid_mode) + movw %bx, bootsym(video_mode) + +.Lsetc_done: + stc + ret + # Detect VESA modes. vesa_modes: movw %di, %bp # BP=original mode table end
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