Simon Thum <[email protected]> writes: > AFAIK the DDC stuff was endorsed in 2.0, so it's probably just a > heuristic, not a hard limit. I'm not the maintainer but I guess a good > patch is appreciated. IIRC the vbe bios does advertise if it has the > DDC extension, which should be a preferable 'heuristic'.
As I understand from specification [1], the DDC supplements VESA Video BIOS and isn't included into the VESA 1.2 [2] or VESA 2.0 [3]. The presence of DDC can be verified by calling function 4F15h of int10h and examining the contents of AX register. If AL != 4FH or AH != 0 after calling then DDC isn't supported. This procedure is described in Section 6, 6.1 of [2] and 4, 4.1 of [3] and, therefore, actual for both VESA 2.0 and VESA 1.2. Function vbeProbeDDC (hw/xfree86/vbe/vbe.c) just doing this stuff and is called from vbeReadEDID which is called from vbeDoEDID just after VBE version check in question. VESA 1.2 specification defines subfunctions from 00h to 07h, and subfunctions 08h-FFh are declared as reserved [2]. VESA 2.0 defines subfunctions 00h-0Fh, and 10-FFh are reserved for VBE Supplemental Specifications [3]. DDC's subfunction number is 15h. So I conclude that the VBE version in vbeDoEDID can be lowered to 1.2 as soon as the procedure for verifying the presence of subfunction (15h in the case of DDC) is defined in VESA 1.2 and VESA 2.0 specs. [1] DDC - http://www.vesa.org/public/VBE/VBEDDC11.PDF [2] VESA 1.2 - http://docs.ruudkoot.nl/vesasp12.txt [3] VESA 2.0 - http://docs.ruudkoot.nl/vbe20.txt _______________________________________________ xorg mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/xorg
