LCA: Updates on the X Window System [LWN.net]

LCA: Updates on the X Window System

Posted Jan 23, 2007 0:16 UTC (Tue) by neilbrown (subscriber, #359)
In reply to: LCA: Updates on the X Window System by jwb
Parent article: LCA: Updates on the X Window System

The current Intel driver uses the Video BIOS to get mode settings. If your Video bios has bad information, then X will have trouble setting the mode properly.

My new notebook has a 1920x1200 screen, but the vbios doesn't know about that size, only 1600x1200 or 1920x1400. So it isn't exactly Intel's fault
if the hardware manufacturer provides a broken bios.

Fortunately there is a program "915resolution" which "corrects" the VBIOS. I ran it and suddenly 1920x1200 worked just fine.

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LCA: Updates on the X Window System

Posted Jan 23, 2007 0:20 UTC (Tue) by jwb (guest, #15467) [Link] (7 responses)

Of course it's Intel's fault. My motherboard is made by Intel, my graphics are made by Intel, I download my BIOS from Intel's site, and Intel's name and logo are all over the place. They can hardly claim that the BIOS implementation is out of their hands.

Also, 915resolution doesn't work on the G965.

LCA: Updates on the X Window System

Posted Jan 23, 2007 1:32 UTC (Tue) by drag (guest, #31333) [Link] (6 responses)

Ya.. it's definately Intel's problem.

Their hardware, their design, their vbios. Other manufacturers just use what they get from Intel.

LCA: Updates on the X Window System

Posted Jan 23, 2007 1:48 UTC (Tue) by neilbrown (subscriber, #359) [Link] (5 responses)

My understanding from Keith's talk at LCA is that the Intel graphics chip
doesn't actually control mode setting at all. It somehow leaves that for
some other glue chip that the motherboard manufacturer needs to provide.
(Apparently this is similar to the AC97 sound architecture where the
analogue bits were not in the Intel chipset, only the digital bits).

The interface to these mode-setting glue chips is not standardised
so everybody does it differently. So for Xorg to be able to do
mode setting, it with has to know about how all the different glue
chips work (Which is what the new mode-setting branch of the driver tries)
or it needs help from the VBIOS (which is what the 'stable' branch does).

So maybe it is Intel's fault for not standardising the interface properly,
and very likely it is Intel's fault if you have an Intel motherboard, but
the situation doesn't seem to be as straight forward as one might like it to be.

LCA: Updates on the X Window System

Posted Jan 23, 2007 6:51 UTC (Tue) by keithp (subscriber, #5140) [Link] (4 responses)

Intel chips have some outputs built-in and rely on external chips for other outputs. G965 has only VGA built-in, and relies on SDVO for DVI and TV-out. Mobile chips (915GM, 945GM) have built-in LVDS and TV out as well, so there's no external chip driver needed for most operations.

The Intel driver has relied for far too long on BIOS-based modesetting, and after I joined Intel, replacing that became our highest priority. While initial support for LVDS and VGA was running early last year, getting the remaining outputs working correctly has taken a long time. Of course, all of that would have been a lot easier if we hadn't also been working on RandR 1.2 at the same time.

LCA: Updates on the X Window System

Posted Jan 23, 2007 14:43 UTC (Tue) by sylware (guest, #35259) [Link] (2 responses)

BTW, why "CRTC"? In randr 1.2, "CRTC"s are not really dealing only with Cathod Ray Tubes. Maybe a more appropriate name should be chosen since you have control over the API. I do realize it's a rather super minor detail.

LCA: Updates on the X Window System

Posted Jan 23, 2007 15:51 UTC (Tue) by jzbiciak (guest, #5246) [Link]

And what about these plotters that are actually printers, SCSI disks that are actually flash drives, and TTYs that haven't seen a teletype in decades? Next you'll be telling me that the primary use of TAR files really is tape backup! ;-) ;-) ;-)

LCA: Updates on the X Window System

Posted Jan 23, 2007 18:02 UTC (Tue) by bronson (subscriber, #4806) [Link]

Because "CRTC" is an industry term that is older than I am. All video driver writers know what you're talking about when you say "CRTC" regardless of platform or API.

Besides, what should it be replaced with? LCDC? And then replace that 5 years later with LEDC? :)

LCA: Updates on the X Window System

Posted Jan 23, 2007 23:51 UTC (Tue) by gdt (subscriber, #6284) [Link]

Thank you Keith, as the Intel driver's BIOS calls are somewhat problematic on the Mac Mini (requiring the installation of the Bootcamp BIOS emulator, thus during-boot keystrokes are required to select the Linux operating system else it boots MacOS).

LCA: Updates on the X Window System

Posted Jan 25, 2007 19:23 UTC (Thu) by kamil (guest, #3802) [Link]

Well, my notebook with 855GM chipset has an 1024x768 LCD, and that mode is in the BIOS. But I now have a 20" widescreen Dell flatpanel, with a native resolution of 1680x1050, which, not surprisingly, is not in the Video BIOS.

You are right that it's not the "fault" of Video BIOS. It is simply a poor design of the Intel's X video driver. Yes, I know they are fixing it; the problem is that it's been in the "being fixed" stage for >6 months already. Obviously, it's still better then nothing; I'm periodically downloading the current modesetting branch, but have yet to encounter a version that would work flawlessly. The latest one I'm running now (from two weeks ago) disables XVideo at my resolution due to some "double-wide pipe mode" nonsense (luckily commenting it out in the source fixes it), and it sometimes locks the machine up for good if I don't use it for a while.

Oh, and 855resolution doesn't work for me. I think the problem is that it adjusts the resolution, but not the frequency. Dell 2007WFP only accepts 1680x1050 at precisely 60Hz, which is apparently not what the laptop is sending it if I use 855resolution.