LCA: Graphics driver ponies

Posted Jan 28, 2010 4:36 UTC (Thu) by thedevil (guest, #32913)
Parent article: LCA: Graphics driver ponies

I have 2 comments about the ATI side. 1. I think what in the staging tree in 2.6.32 is just the option of making KMS the default. Even if you don't enable the staging tree at all you can already use KMS just by doing

echo 'options radeon modeset=1' >> /etc/modprobe.d/local-radeon.conf

2. I tried it, it works fine in X, and I see no problems as long as my virtual consoles start in old-fashioned text mode. They actually seem to be changed to an internal framebuffer mode as soon as I switch to them with Alt+Ctl+Fn . But I get a very unexpected result when I enable *both* KMS and vesafb. When I switch to a virtual console with Alt+Ctl+Fn, my monitor displays the "No signal" message and goes to sleep! So, based on this experience I am not going to use KMS quite yet.

LCA: Graphics driver ponies

Posted Jan 28, 2010 5:01 UTC (Thu) by BenHutchings (subscriber, #37955) [Link] (7 responses)

The DRI+KMS graphics drivers will conflict with framebuffer drivers for the same hardware. The kernel only allows one driver to bind to each PCI device and normally that prevents you from making this mistake. vesafb is an exception because it doesn't bind to a specific PCI device, but you should not expect it to work.

LCA: Graphics driver ponies

Posted Jan 28, 2010 6:43 UTC (Thu) by thedevil (guest, #32913) [Link] (6 responses)

Hmm. Maybe my memory is really going to $@#! due to middle age, but I seem to remember that saner switching between X and VCs was one of the selling points of KMS. But if that means you have to stay in 80x25 for the VCs it's not very persuasive.

LCA: Graphics driver ponies

Posted Jan 28, 2010 13:29 UTC (Thu) by xav (guest, #18536) [Link] (4 responses)

By default on my system KMS sets the console framebuffer to 1900x1200, which makes fro a quite high res text console (I don't know how much, but far more than 80x25).

LCA: Graphics driver ponies

Posted Jan 28, 2010 14:57 UTC (Thu) by nix (subscriber, #2304) [Link] (2 responses)

I do wonder how to set the resolution to something nonstandard. As far as
I can tell with Radeon KMS there is no way: the resolution the monitor
prefers is always selected. This is normally fine for those of us with
LCDs, but for the poor sods stuck on CRTs it seems suboptimal.

(but, yes, a nice fb console with huge numbers of rows and columns which
does not bugger up X acceleration is a major plus of KMS. Another major
plus.)

LCA: Graphics driver ponies

Posted Jan 28, 2010 21:52 UTC (Thu) by michich (guest, #17902) [Link] (1 responses)

Boot parameter video=800x600 works for me with Radeon KMS. See Documentation/fb/modedb.txt.

LCA: Graphics driver ponies

Posted Jan 28, 2010 22:53 UTC (Thu) by nix (subscriber, #2304) [Link]

OK, no wonder I couldn't find the docs. fb/modedb.txt is, uh, not the most
obvious of places :)

(though 800x600 is the last-ditch fallback resolution in any case, so
perhaps not the best one to test with.)

LCA: Graphics driver ponies

Posted Feb 2, 2010 1:38 UTC (Tue) by Spudd86 (subscriber, #51683) [Link]

If the text is too small change the console font to something bigger.

LCA: Graphics driver ponies

Posted Jan 28, 2010 20:59 UTC (Thu) by BenHutchings (subscriber, #37955) [Link]

You set it through the KMS driver, not vesafb. (But don't ask me how!)

LCA: Graphics driver ponies

Posted Jan 28, 2010 7:42 UTC (Thu) by airlied (subscriber, #9104) [Link] (3 responses)

If you don't enable KMS by default using the staging option, udev won't load it, so you'll need to load it by hand before starting X. This is really why distros need to ship support for KMS by default or don't bother.

So just load it by default somewhere before X starts and get a hires console.

LCA: Graphics driver ponies

Posted Jan 29, 2010 5:05 UTC (Fri) by thedevil (guest, #32913) [Link] (2 responses)

But it doesn't work! It gives me the same "No signal" behavior as when I enable vesafb.

I guess I should report this, but where?

LCA: Graphics driver ponies

Posted Jan 30, 2010 4:09 UTC (Sat) by thedevil (guest, #32913) [Link] (1 responses)

Solved! It turns out I haven't selected fbcon in the kernel config. So this is really a bug in the kernel build system: drm + kms should autoselect fbcon.

LCA: Graphics driver ponies

Posted Jan 30, 2010 11:36 UTC (Sat) by chris.wilson (guest, #42619) [Link]

It does, but only if you have not also selected to optimize for small/embedded systems where you can opt out of the overhead of allocating a framebuffer for the console.

config DRM_KMS_HELPER
tristate
depends on DRM
select FB
select FRAMEBUFFER_CONSOLE if !EMBEDDED

LCA: Graphics driver ponies

Posted Feb 2, 2010 1:37 UTC (Tue) by Spudd86 (subscriber, #51683) [Link]

err, you REALLY ought to make sure the KMS driver is controlling your consoles... if somehow you managed to end up binding vesafb to your consoles with the radeon DRI stuff assuming KMS bad things would happen...

You CAN'T use both at the same time, KMS implies framebuffer console with the KMS based driver controlling it. (And vesafb should do nothing)