Re: [gentoo-user] Re: about boot with framebuffer

[Alan McKinnon <alan.mckinnon@gmail.com>]

On Monday 04 July 2011 14:15:12 Mark Knecht did opine thusly:
> On Mon, Jul 4, 2011 at 1:57 PM, Alan McKinnon 
<alan.mckinnon@gmail.com> wrote:
> > On Monday 04 July 2011 13:47:28 Mark Knecht did opine thusly:
> >> On Mon, Jul 4, 2011 at 1:40 PM, Alan McKinnon



> >> so does bootsplash run using framebuffer or is it completely
> >> different?
> > 
> > I have no idea actually. I could say it must run in a
> > framebuffer-like abstraction but that is obvious and doesn't
> > tell you anything you don't already know.
> > 
> > Spock is the dev that knows most about these things, a good
> > first
> > research point would be to search his name and find related
> > docs.
> > 
> > Sorry I can't be more help - I have the concepts in my head but
> > not the facts
> 
> I appreciate the info. No worries about that.
> 
> I think the other point I'm missing here is whether KMS is actually
> implementing anything graphical, like a framebuffer, or whether it's
> just moving _choices_ about graphics into the kernel and out of X?

By definition a framebuffer is a chunk of memory, and my understanding 
is that KMS does implement one (nouveau definitely provides a 
framebuffer, and it conflicts with all other framebuffers - you can't 
have more than one in the kernel at all). The clue is in the name: 
Kernel Mode Switching. It deals with all the low-level commands to set 
modes in the graphics card so that X doesn't have to do it itself.

> 
> I have an Intel i5-661/Intel MB based machine which is the only one
> I use KMS for at this time. On that machine I was instructed to use
> KMS by the Intel-Gfx devs to get their driver working at all. A
> nice side benefit was that it resulted in better text in the
> console during boot. However I don't see anything 'graphics like'
> on that box just using KMS so I suspect that while I've enabled
> technology that allows the kernel to manage graphics that I haven't
> told the kernel to actually do so. I don't know though.

When you speak of graphics in the context of framebuffers and 
consoles, it's better to think in terms of "able to do what graphics 
does" i.e. address a gigantic number of pixels individually. The fact 
that you are not running any software capable of rendering graphics 
doesn't reduce the fact that the means to do is there.

> All of my other machines are NVidia based and use the closed source
> driver so my understanding on those is that KMS doesn't apply.

Yes, that's true.

nVidia does it's own bizarre weird stuff that will forever more be 
incompatible with the entire free software world <sigh>


> I'm curious, however, about my Gentoo VMs. Can KMS run on a VM's
> kernel and do anything useful there? This is more for learning and
> not about any practical need at this time.

From my understanding, this topic gets yucky. There's a whole bunch of 
ways this could be done, from software emulation to para-
virtualization to full virtualization. Emulation is easy - KMS in the 
guest sees what looks for all the world like hardware so everything 
works if KMS supports the emulated card (albeit slowly). For 
everything else, you'd need kernel drivers intercepting efforts to 
talk to the hardware and be traffic cop. My brain is already spinning 
on this so please excuse me while I go dunk my head in a bucket and 
not think about it anymore :-)







> 
> Cheers,
> Mark
-- 
alan dot mckinnon at gmail dot com