[haiku-development] Re: S3 Video Driver
- From: "Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Wed, 05 Mar 2008 10:42:10 +0100 CET
Gerald Zajac <zajacg@xxxxxxxxxxxxx> wrote:
> > The PIO mode is a performance problem in itself - using a syscall
> > per
> > port access isn't that problematic; and you could always turn off
> > acceleration if it really would be a problem. Being able to change
> > the
> > resolution would be a good start, though, I think.
> > But it's your decision, anyway! :-)
> Hi Axel! How do you envision accessing the PIO ports in the kernel
> module? Would it be done by creating a pci_module_info object during
> startup, and then using the pci_module_info read_io and write_io
> functions to access the PIO ports? I'm currently using this method
> during startup to enable MMIO on the Trio and Virge chips. Or is
> there
> another simpler way of accessing these ports?
You would need to use the ISA bus module, and then add ioctl's to your
driver that lets the accelerant use the {write|read}_io_{8|16|32}
functions much like SAVAGE_{GET|SET}_PCI.
In the accelerant, you could then have a handy function that hides the
ioctl() from you again.
> If acceleration for this chip is turned off and this way of accessing
> the PIO ports is used only for changing the resolution, I'm wondering
> why the VESA driver could not be enhanced to change the resolution?
> That way the VESA driver could handle all these older video chips
> where
> it is questionable whether it is worth the effort to write code to
> handle them in other video drivers.
Every graphics card is programmed differently when you're using PIO.
There is a VESA VBE interface that you can use on most cards to change
the resolution, but that requires you to use x86 real mode (or virtual
x86 mode) - and it's quite an effort to add virtual mode support just
for this IMO.
There is a newer VBE3 interface that also offers a protected mode
environment, but AFAIU only very few graphics cards implement this
correctly or completely. Even though it might be enough for mode
setting, I haven't looked at it that closely (VBE3 also allows for
hardware acceleration). In any case, this wouldn't work with older
cards, anyway.
Bye,
Axel.
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