On Thu, 5 Feb 2004, [iso-8859-1] Suresh Chandra Mannava wrote:
> Does XFree86 need kernel framebuffer support? Or it's
> have its own framebuffer interface?
>
> what will be the performance gain if we use kernel
> framebuffer support?
>
> If we use a particular server for example Mach64
> server, it has its own (user mode) graphic driver
> which supports graphic card. Does it still requires
> any type of support from the kernel?
XFree86 does not in general need kernel framebuffer support for
hardware which is supported by an XFree86 driver, as it has its own
framebuffer interface.
There are two cases where XFree86 does need kernel support.
* Chipsets like the i810/i815/i835/... family have no framebuffer memory
but use main system memory for the framebuffer. This requires agpgart
support from the kernel.
* Most hardware 3D acceleration, whether DRI-based or manufacturer
supplied, uses kernel support for access to the chip.
I think this is more to control access to the graphics
engine than to the frame buffer directly.
The XFree86 mach64 driver does not use kernel support, but there are
alternative drivers such as GATOS, which provide features which ours does
not have - TV out and hardware 3D. I'm hazy on the details, but some of
these use kernel modules, including agpgart, or for pcicards a "pcigart"
module.
There is an XFree86 driver (fbdev IIRC) which uses kernel framebuffer
support, and some XFree86 drivers can work with a kernel framebuffer
when reqiested.
The kernel has extra support for some hardware, but in general it
doesn't use the graphics engine much, so is fairly slow.
I don't have direct experience, but I'd expect that the XFree86 drivers
are faster than kernel framebuffer support in most cases.
--
Andrew C. Aitchison Cambridge
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