Re: explanation of hackvideo patch to proc.c?

[Aivils <ai...@un...>]

> I'm working on a problem where I need to be able to have multiple X
> servers responding concurrently (the video driver is not actually
> writing to a framebuffer device), and so I was trying out
> the /proc/bus/pci/hackvideo patch provided by linuxconsole/ruby.  It
> does not seem to solve my problem, but I would like to understand what
> it is supposed to do (to hopefully give me better insight into where my
> problem is).  I believe the following code in proc_bus_pci_write() in
> drivers/pci/proc.c is the only modification to the 2.6 kernel code
> (other than reading & writing the proc entry) for the hackvideo patch:
>
> if (pci_hackvideo && (pos == PCI_CMD_STAT_REG) &&

pos - position to write

>            (buf[0] <= PCI_CMD_MASTER_ENABLE) &&

buf[0] - data to write

>             ((dev->class>>8) == 0x0300 ||
>              (dev->class>>8) == 0x0400 ||
>              (dev->class>>8) == 0x0000   ) )

dev->class -  is video adapter PCI device class

>                 return -EINVAL;
>
> It is not clear to me what this code is doing, however. 

xf86 cannot write PCI disable command in to device I/O port. 

> Can anyone 
> offer an explanation? 

http://startx.times.lv/eng-xf.html

> Does it relate to XFree86's disabling of port I/O 
> access when switching VTs?  If so, is it designed to block the
> functionality of a particular function called within xf86VTSwitch() in
> xc/programs/Xserver/hw/xfree86/common/xf86Events.c?

I do not know. This patch disallow pciIoAccessDisable() normal work (file: 
xc/programs/Xserver/hw/xfree86/common/xf86pciBus.c) and other pci*Disable() 
funcs will not work normal.
xf86 will use Linux /proc interface with this config:
Section "ServerFlags"
Option "PciOsConfig" "1"
EndSection

Practice.
Nvidia closed source drivers version 1.0-2880 - 1.0-4496 will hung up system, 
when xf86 on AGP video adapter restart. Now, recent 1.0-5336 works very well,
seems this is lucky case.(2.4.25, xfree4.3.0-7mdk)
Almost AGP xf86 restart will hung up system, when /proc/bus/pci/hackvideo 
used. You can use xf86 without restart :)

Aivils Stoss