On Tue, 25 Feb 2003, Mark Vojkovich wrote:
> > >> While tracking down a bug, I encoutered these functions in:
> > >> programs/Xserver/hw/xfree86/vgahw/vgaHW.c:
> > >> void vgaHWLock(vgaHWPtr hwp)
> > >> {
> > >> /* Protect CRTC[0-7] */
> > >> hwp->writeCrtc(hwp, 0x11, hwp->readCrtc(hwp, 0x11) & ~0x80);
> > >> }
> > >> void vgaHWUnlock(vgaHWPtr hwp)
> > >> {
> > >> /* Unprotect CRTC[0-7] */
> > >> hwp->writeCrtc(hwp, 0x11, hwp->readCrtc(hwp, 0x11) | 0x80);
> > >> }
> > >> Every reference I can find on the sbuject, (specifically Ferraro's book,
> > >> 3rd ed, along with many HTML references) indicate that this logic is
> > >> reversed. That is, for CRTC reg 0x11 bit 7: 1=disable, 0=enable writing
> > >> to CRTC regs[0-7].
> > >> Comments?
> > >You are absolutely correct. I've just committed a change to correct this.
> > >Thanks for pointing out the problem.
> > I wonder why this hasn't shown up as a problem anywhere?
> The "nv" driver doesn't use these. It provides its own which
> has the reverse logic from what vgaHW was using.
Well, the bit doesn't affect reading the registers. As for writes,
vgaHWRestoreMode(), which many drivers end up calling to set a mode,
ensures the bit is off before re-writting the CRTC registers.
Marc.
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