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    SubjectRe: Weird PCI problem

    On Sat, 17 Apr 1999, Rogier Wolff wrote:

    > Gerard Roudier wrote:
    > > If you can do that, then, I will recommend you to do at least:
    > >
    > > - Read this base address register
    > > - Warn if any of bit 1, 2 or 3 is set.
    > > - Mask all the bits that should have read zero (bit 0,1,2,3)
    > > - Rewrite this base address register
    > > - Read it again and warn if any bit 0, 1, 2 or 3 is still set.
    > In my opinion that last one should be "bail out if any of the
    > addressing type bits is still set".

    Indeed. It was just a minimal recommendation against just silently trying
    to clear the offending bits. I didn't encourage to let the driver blindly
    attach the device and tamper the address as a memory mapped address.
    I obviously assumed this not to happen if the last read of the bits
    returned wrong values.

    > The PLX (which I understand is the PCI bridge for the card) is capable
    > of mapping stuff into IO space as well as into memory space. It will
    > simply do whatever the bit is set at. You're supposed to program the
    > eeprom in such a way that the bit becomes read-only, but it is
    > certainly writeable in hardware, and the device will honour whatever
    > it is set at.
    > Telling the chip you want a 64k IOmapped window is probably going to
    > crash the machine sooner or later.

    If this window does not conflict and no driver will tamper the window and
    the chip hasn't exploded at the time this bit 0 has been set, then nothing
    bad should happen when attempting to clear this bit 0, in my opinion. :-)


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