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    SubjectRe: [PATCH] x86: provide a DMI based port 0x80 I/O delay override
    Juergen Beisert wrote:
    > On Sunday 30 December 2007 16:38, Alan Cox wrote:
    >>> do you have any memories about the outb_p() use of misc_32.c:
    >>>
    >>> pos = (x + cols * y) * 2; /* Update cursor position */
    >>> outb_p(14, vidport);
    >>> outb_p(0xff & (pos >> 9), vidport+1);
    >>> outb_p(15, vidport);
    >>> outb_p(0xff & (pos >> 1), vidport+1);
    >>>
    >>> was this ever needed? This is so early in the bootup that can we cannot
    >> None - but we don't care.
    >
    > Was this embedded outb to 0x80 for delay only? Maybe I'm wrong. But in the
    > case above it forces the chipselect signal to deselect the hardware between
    > the access to vidport and vidport+1. Some devices need this to latch the
    > values correctly. Otherwise the chipselect signal would be active for all
    > four accesses in the example above (and only data and addresses are changing
    > from device's view).
    >

    Presumably you're talking about an actual ISA bus here. On those, you
    don't really have a chip select; but you'd expect the latch to happen on
    the rising edge of IOW#, not on an internally generated chip select.

    Now, I think there is a specific reason to believe that EGA/VGA (but
    perhaps not CGA/MDA) didn't need these kinds of hacks: the video cards
    of the day was touched, directly, by an interminable number of DOS
    applications. CGA/MDA generally *were not*, due to the unsynchronized
    memory of the original versions (writing could cause snow), so most
    applications tended to fall back to using the BIOS access methods for
    CGA and MDA.

    -hpa


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