Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux