Messages in this thread | | | Date | Sun, 30 Dec 2007 17:07:51 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override |
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* Rene Herman <rene.herman@keyaccess.nl> wrote:
> On 30-12-07 16:28, Ingo Molnar wrote: > >> Reading from the 0x3cc port does not impact the cursor position update >> sequence IIRC - i think the vidport is even ignored for the input >> direction by most hardware, there's a separate input register. The 0x3cc >> port is a well-defined VGA register which should be unused on non-VGA >> hardware. (which makes it a perfect delay register in any case) > > Hardly. Duron 1300 on AMD756:
but that does not matter at all: that's not '90s era hardware that we are (slightly) worried about wrt. IO delays in misc_32.c. (i.e. on _real_ ISA systems)
> rene@7ixe4:~/src/port80$ su -c ./port80 > cycles: out 2400, in 2401 > rene@7ixe4:~/src/port80$ su -c ./port3cc > cycles: out 459, in 394
of course, since VGA is implemented in the southbridge or on the video card, so it's much faster than a true ISA cycle.
the only (minor) worry we have here is really ancient systems relying on delays there. Modern VGA hardware most definitely does not need any such delays.
Ingo
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