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

[Ingo Molnar]

* Rene Herman <rene.herman@xxxxxxxxxxxx> 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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