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

H. Peter Anvin wrote:

David P. Reed wrote:

As support: port 80 on the reporter's (my) HP dv9000z laptop clearly responds to reads differently than "unused" ports. In particular, an inb takes 1/2 the elapsed time compared to a read to "known" unused port 0xed - 792 tsc ticks for port 80 compared to about 1450 tsc ticks for port 0xed and other unused ports (tsc at 800 MHz).

Any timings for port 0xf0 (write zero), out of curiosity?

Here's a bunch of data:

port 0xF0: cycles: out 919, in 933
port 0xed: cycles: out 2541, in 2036
port 0x70: cycles: out n/a,  in 934
port 0x80: cycles: out 1424, in 795

AMD Turion 64x2 TL-60 CPU running at 800 MHz, nVidia MCP51 chipset, Quanta motherboard. Running 2.6.24-rc5 with Ingo's patch so inb_p, etc. use port 0xed.

Note that I can run the port 80 test once, the second time I get the hard freeze. I didn't try writing to port 70 from userspace - that one's dangerous, but the reading of it was included for a timing typical of a chipset supported device. These are all pretty consistent.

I find the "read" timing from 0x80 verrrrry interesting. The write timeing is also interesting, being faster than an unused port.

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