Re: More info on port 80 symptoms on MCP51 machine.

Rene Herman
2007-12-12T20:27:44Z

On 12-12-07 21:07, David P. Reed wrote:

> Sadly, I've been busy with other crises in my day job for the last few
> days. I did modify Rene's test program and ran it on my "problem"
> machine, with the results below.
>
> The interesting part of this is that port 80 seems to respond to "in"
> instructions faster than the presumably "unused" ports 0xEC and 0XEF
> (those were mentioned by someone as alternatives to port 80).

Don't know if someone else mentioned those but I only said 0xed. That's the
value Phoenix BIOSes use (yes, and which H. Peter Anvin) reported as being
generally problematic as well).

It's in fact not all that unexpected it seems that port 0x80 responds to in
given that it's used by the DMA controller. It's a write that falls on deaf
ears. The read is going to be faster if it doesn't timeout on an unused port.

Although it's not faster for everyone, such as for me indicating that for us
port 0x80 is really-really unused, it is for many. See results here:

http://lkml.org/lkml/2007/12/12/309

> That, and the fact that the port 80 test reliably freezes the machine
> solid the second time it is run, and the "hwclock" utility reliably
> hangs the machine if the port 80's are used in the CMOS_READ/CMOS_WRITE
> loop, seems to strongly indicate that this chipset or motherboard
> actually uses port 80, rather than there being a bus problem.

Yes, so it seems. In this case we could in fact also "fix" your situation by
just going to 0xed depending on for example DMI. Alan Cox just posted a few
further problems with a simple udelay() replacement...

> Someone might have an in to nVidia to clarify this, since I don't. In
> any case, the udelay(2) approach seems to be a safe fix for this machine.
>
> Hope input from an "outsider" is helpful in going forward. I put a lot
> of time and effort into tracking down this problem on this particular
> machine model, largely because I like the machine.
>
> Running the (slightly modified to test ports 80, ec, ef instead of just
> port 80) test when the 2 GHz max speed CPU is running at 800 MHz, here's
> what I get for port 80 and port ec and port ef.
>
> port 80: cycles: out 1430, in 792

At 800 MHz, that's 1.79 / 0.99 microseconds. The precision of the "in" is
somewhat interesting. Did someone at nVidia think it's an "in" from 0x80
which should get the 1 microsec delay?

> port ef: cycles: out 1431, in 1378
> port ec: cycles: out 1432, in 1372

Unused ports, bus timeouts.

> ----------------------------
>
> System info: HP Pavilion dv9000z laptop (AMD64x2)
>
> PCI bus controller is nVidia MCP51.
> processor : 0
> vendor_id : AuthenticAMD
> cpu family : 15
> model : 72
> model name : AMD Turion(tm) 64 X2 Mobile Technology TL-60
> stepping : 2
> cpu MHz : 800.000
> cache size : 512 KB

Rene.