Re: [PATCH] PM-Timer: doesn't use workaround if chipset is not buggy

[Andreas Mohr]

Hi,

On Thu, Mar 23, 2006 at 03:49:18AM +0900, OGAWA Hirofumi wrote:
> This patch adds blacklist of buggy chip, and if chip is not buggy,
> this uses fast normal version instead of slow workaround version.

Nice!
Testing on ICH5 (P4HT) hasn't shown any problems so far.

> If chip is buggy, warnings "pmtmr is slow". But sounds like there is
> gray zone. I found the PIIX4 errata, but I couldn't find the ICH4
> errata.  But some motherboard seems to have problem.

Same here, the ICH4 trace is nowhere to be found.

Should I do a public request for chipset testing?
(I wrote a small test app here that would hopefully identify a buggy
chipset).

Data that I have collected from internet snippets (mostly Intel errata
documents):
Affected (PCI ID / rev):
  - ICH4???
  - PIIX4 A0 (0x7113 / 00?), A1 (0x7113 / 00?), B0 (0x7113 / 01?)
  - PIIX4E A0 (0x7113 / 02?)
Probably fixed (PCI ID / rev):
  - PIIX4M A0 (0x7113 / 03?)

My Toshiba Satellite 4280 seems to have non-buggy PIIX4M
(since it's PCI rev. 03), haven't had time to test reliability yet, though.

> So, if found a ICH4, also warnings, and uses a workaround version.  If
> user's ICH4 is good actually, user can specify the "pmtmr_good" boot
> parameter to use fast version.

Good, that's how it should be done as long as it's not entirely known which
chipsets (both Intel and possibly also non-Intel!) are buggy.

Also, I think that since triple-reading wastes 3% of system time, it would
be very nice to be able to eventually write a software workaround for buggy
systems, too.
This could perhaps be done by keeping the *old* value in a global yet
thread-safe variable and checking whether the new value is safely related
to it if within short jiffies distance (but since jiffies are probably
calculated from pmtmr readings... :-P).

Andreas Mohr
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