Gautham R Shenoy [off-list ref] writes:

Hi Michael,

On Wed, Dec 06, 2017 at 09:54:27PM +1100, Michael Ellerman wrote:

quoted

Shilpasri G Bhat [off-list ref] writes:

quoted

From: "Gautham R. Shenoy" <redacted>

Pstates are 8bit values but on POWER8 they are negative and on POWER9
they are positive. This patch adds helper routines to differentiate
the sign to read the correct pstate value.

This sounds like it could be a bad bug, but I can't really tell from the
change log. What is the actual impact of not having this patch?

On some POWER9 platforms, there can be more than 128 pstates. 

Without this patch, on such platforms, if the value of the current
frequency corresponds to a pstate greater than 128, then the code will
interpret it as a negative number, and report that the "pstate is out
of bound" while returning a nominal frequency.

OK, that's good detail to have in the change log, please include it.

quoted

Should it have a Fixes/Cc-stable tag?

This doesn't fix any prior commit, but is fixes a newly discovered
bug.

OK. You could say it "fixes" the commit that added Power9 support to the
driver, but it seems there wasn't really a commit that did that
specifically.

I will resend the patch Cc'ing stable.

You don't have to Cc stable, that was just a suggestion. Though it
sounds like the symptoms are probably bad enough to warrant it.

cheers