Re: [PATCH] powerpc/pseries: delete scanlog

[Nathan Lynch <nathanl@linux.ibm.com>]

Michael Ellerman <mpe@ellerman.id.au> writes:

> Nathan Lynch <nathanl@linux.ibm.com> writes:
>> Nathan Lynch <nathanl@linux.ibm.com> writes:
>>> Remove the pseries scanlog driver.
>>>
>>> This code supports functions from Power4-era servers that are not present
>>> on targets currently supported by arch/powerpc. System manuals from this
>>> time have this description:
>>>
>>>   Scan Dump data is a set of chip data that the service processor gathers
>>>   after a system malfunction. It consists of chip scan rings, chip trace
>>>   arrays, and Scan COM (SCOM) registers. This data is stored in the
>>>   scan-log partition of the system’s Nonvolatile Random Access
>>>   Memory (NVRAM).
>>>
>>> PowerVM partition firmware development doesn't recognize the associated
>>> function call or property, and they don't see any references to them in
>>> their codebase. It seems to have been specific to non-virtualized
>>> pseries.
>>
>> Just bumping this to see if there are any objections.
>
> Not an objection, I like nothing better than dropping old unused cruft,
> but are we sure it's safe to remove the proc file?
>
> I see that rtas_errd still looks for it, have you checked that it will
> handle the absence of the file gracefully and continue doing whatever
> else it does?

Uhh. I will stop forgetting to check ppc64_diag when making such
changes. Thanks for pointing this out.

> On further inspection it looks like the code that looks for it in
> rtas_errd is #if 0'ed out (??), so maybe it's dead.

Yes it seems so. From rtas_errd's main():

#if 0
	/* 
	 * Check to see if a new scanlog dump is available;  if so, copy it to
	 * the filesystem and associate the dump with the first error processed.
	 */
	check_scanlog_dump();
#endif

And that's the only entry point into the code that collects the scanlog
data. And that dead code appears to deal with the absence of
/proc/ppc64/scan-log-dump gracefully. It has been like that since
initial git import in 2013.

> Anyway if you can test that rtas_errd still works that'd be good.

I've verified that it starts normally and logs EPOW events associated
with partition migration.

> Presumably there's no other code that cares about the proc file.

AFAIK this is right. powerpc-utils and librtas do not use it. librtas
has a wrapper for the calling the associated RTAS function directly, but
that's fine.

I tried using GitHub's search to find instances of "scan-log-dump" that
weren't from Linux or ppc64_diag (need to be logged in I think):

https://github.com/search?q=%22scan-log-dump%22+-path%3Aarch%2Fpowerpc+-filename%3Ascanlog.c+-extension%3Apatch&type=Code&ref=advsearch&l=&l=

This hasn't yielded any unexpected users. There may be better search
terms but that's what a few minutes of fiddling with it got me.