Re: [PATCH] powerpc/pseries/vas: Don't print an error when VAS is unavailable

Haren Myneni [off-list ref] writes:

On Tue, 2021-11-30 at 10:25 +1100, Michael Ellerman wrote:

quoted

Nicholas Piggin [off-list ref] writes:

quoted

Excerpts from Cédric Le Goater's message of November 26, 2021 5:13
pm:

quoted

On 11/26/21 06:21, Nicholas Piggin wrote:

quoted

KVM does not support VAS so guests always print a useless error
on boot

     vas: HCALL(398) error -2, query_type 0, result buffer
0x57f2000

Change this to only print the message if the error is not
H_FUNCTION.

Just being curious, why is it even called since "ibm,compression"
should
not be exposed in the DT ?

It looks like vas does not test for it. I guess in theory there can
be 
other functions than compression implemented as an accelerator.
Maybe
that's why?

Yeah I guess, or it's just not structured that well. The vas platform
code is a bit awkward, it's there to support drivers, but it's not
actually driver code.

I think we can probably rework it so the vas code does nothing until
a
driver calls in to it.

eg. something like below.

Correct, Even though NXGZIP is the only usage right now, VAS is
accelerator switchboard which should support other coprocessor types
such as GZIP and 842 or SW type solutions such as fast thread wakeup
and fast memory copy. 

So can we leave VAS initialization separate from drivers and use some
feature such as FW_FEATURE_LPAR to differentiate from KVM guests?

FW_FEATURE_LPAR is true on KVM guests as well.

As Tyrel pointed out, you should be looking for "hcall-vas" in
"ibm,hypertas-functions" and setting a new FW_FEATURE_VAS based on that.
Then use that to gate the vas init routine.

cheers