linux-kernel - Re: [PATCH V2 1/2] firmware: arm_scmi: Ensure that the message-id supports fastchannel

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Message-ID: <ZthU36Qkzwa5Ilrb@bogus>
Date: Wed, 4 Sep 2024 13:38:55 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Konrad Dybcio <konradybcio@...nel.org>
Cc: Johan Hovold <johan@...nel.org>, Sibi Sankar <quic_sibis@...cinc.com>,
	cristian.marussi@....com, linux-kernel@...r.kernel.org,
	arm-scmi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-arm-msm@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH V2 1/2] firmware: arm_scmi: Ensure that the message-id
 supports fastchannel

On Wed, Sep 04, 2024 at 01:29:29PM +0200, Konrad Dybcio wrote:
> On 4.09.2024 9:00 AM, Johan Hovold wrote:

[...]

> >
> > Unfortunately, this patch breaks resume from suspend on the x1e80100 crd:
> >
> >         [   26.919676] CPU4: Booted secondary processor 0x0000010000 [0x511f0011]
> >         [   26.960607] arm-scmi firmware:scmi: timed out in resp(caller: do_xfer+0x164/0x568)
> >         [   26.987142] cpufreq: cpufreq_online: ->get() failed
> >
> > and then the machine hangs (mostly, I saw an nvme timeout message after a
> > while).
> >
> > Make sure you test suspend as well as some of the warnings I reported
> > only show up during suspend.
>
> Eh it looks like PERF_LEVEL_GET (msgid 8) requires the use of FC, but
> the firmware fails to inform us about it through BIT(0) in attrs..
>

Just trying to understand things better here. So the firmware expects OSPM
to just use FC only for PERF_LEVEL_GET and hence doesn't implement the
default/normal channel for PERF_LEVEL_GET(I assume it returns error ?)
but fails to set the attribute indicating FC is available for the domain.

I am not sure if that is stupid choice or there is some cost benefit in
not implementing PERF_LEVEL_GET via normal channel if that is a fact. I
am very much interested to know the reason either way especially if it
is latter.

--
Regards,
Sudeep