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Date:   Thu, 3 Nov 2022 12:06:15 +0000
From:   Cristian Marussi <cristian.marussi@arm.com>
To:     Sudeep Holla <sudeep.holla@arm.com>
Cc:     Florian Fainelli <f.fainelli@gmail.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        james.quinlan@broadcom.com, Jonathan.Cameron@huawei.com,
        etienne.carriere@linaro.org, vincent.guittot@linaro.org,
        souvik.chakravarty@arm.com, wleavitt@marvell.com,
        peter.hilber@opensynergy.com, nicola.mazzucato@arm.com,
        tarek.el-sherbiny@arm.com, quic_kshivnan@quicinc.com
Subject: Re: [PATCH v4 0/11] Introduce a unified API for SCMI Server testing
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On Thu, Nov 03, 2022 at 11:21:47AM +0000, Sudeep Holla wrote:
> On Fri, Oct 28, 2022 at 07:38:25PM -0700, Florian Fainelli wrote:
> > Hi Christian,
> > 
> > On 10/19/2022 1:46 PM, Cristian Marussi wrote:
> > [snip]
> > 
> > > In V2 the runtime enable/disable switching capability has been removed
> > > (for now) since still not deemed to be stable/reliable enough: as a
> > > consequence when SCMI Raw support is compiled in, the regular SCMI stack
> > > drivers are now inhibited permanently for that Kernel.
> > 
> > For our platforms (ARCH_BRCMSTB) we would need to have the ability to start
> > with the regular SCMI stack to satisfy if nothing else, all clock consumers
> > otherwise it makes it fairly challenging for us to boot to a prompt as we
> > purposely turn off all unnecessary peripherals to conserve power. We could
> > introduce a "full on" mode to remove the clock provider dependency, but I
> > suspect others on "real" silicon may suffer from the same short comings.
> >
> 
> Fair enough. But if we are doing SCMI firmware testing or conformance via
> the $subject proposed way, can these drivers survive if the userspace do
> a random or a torture test changing the clock configurations ? Not sure
> how to deal with that as the intention here is to do the testing from the
> user-space and anything can happen. How do we avoid bring the entire system
> down while doing this testing. Can we unbind all the drivers using scmi on
> your platform ? I guess no. Let me know.
> 
> > Once user-space is reached, I suppose we could find a way to unbind from all
> > SCMI consumers, and/or ensure that runtime PM is disabled, cpufreq is in a
> > governor that won't do any active frequency switching etc.
> >
> > What do you think?
> 
> Yes, Cristian always wanted to support that but I am the one trying to
> convince him not to unless there is a strong requirement for it. You seem
> to suggest that you have such a requirement, but that just opens loads of
> questions and how to we deal with that. Few of them are as stated above, I
> need to recall all the conversations I had with Cristian around that and why
> handling it may be bit complex.

:D ... I really even more like the idea of enabling on demand full coexistence
so that I completely delegate to the users to manually deal with possible
interferences at runtime and drop any liabilities if someone shoots himself
in the foot :P

... jokes apart I'll post today a V5 with a few fixes and and an optional
coexistence mode so that Florian can experiment and see how much is feasible
to operate in this way by manually unbinding/re-configuring SCMI behaviour
at runtime before starting tests and not kill the system on something
like ARCH_BRCMSTB platforms.

Thanks,
Cristian