linux-kernel - Re: [PATCH v4 1/4] firmware: arm_scmi: Add polling support for completion in smc

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Date:   Tue, 3 Oct 2023 11:33:17 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Nikunj Kela <quic_nkela@...cinc.com>
Cc:     cristian.marussi@....com, robh+dt@...nel.org,
        Sudeep Holla <sudeep.holla@....com>,
        Brian Masney <bmasney@...hat.com>,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        andersson@...nel.org, konrad.dybcio@...aro.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 1/4] firmware: arm_scmi: Add polling support for
 completion in smc

On Mon, Sep 11, 2023 at 12:43:56PM -0700, Nikunj Kela wrote:
> Currently, the return from the smc call assumes the completion of
> the scmi request. However this may not be true in virtual platforms
> that are using hvc doorbell.
>

Hmm, it is expectation from SMCCC for the fast calls. Is you HVC FID
not a fast call. AFAIK, only TOS use yielding calls. Are you using them
here ? If not, this must complete when the SMC/HVC returns. We added
support for platforms indicating the same via interrupt.

I would like to avoid adding this build config. Why does it require polling ?
Broken firmware ? I would add a compatible for that. Or if the qcom always
wants to do this way, just make it specific to the qcom compatible.

I would avoid a config flag as it needs to be always enabled for single
image and affects other platforms as well. So please drop this change.
If this is absolutely needed, just add additional property which DT
maintainers may not like as it is more like a policy or just make it
compatible specific.

--
Regards,
Sudeep