linux-kernel - Re: [PATCH v24 3/7] soc: mediatek: SVS: introduce MTK SVS engine

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Date:   Wed, 20 Apr 2022 17:06:33 -0700
From:   Kevin Hilman <khilman@...nel.org>
To:     Roger Lu <roger.lu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Enric Balletbo Serra <eballetbo@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Nicolas Boichat <drinkcat@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Fan Chen <fan.chen@...iatek.com>,
        HenryC Chen <HenryC.Chen@...iatek.com>,
        Xiaoqing Liu <Xiaoqing.Liu@...iatek.com>,
        Charles Yang <Charles.Yang@...iatek.com>,
        Angus Lin <Angus.Lin@...iatek.com>,
        Mark Rutland <mark.rutland@....com>,
        Nishanth Menon <nm@...com>, Roger Lu <roger.lu@...iatek.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com,
        Guenter Roeck <linux@...ck-us.net>,
        Jia-wei Chang <jia-wei.chang@...iatek.com>
Subject: Re: [PATCH v24 3/7] soc: mediatek: SVS: introduce MTK SVS engine

Hi Roger,

Roger Lu <roger.lu@...iatek.com> writes:

> The Smart Voltage Scaling(SVS) engine is a piece of hardware
> which calculates suitable SVS bank voltages to OPP voltage table.
> Then, DVFS driver could apply those SVS bank voltages to PMIC/Buck
> when receiving OPP_EVENT_ADJUST_VOLTAGE.
>
> Signed-off-by: Roger Lu <roger.lu@...iatek.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

Can SVS work with one or the other clusters disabled?  It seems like it
should still be able to work.  However, if you disable the 2nd cluster
(e.g. by passing `maxcpus=4` on the kernel command-line, the SVS driver
will fail to probe.

I dont' think it's a blocker for merging this series, but making the
probe a bit more robust so it can handle the cluster being disabled
would be nice additional fix for later.

For example, upstream kernel on mt8183-pumpkin board is very unstable
with the 2nd cluster enabled (I'm still trying to debug why), but I have
to boot with `maxcpus=4` on the cmdline, otherwise kernel fails to boot,
so that's how I noticed this probe failure with SVS.

Kevin