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From:   Kevin Hilman <khilman@kernel.org>
To:     Roger Lu <roger.lu@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Enric Balletbo Serra <eballetbo@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Nicolas Boichat <drinkcat@google.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Philipp Zabel <p.zabel@pengutronix.de>
Cc:     Fan Chen <fan.chen@mediatek.com>,
        HenryC Chen <HenryC.Chen@mediatek.com>,
        Xiaoqing Liu <Xiaoqing.Liu@mediatek.com>,
        Charles Yang <Charles.Yang@mediatek.com>,
        Angus Lin <Angus.Lin@mediatek.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Nishanth Menon <nm@ti.com>, Roger Lu <roger.lu@mediatek.com>,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org,
        Project_Global_Chrome_Upstream_Group@mediatek.com,
        Guenter Roeck <linux@roeck-us.net>,
        Jia-wei Chang <jia-wei.chang@mediatek.com>
Subject: Re: [PATCH v24 3/7] soc: mediatek: SVS: introduce MTK SVS engine
In-Reply-To: <20220420102044.10832-4-roger.lu@mediatek.com>
References: <20220420102044.10832-1-roger.lu@mediatek.com>
 <20220420102044.10832-4-roger.lu@mediatek.com>
Date:   Wed, 20 Apr 2022 17:06:33 -0700
Message-ID: <7h5yn3s3jq.fsf@baylibre.com>
MIME-Version: 1.0
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Hi Roger,


Roger Lu <roger.lu@mediatek.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@mediatek.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.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