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From:   Kevin Hilman <khilman@baylibre.com>
To:     Rex-BC Chen <rex-bc.chen@mediatek.com>, rafael@kernel.org,
        viresh.kumar@linaro.org, robh+dt@kernel.org, krzk+dt@kernel.org,
        matthias.bgg@gmail.com
Cc:     jia-wei.chang@mediatek.com, roger.lu@mediatek.com,
        hsinyi@google.com, angelogioacchino.delregno@collabora.com,
        linux-pm@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org,
        Project_Global_Chrome_Upstream_Group@mediatek.com,
        Rex-BC Chen <rex-bc.chen@mediatek.com>
Subject: Re: [PATCH V3 11/15] cpufreq: mediatek: Link CCI device to CPU
In-Reply-To: <20220415055916.28350-12-rex-bc.chen@mediatek.com>
References: <20220415055916.28350-1-rex-bc.chen@mediatek.com>
 <20220415055916.28350-12-rex-bc.chen@mediatek.com>
Date:   Wed, 20 Apr 2022 11:09:59 -0700
Message-ID: <7hv8v3eidk.fsf@baylibre.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Hi Rex,

Rex-BC Chen <rex-bc.chen@mediatek.com> writes:

> From: Jia-Wei Chang <jia-wei.chang@mediatek.com>
>
> In some MediaTek SoCs, like MT8183, CPU and CCI share the same power
> supplies. Cpufreq needs to check if CCI devfreq exists and wait until
> CCI devfreq ready before scaling frequency.
>
> Before CCI devfreq is ready, we record the voltage when booting to
> kernel and use the max(cpu target voltage, booting voltage) to
> prevent cpufreq adjust to the lower voltage which will cause the CCI
> crash because of high frequency and low voltage.
>
> - Add is_ccifreq_ready() to link CCI device to CPI, and CPU will start
>   DVFS when CCI is ready.
> - Add platform data for MT8183.
>
> Signed-off-by: Jia-Wei Chang <jia-wei.chang@mediatek.com>
> Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>

The solution of keeping the max of the CPU voltage from OPP and boot-up
voltage makes sense until CCI is ready.  Thank you for the rework and
the detailed technical explanations.

Reviewed-by: Kevin Hilman <khilman@baylibre.com>

Kevin