linux-kernel - Re: [PATCH v2 4/4] clk: mediatek: mt8183: Add clk mux notifier for MFG mux

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Date:   Mon, 23 May 2022 12:05:20 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chen-Yu Tsai <wenst@...omium.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Chun-Jie Chen <chun-jie.chen@...iatek.com>,
        Miles Chen <miles.chen@...iatek.com>,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] clk: mediatek: mt8183: Add clk mux notifier for
 MFG mux

Il 23/05/22 10:59, Chen-Yu Tsai ha scritto:
> When the MFG PLL clock, which is upstream of the MFG clock, is changed,
> the downstream clock and consumers need to be switched away from the PLL
> over to a stable clock to avoid glitches.
> 
> This is done through the use of the newly added clk mux notifier. The
> notifier is set on the mux itself instead of the upstream PLL, but in
> practice this works, as the rate change notifitcations are propogated
> throughout the sub-tree hanging off the PLL. Just before rate changes,
> the MFG mux is temporarily and transparently switched to the 26 MHz
> main crystal. After the rate change, the mux is switched back.
> 
> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>