linux-kernel - Re: [PATCH v2] clk: mediatek: clk-mux: Add .determine

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Date:   Fri, 14 Oct 2022 13:38:37 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     mturquette@...libre.com, matthias.bgg@...il.com,
        angelogioacchino.delregno@...labora.com,
        chun-jie.chen@...iatek.com, miles.chen@...iatek.com,
        wenst@...omium.org, maxime@...no.tech, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] clk: mediatek: clk-mux: Add .determine_rate() callback

Quoting AngeloGioacchino Del Regno (2022-10-11 06:55:48)
> Since commit 262ca38f4b6e ("clk: Stop forwarding clk_rate_requests
> to the parent"), the clk_rate_request is .. as the title says, not
> forwarded anymore to the parent: this produces an issue with the
> MediaTek clock MUX driver during GPU DVFS on MT8195, but not on
> MT8192 or others.
> 
> This is because, differently from others, like MT8192 where all of
> the clocks in the MFG parents tree are of mtk_mux type, but in the
> parent tree of MT8195's MFG clock, we have one mtk_mux clock and
> one (clk framework generic) mux clock, like so:
> 
> names: mfg_bg3d -> mfg_ck_fast_ref -> top_mfg_core_tmp (or) mfgpll
> types: mtk_gate ->      mux        ->     mtk_mux      (or) mtk_pll
> 
> To solve this issue and also keep the GPU DVFS clocks code working
> as expected, wire up a .determine_rate() callback for the mtk_mux
> ops; for that, the standard clk_mux_determine_rate_flags() was used
> as it was possible to.
> 
> This commit was successfully tested on MT6795 Xperia M5, MT8173 Elm,
> MT8192 Spherion and MT8195 Tomato; no regressions were seen.
> 
> For the sake of some more documentation about this issue here's the
> trace of it:
> 

Applied to clk-next