linux-kernel - Re: [PATCH v2 05/10] clk: mediatek: clk-mt8195-mfg: Reparent mfg

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Message-ID: <CAGXv+5HYKjDJALa6MAAE4XzRTMfE_vdEWg6XaWekUq7w8ko3BQ@mail.gmail.com>
Date:   Mon, 26 Sep 2022 16:57:17 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     matthias.bgg@...il.com, mturquette@...libre.com, sboyd@...nel.org,
        miles.chen@...iatek.com, rex-bc.chen@...iatek.com,
        nfraprado@...labora.com, chun-jie.chen@...iatek.com,
        jose.exposito89@...il.com, drinkcat@...omium.org,
        weiyi.lu@...iatek.com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org
Subject: Re: [PATCH v2 05/10] clk: mediatek: clk-mt8195-mfg: Reparent mfg_bg3d
 and propagate rate changes

On Mon, Sep 26, 2022 at 4:36 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Il 26/09/22 05:27, Chen-Yu Tsai ha scritto:
> > On Thu, Sep 15, 2022 at 3:25 PM AngeloGioacchino Del Regno
> > <angelogioacchino.delregno@...labora.com> wrote:
> >>
> >> The MFG_BG3D is a gate to enable/disable clock output to the GPU,
> >> but the actual output is decided by multiple muxes; in particular:
> >> mfg_ck_fast_ref muxes between "slow" (top_mfg_core_tmp) and
> >> "fast" (MFGPLL) clock, while top_mfg_core_tmp muxes between the
> >> 26MHz clock and various system PLLs.
> >>
> >> This also implies that "top_mfg_core_tmp" is a parent of the
> >> "mfg_ck_fast_ref" mux (and not vice-versa), so reparent the
> >
> > I don't see where this was the case though? I think what you meant
> > was that the direct parent for "mfg_bg3d" is "mfg_ck_fast_ref, not
> > "top_mfg_core_tmp"?
> >
>
> MFG_BG3D's direct parent is mfg_ck_fast_ref - yes - but in the commit message
> I am explaining how the clock tree for MFG_BG3D really is and, in particular,
> I'm then explaining that:
> * parenting MFG_BG3D to "top_mfg_core_tmp" is wrong; because
> * "top_mfg_core_tmp" is a parent of "mfg_ck_fast_ref" (not the other way around).
>
> So, the question in your comment is addressed just a little later....
>
> >> MFG_BG3D gate to the latter and add the CLK_SET_RATE_PARENT
>
> ...here, where I say "reparent MFG_BG3D to the latter", where "the latter" is,
> exactly "mfg_ck_fast_ref".
>
> I hope you now understand what I am trying to communicate :-)
>
> However, if even after that you still think that the commit description should
> be rewritten in some less tangled and/or more understandable way, I definitely
> can do that.
>
> Please confirm :-)

I think

    This also implies that "top_mfg_core_tmp" is a parent of the
    "mfg_ck_fast_ref" mux (and not vice-versa)

actually confused me.

Maybe just say

    The clock gate comes after all the muxes, so its parent is
    mfg_ck_fast_ref, not top_mfg_core_tmp. Reparent mfg_bg3d to
    the latter to match the hardware ...

Since you are fixing the topology, could you also add a fixes tag?


Thanks
ChenYu


> >> flag to it: this way we ensure propagating rate changes that
> >> are requested on MFG_BG3D along its entire clock tree.
> >>
> >> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> >
> > Otherwise,
> >
> > Reviewed-by: Chen-Yu Tsai <wenst@...omium.org>
> >
> >
> >> ---
> >>   drivers/clk/mediatek/clk-mt8195-mfg.c | 6 ++++--
> >>   1 file changed, 4 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/clk/mediatek/clk-mt8195-mfg.c b/drivers/clk/mediatek/clk-mt8195-mfg.c
> >> index 9411c556a5a9..c94cb71bd9b9 100644
> >> --- a/drivers/clk/mediatek/clk-mt8195-mfg.c
> >> +++ b/drivers/clk/mediatek/clk-mt8195-mfg.c
> >> @@ -17,10 +17,12 @@ static const struct mtk_gate_regs mfg_cg_regs = {
> >>   };
> >>
> >>   #define GATE_MFG(_id, _name, _parent, _shift)                  \
> >> -       GATE_MTK(_id, _name, _parent, &mfg_cg_regs, _shift, &mtk_clk_gate_ops_setclr)
> >> +       GATE_MTK_FLAGS(_id, _name, _parent, &mfg_cg_regs,       \
> >> +                      _shift, &mtk_clk_gate_ops_setclr,        \
> >> +                      CLK_SET_RATE_PARENT)
> >>
> >>   static const struct mtk_gate mfg_clks[] = {
> >> -       GATE_MFG(CLK_MFG_BG3D, "mfg_bg3d", "top_mfg_core_tmp", 0),
> >> +       GATE_MFG(CLK_MFG_BG3D, "mfg_bg3d", "mfg_ck_fast_ref", 0),
> >>   };
> >>
> >>   static const struct mtk_clk_desc mfg_desc = {
> >> --
> >> 2.37.2
> >>
>
>