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

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Date:   Mon, 26 Sep 2022 11:00:26 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chen-Yu Tsai <wenst@...omium.org>
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

Il 26/09/22 10:57, Chen-Yu Tsai ha scritto:
> 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?
> 
> 

Yeah, sure! I'll send a new version most probably today.
Thanks for the review(s)!

Cheers,
Angelo

> 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
>>>>
>>
>>