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

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Date:   Mon, 26 Sep 2022 10:36:29 +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 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 :-)

>> 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
>>