linux-kernel - Re: [PATCH 2/2] clk: mediatek: mt8195-topckgen: Refactor parents for top

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Message-ID: <59a88e00-0758-32b8-7ce4-8dea84a9b0f7@baylibre.com>
Date:   Tue, 18 Jul 2023 10:37:13 +0200
From:   Alexandre Mergnat <amergnat@...libre.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Maxime Ripard <mripard@...nel.org>
Cc:     Chen-Yu Tsai <wenst@...omium.org>, sboyd@...nel.org,
        mturquette@...libre.com, matthias.bgg@...il.com, msp@...libre.com,
        yangyingliang@...wei.com, u.kleine-koenig@...gutronix.de,
        miles.chen@...iatek.com, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH 2/2] clk: mediatek: mt8195-topckgen: Refactor parents for
 top_dp/edp muxes



On 17/07/2023 16:30, AngeloGioacchino Del Regno wrote:
>>>>> However I'm not sure if that works for parents. It should, given the
>>>>> original use case was for the sunxi platforms, which like the MediaTek
>>>>> platform here has 2 PLLs for video related consumers, but I couldn't
>>>>> find code verifying it.
>>>>
>>>> If you want to prevent clocks from ever being reparented, you can use
>>>> the new clk_hw_determine_rate_no_reparent() determine_rate
>>>> implementation.
>>>>
>>>
>>> We want the clocks to be reparented, as we need them to switch 
>>> parents as
>>> explained before... that's more or less how the tree looks:
>>>
>>> TVDPLL(x) -> PLL Divider (fixed) -> MUX -> Gate -> Controller
>>>
>>> Besides, I think that forcing *one* parent to the dp/edp mux would 
>>> produce a
>>> loss of the flexibility that the clock framework provides.
>>>
>>> I again want to emphasize on the fact that TVDPLL1 and TVDPLL2 are 
>>> *identical*
>>> in specs, and on that there will never be a MT8195 SoC that has only 
>>> one of
>>> the two PLLs, for obvious reasons...
>>>
>>> P.S.: If you need more context, I'll be glad to answer to any other 
>>> question!
>>
>> Then I have no idea what the question is :)
>>
>> What are you trying to achieve / fix, and how can I help you ? :)
>>
> 
> Chen-Yu, Alexandre had/have questions about if there was any other 
> solution instead
> of using the solution of *this* commit, so, if there's any other better 
> solution
> than the one that I've sent as this commit.
> 
> I'm the one saying that this commit is the best solution :-P

Hi Angelo,

My solution is based on PLL static allocation, because I missed it could 
be reparented actually. I think I've a better understanding of this 
commit now, thanks to your explanations. Looks fine for me.

Reviewed-by: Alexandre Mergnat <amergnat@...libre.com>

-- 
Regards,
Alexandre