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Date:   Thu, 21 Apr 2022 11:42:43 +0200
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Subject: Re: [RFC PATCH 0/7] clk: mediatek: Move to struct clk_hw provider
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To:     Chen-Yu Tsai <wenst@chromium.org>
Cc:     Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Chun-Jie Chen <chun-jie.chen@mediatek.com>,
        Miles Chen <miles.chen@mediatek.com>,
        Rex-BC Chen <rex-bc.chen@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-clk@vger.kernel.org, linux-mediatek@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
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        <nfraprado@collabora.com>
References: <20220419081246.2546159-1-wenst@chromium.org>
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From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
In-Reply-To: <CAGXv+5G2Uyq5fdMUnhr5wOm6O8M3dHNKGaSP2L_Vv1o28mXmOQ@mail.gmail.com>
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Il 21/04/22 08:05, Chen-Yu Tsai ha scritto:
> On Wed, Apr 20, 2022 at 8:02 PM AngeloGioacchino Del Regno
> <angelogioacchino.delregno@collabora.com> wrote:
>>
>> Il 19/04/22 18:09, Chen-Yu Tsai ha scritto:
>>> On Tue, Apr 19, 2022 at 11:08 PM AngeloGioacchino Del Regno
>>> <angelogioacchino.delregno@collabora.com> wrote:
>>>>
>>>> Il 19/04/22 10:12, Chen-Yu Tsai ha scritto:
>>>>> Hi everyone,
>>>>>
>>>>> This is part 2 of my proposed MediaTek clk driver cleanup work [1].
>>>>>
>>>>
>>>> ..snip..
>>>>
>>>>>
>>>>> The next phase of the cleanup/improvement shall be to introduce some
>>>>> variant of `struct clk_parent_data` to describe clk relationships
>>>>> efficiently.
>>>>>
>>>>> Please have a look.
>>>>>
>>>>
>>>> Hello Chen-Yu,
>>>>
>>>> I am grateful to see this series, as the MediaTek clock drivers are getting
>>>> a bit old, despite new platforms being implemented practically as we speak.
>>>>
>>>> With this, you surely get that I completely agree with the proposed cleanup
>>>> and modernization of the entire MediaTek clocks infrastructure, but I think
>>>> that introducing a `struct clk_parent_data` for these drivers is, at this
>>>> point, a must, that not only fully justifies these patches, but also "makes
>>>> the point" - as the effect of that would be a performance improvement as we
>>>> would *at least* avoid lots of clk_cpy_name() in case of parent_hws, or in
>>>> case or parent_data where no .fw_name is provided (which would be the case
>>>> for most of the clocks).
> 
> BTW, clk_cpy_name() handles const values correctly, i.e. it won't actually
> copy them. The performance issue with using names is the clk core has to
> match them against the ever increasing list of clks in the system to find
> the actual clk object.
> 

Right.

>>> You and me both. :) And yes, one of the intended results is to make the
>>> clk driver probe faster.
>>>
>>>> That said, my advice would be to add that conversion to declaring clocks
>>>> with .hw.init.parent_data and/or .hw.init.parent_hws to this series as to
>>>> really make it complete.
>>>
>>> This series itself already touches a lot of code, even if most of it was
>>> done by coccinelle. I'd like to send them separately to not overwhelm
>>> people.
>>>
>>> Also, I haven't actually started on that part yet. It is actually part 3
>>> of my overall plan. I have a good idea of what to do, given I did similar
>>> work for the sunxi-ng clk drivers (though half finished...).
>>
>> Having a good plan means that you're already half-done though :) :) :)
>>
>> Besides, the reason why I said that you should do the conversion in the same
>> series was exactly because your changes are done with coccinelle scripts...
>> ...but I thought that you already had something in the works for that.
> 
> The final part won't be doable with coccinelle scripts though. It involves
> converting the existing list of clk parent names to IDs. It might be doable
> in Perl or Python, but would likely involve a whole lot of string parsing
> and pattern matching ...
> 

It's going to be a bit tricky, yes... but that's "necessary evil", I guess.

>> Since you still need some time for the final part, having this kind of (even
>> if partial) modernization is still golden.
>> Let's do it in two steps as you prefer then, that's fine for me.
>>
>>>
>>> Most of the clk references are internal to each driver, and those would
>>> be mapped from some CLK_ID to some `struct clk_hw *` internally, but all
>>> blocks have external parents that need to be modeled as well, and we
>>> would likely need global clk name fallbacks for the blocks that don't
>>> have parents declared in the device tree, which is unfortunately most
>>> of them. Especially the central clock controllers like infracfg or pericfg
>>> take many clk inputs, to the point that MediaTek folks were somewhat
>>> unwilling to bloat the device tree with them.
>>>
>>> So it does seem easier to use something like clk_parent_data with
>>> `struct clk_hw *` replaced with an index everywhere. This structure
>>> would get converted into clk_parent_data by the singular clk registration
>>> helpers.
>>>
>>
>> I may not be understanding what you mean by mapping the CLK_ID internally, but
>> from what my brain processed, I think that you want to look at, and basically
>> replicate, how it's done in the Qualcomm clock drivers (and perhaps standardize
>> that in the clock API?).
>>
>> Specifically, clk/qcom/common.h, struct parent_map.
>>
>> Though, I admit I haven't looked at the MTK clocks *very deeply*, so I may be
>> misunderstanding something.
> 
> Not exactly. All the clocks in the MTK drivers are allocated at runtime,
> so we can't use clk_parent_data to point to not-yet-allocated clk_hw-s.
> Instead we'll need to have
> 
>      struct mtk_clk_parent_data {
>          unsigned int clk_id; /* Match CLK_XXX_YYY from dt-binding headers */
>          ... /* remaining fields same as mtk_clk_parent_data */
>      };
> 
> and create the actual clk_parent_data at runtime by looking up clk_id in
> the set of already registered clks:
> 
>      int mtk_clk_register_XXX(..., struct mtk_clk_parent_data *pdata,
>                               struct clk_hw_onecell_data *clk_data) {
>          struct clk_parent_data data = {
>              .hw = clk_data[pdata->clk_id],
>              /* copy other fields verbatim */
>          };
>          ...
>      }
> 
> Obviously this forces some ordering of how the clks are registered.
> I believe the order is already correct, and if it isn't, it would be
> easy to detect, and we can reorder things to fix it.
> 

That's clearer now, thanks for the overview!

>>> This would have to coexist with the existing helpers we have. So I think
>>> this work would be combined with the helper API cleanup / alignment with
>>> clk provider API.
>>>
>>> Does that make sense to you?
>>>
>>
>> Yes that does fully make sense to me.
>>
>>>> Of course, if you have concerns about old platforms that you cannot test,
>>>> or for which this kind of conversion would require a huge amount of effort,
>>>> then I would go for converting as many as possible as a first step and then
>>>> leave the others for later.
>>>>
>>>> I would envision MT8183, 8186, 8192, 8195 to be a good amount of first
>>>> candidates for this great effort.
>>>
>>> I'm working with MT8183 right now, as it can readily boot mainline to a
>>> shell. Depending on the schedule and whose on board with resources, I'd
> 
> * who's onboard *
> 

I can most probably promise you to spend some time in testing and reviewing.

Besides, when it comes to make things cleaner, proper, eventually as generic
as possible (read: upstream style), I'm always in. :-D

Also, I'm adding Nicolas Prado to the loop... as he may find this conversation
pretty interesting.

>>> probably handle the other ChromeOS platforms, or delegate it internally.
>>>
>>>
>>
>> That sounds like a plan. Besides, I wasn't trying to give you any hurry
>> whatsoever - I was simply thinking out loud :))
> 
> Got it. :)
> 
> 
> Regards
> ChenYu