linux-kernel - Re: [PATCH 5/5] clk: mediatek: Add MediaTek Helio X10 MT6795 clock drivers

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Date:   Tue, 17 May 2022 10:48:04 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, robh+dt@...nel.org
Cc:     krzysztof.kozlowski+dt@...aro.org, mturquette@...libre.com,
        sboyd@...nel.org, p.zabel@...gutronix.de, y.oudjana@...tonmail.com,
        jason-jh.lin@...iatek.com, ck.hu@...iatek.com,
        fparent@...libre.com, rex-bc.chen@...iatek.com,
        tinghan.shen@...iatek.com, chun-jie.chen@...iatek.com,
        weiyi.lu@...iatek.com, ikjn@...omium.org, miles.chen@...iatek.com,
        sam.shih@...iatek.com, wenst@...omium.org,
        bgolaszewski@...libre.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-clk@...r.kernel.org,
        konrad.dybcio@...ainline.org, marijn.suijten@...ainline.org,
        martin.botka@...ainline.org, ~postmarketos/upstreaming@...ts.sr.ht,
        phone-devel@...r.kernel.org, paul.bouchara@...ainline.org,
        kernel@...labora.com
Subject: Re: [PATCH 5/5] clk: mediatek: Add MediaTek Helio X10 MT6795 clock
 drivers

Hi Angelo,

On 17/05/2022 10:07, AngeloGioacchino Del Regno wrote:
> Il 16/05/22 13:30, Matthias Brugger ha scritto:
>>
>>
>> On 13/05/2022 18:50, AngeloGioacchino Del Regno wrote:
>>> Add the clock drivers for the entire clock tree of MediaTek Helio X10
>>> MT6795, including system clocks (apmixedsys, infracfg, pericfg, topckgen)
>>> and multimedia clocks (mmsys, mfg, vdecsys, vencsys).
>>>
>>> Signed-off-by: AngeloGioacchino Del Regno 
>>> <angelogioacchino.delregno@...labora.com>
>>
>> Thanks a lot for taking care of this!
>> I just wonder if we couldn't build most of the clock drivers as modules like 
>> done for the mt6779. It would help us to keep the kernel image smaller.
>>
> 
> Hello Matthias!
> 
> You're welcome!
> ...but I simply couldn't stand at seeing partially working (..or actually, not
> really working) SoCs upstream. If something is upstream, it must work, or it
> shouldn't be here for real :-)
> 
> Regarding your question about the clock drivers as module... I believe we can,
> but that'd be only for {vdec,venc}sys and *maybe* MFG (gpu clocks): I don't know
> if it'd be worth to do, as these are about... 8 clocks out of... I haven't counted
> them, but more than 250, I think?
> 
> It *should* be straightforward though, just about giving them a tristate in Kconfig
> instead of a bool, but that would still be limited to just those three...
> 

I think you could guide yourself by looking at
f09b9460a5e4 ("clk: mediatek: support COMMON_CLK_MT6779 module build")


I think having clocks as modules is a criteria to be part of Android's Generic 
Kernel Image. Not that we target this here, just for your information (in case 
you didn't know).

> The reason for me excluding clk-mt6795-mm from this choice is that - at least for
> me - my development platform is a commercial smartphone, where the only thing that
> "saves you" is having some display output... I mean - I *do* have a UART port, but
> that's only because I've been able to solder thin wires on 0.2mm pads... you surely
> agree on the fact that this isn't a common practice, even across developers.
> 

Yes I was wondering if you got some development smartphone or you did the 
soldering. I have some solder knowledge but I think not enough to solder 
something like this :D

> Besides, if you think that clk-mt6795-mm should indeed be a module by default,
> well, that.. is.. possible - I don't see why it shouldn't be... obviously keeping
> in mind that this will largely slow down the boot process, which isn't a big issue.
> 

Well I don't want to bother you with minor details, most important thing is that 
we get support upstream... but ;) you can always mark the modules as compiled 
in, even if it's tristate, which in your case you want to do.

> In any case, it is *not* possible to compile as module *any* of the clock drivers
> that I have included in the CONFIG_COMMON_CLK_MT6795 (apmixed, infra, peri, topck)
> as.. you know.. these are "a bit critical" on older platforms :-)
> 
> 
> How would you proceed?
> 

I'd make all the drivers that theoretically can be build as modules tristate, 
you can then define for your development environment to make them build-in.

Sounds good?

Regards,
Matthias