linux-kernel - Re: [PATCH v8 0/6] arm/arm64: mediatek: Fix mmsys device probing

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Message-ID: <6355f1fd-b929-730e-e0f6-96dd5100e3f9@collabora.com>
Date:   Wed, 26 Feb 2020 10:24:04 +0100
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     CK Hu <ck.hu@...iatek.com>
Cc:     mark.rutland@....com, Kate Stewart <kstewart@...uxfoundation.org>,
        Minghsiu Tsai <minghsiu.tsai@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>, airlied@...ux.ie,
        mturquette@...libre.com, dri-devel@...ts.freedesktop.org,
        Richard Fontana <rfontana@...hat.com>,
        laurent.pinchart@...asonboard.com, ulrich.hecht+renesas@...il.com,
        Collabora Kernel ML <kernel@...labora.com>,
        linux-clk@...r.kernel.org, Nicolas Boichat <drinkcat@...omium.org>,
        Weiyi Lu <weiyi.lu@...iatek.com>,
        Krzysztof Kozlowski <krzk@...nel.org>, wens@...e.org,
        Allison Randal <allison@...utok.net>,
        mtk01761 <wendell.lin@...iatek.com>,
        Owen Chen <owen.chen@...iatek.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        p.zabel@...gutronix.de, frank-w@...lic-files.de,
        Seiya Wang <seiya.wang@...iatek.com>, sean.wang@...iatek.com,
        Houlong Wei <houlong.wei@...iatek.com>, robh+dt@...nel.org,
        linux-mediatek@...ts.infradead.org, hsinyi@...omium.org,
        Matthias Brugger <"matthias. bgg"@gmail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Matthias Brugger <mbrugger@...e.com>,
        Fabien Parent <fparent@...libre.com>, sboyd@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rdunlap@...radead.org, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel@...ll.ch>, matthias.bgg@...nel.org
Subject: Re: [PATCH v8 0/6] arm/arm64: mediatek: Fix mmsys device probing

Hi CK,

On 26/2/20 6:32, CK Hu wrote:

[snip]

>>
>> How do you see move mmsys to drivers/soc/mediatek and instantiate the clk and
>> mediatek-drm driver
>>
>>  mmsys: syscon@...00000 {
>>  	compatible = "mediatek,mt8173-mmsys", "syscon", "simple-mfd";
>>  	reg = <0 0x14000000 0 0x1000>;
>>  	power-domains = <&scpsys MT8173_POWER_DOMAIN_MM>;
>>
>> 	clock-controller {
>> 		compatible = "mediatek,clk-mt8173-mm"
>> 		assigned-clocks = <&topckgen CLK_TOP_MM_SEL>;
>> 	 	assigned-clock-rates = <400000000>;
>>  		#clock-cells = <1>;
>> 	};
>>
>> 	display-subsystem {
>> 		compatible = "mediatek,display-subsystem";
>> 	};
>>  };
>>
> 
> Let's start with the simple definition.
> 
> mmsys: syscon at 14000000 {
> 	compatible = "mediatek,mt8173-mmsys", "syscon";
> 	reg = <0 0x14000000 0 0x1000>;
> 	power-domains = <&scpsys MT8173_POWER_DOMAIN_MM>;
> 	assigned-clocks = <&topckgen CLK_TOP_MM_SEL>;
> 	assigned-clock-rates = <400000000>;
> 	#clock-cells = <1>;
> };
> 
> When we break clock control to a sub device of mmsys, the reason is that
> 'Linux' generally categorize clock controller to a device. When we break
> display control to a sub device of mmsys, the reason is that 'Linux'
> generally categorize display controller to a device. All these seems
> software-oriented reason, so I think we do not break any sub device and
> keep mmsys simple.
> 
> When I search of_clk_add_provider(), I find that not all clock provider
> code is in drivers/clk. Maybe when a clock controller is not an
> independent device, the driver code of clock controller could be placed
> within the device driver it belonged to. We could place mmsys driver in
> drivers/soc/mediatek/, and it control the clock, routing, fake engine,
> memory delay,.... I would like drm driver to be placed in
> drivers/gpu/drm/ because display function block, such as OVL, does not
> belong to mmsys device. And finally let mmsys driver to probe
> mediatek-drm driver.
> 

You can apply the same reasoning in the clk subsystem, not all the drivers in
drivers/clk are pure clock controllers, some of them are already
system-controller or "simple-mfd" and some of them even instantiate other
subdrivers via the platform register API.

Note that moving clk-<chip>-mm drivers to drivers/soc/mediatek will imply move a
lot of code, I'll focus only on mt8173 for now because is the only platform I
can really test. Let me prepare a v9 and lets see how looks like.

Thanks,
 Enric

> Regards,
> CK

[snip]