linux-kernel - Re: [PATCH 0/5] Add Mediatek MT8173 subsystem clocks support

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Date:	Mon, 8 Jun 2015 15:27:51 +0800
From:	James Liao <jamesjj.liao@...iatek.com>
To:	Stephen Boyd <sboyd@...eaurora.org>,
	Sascha Hauer <kernel@...gutronix.de>
CC:	Sascha Hauer <s.hauer@...gutronix.de>,
	Mike Turquette <mturquette@...aro.org>,
	<srv_heupstream@...iatek.com>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Henry Chen <henryc.chen@...iatek.com>,
	Ricky Liang <jcliang@...omium.org>,
	Rob Herring <robh+dt@...nel.org>,
	<linux-mediatek@...ts.infradead.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	"Eddie Huang" <eddie.huang@...iatek.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/5] Add Mediatek MT8173 subsystem clocks support

Hi Stephen,

On Fri, 2015-06-05 at 17:59 -0700, Stephen Boyd wrote:
> Perhaps an example would be best. In DT we would have:
> 
> 	vencsys: vencsys@...00 {
> 		compatible = "mtk,vencsys";
> 		reg = <0x10000 0x1000>;
> 		#clock-cells = <1>;
> 		#reset-cells = <1>;
> 	};
> 
> 	myconsumer@...00 {
> 		compatible = "mtk,vencsys";
> 		reg = <0x12000 0x100>;
> 		clocks = <&vencsys 10>;
> 		clock-names = "core";
> 	};
> 
> 	(Or are the consumers only children of the subsystem?
> 	It's not clear to me)

In our case the vencsys clocks may use used by its own driver and other
drivers (such as SMI driver).

> And then in the mtk,vencsys driver we would create a platform
> device named something like "mtk-vencsys-clk" and assign the
> of_node of the device to be the of_node that is assigned to the
> mtk,vencsys device.
> 
> 	static int vencsys_probe(struct platform_device *pdev)
> 	{
> 		int ret;
> 		struct device_node *np = pdev->dev.of_node;
> 		struct platform_device *clk_pdev;
> 
> 		clk_pdev = platform_device_alloc("mtk-vencsys-clk", -1);
> 		clk_pdev->dev.of_node = of_node;
> 		ret = platform_device_add(clk_pdev);
> 		if (ret)
> 			return ret;
> 	}
> 
> Then we could put a mtk-vencsys-clk driver in drivers/clk/ that
> does the clk driver part...
> 
> 	static int clk_vencsys_probe(struct platform_device *pdev)
> 	{
> 		int ret;
> 		struct device_node *np = pdev->dev.of_node;
> 		struct regmap *regmap;
> 
> 		ret = of_clk_add_provider(np, of_clk_src_onecell_get, ..);
> 		if (ret)
> 			return ret;
> 
> 		regmap = dev_get_regmap(pdev->dev.parent, NULL);
> 
> 	}
> 
> And similar things could be done for the reset driver.
> 

It looks like there is only one DT node (vencsys@...00) but there are
several drivers refer to this DT node, and then we use a dummy driver
(or a "top driver") to aggregate drivers with different features (clk,
reset etc.).

It means we need to provide vencsys clk driver in drivers/clk and
vencsys reset driver in drivers/reset, and also to provide a vencsys top
driver in, for example, soc/mediatek, right?

Now we have 3 choice:

1. implement vencsys clock driver and reset driver in drivers/clk.
2. implement vencsys clock driver and reset driver in drivers/soc.
3. implement vencsys clock driver in drivers/clk, vencsys reset driver
in drivers/reset, and vencsys top driver in drivers/soc.

Sascha, do you have comments for these 3 solutions?


Best regards,

James

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