linux-kernel - Re: [PATCH 0/3] Apple M1 clock gate driver

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Date:   Fri, 4 Jun 2021 10:43:48 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Sven Peter <sven@...npeter.dev>
Cc:     Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hector Martin <marcan@...can.st>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH 0/3] Apple M1 clock gate driver

Hi,

* Sven Peter <sven@...npeter.dev> [210603 12:56]:
> Another possibility this made me think of is to instead just use the clocks
> property the way it's usually used and simply refer to the controller itself, e.g.
> 
> #define APPLE_CLK_UART0  0x270
> #define APPLE_CLK_UART_P 0x220
> #define APPLE_CLK_SIO    0x1c0
> 
> pmgr0: clock-controller@...700000 {
>         compatible = "apple,t8103-gate-clock";
>         #clock-cells = <1>;
>         reg = <0x2 0x3b700000 0x0 0x4000>;
>         clock-indices = <APPLE_CLK_SIO>, <APPLE_CLK_UART_P>, <APPLE_CLK_UART0>;
>         clock-output-names = "clock-sio", "clock-uart-", "clock-uart0";
>         clocks = <&some_dummy_root_clock>, <&pmgr0 APPLE_CLK_SIO>,
>                  <&pmgr0 APPLE_CLK_UART_P>;
> };

How about the following where you set up the gate clocks as separate child nodes:

pmgr0: clock-controller@...700000 {
	compatible = "apple,foo-clock-controller";
	#clock-cells = <1>;
	reg = <0x2 0x3b700000 0x0 0x4000>;

	clk_uart0: clock@270 {
		compatible = "apple,t8103-gate-clock";
		#clock-cells = <0>;
		assigned-clock-parents = <&pmgr0 APPLE_CLK_SIO>,
					 <&pmgr0 APPLE_CLK_UART_P>;
		// ...
	};

};

Keep the clock controller still addressable by offset from base as discussed,
and additionally have the driver parse and set up the child node clocks.

Then I think the consumer driver can just do:

serial0: serial@...200000 {
	// ...
	clocks = <&clk_uart0>, <&clk24>;
	clock-names = "uart", "clk_uart_baud0";
	// ...
};

Regards,

Tony