linux-kernel - Re: [PATCH 1/3] dts: socfpga: Add bindings for Altera SoC SDRAM controller

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Date:	Tue, 8 Apr 2014 15:38:18 +0200
From:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
To:	tthayer@...era.com
Cc:	robherring2@...il.com, dougthompson@...ssion.com,
	grant.likely@...aro.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	rob@...dley.net, linux@....linux.org.uk, dinguyen@...era.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 1/3] dts: socfpga: Add bindings for Altera SoC SDRAM
 controller

Hi!

On Mon, Apr 07, 2014 at 04:54:07PM -0500, tthayer@...era.com wrote:
> From: Thor Thayer <tthayer@...era.com>
> 
> Addition of the Altera SDRAM controller bindings and device
> tree changes to the Altera SoC project.
> 
> Signed-off-by: Thor Thayer <tthayer@...era.com>
> To: Rob Herring <robherring2@...il.com>
> To: Pawel Moll <pawel.moll@....com>
> To: Mark Rutland <mark.rutland@....com>
> To: Ian Campbell <ijc+devicetree@...lion.org.uk>
> To: Kumar Gala <galak@...eaurora.org>
> To: Rob Landley <rob@...dley.net>
> To: Russell King <linux@....linux.org.uk>
> To: Dinh Nguyen <dinguyen@...era.com>
> Cc: devicetree@...r.kernel.org
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-arm-kernel@...ts.infradead.org
> ---
>  .../bindings/arm/altera/socfpga-sdram.txt          |   14 ++++++++++++++
>  arch/arm/boot/dts/socfpga.dtsi                     |    5 +++++
>  2 files changed, 19 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/altera/socfpga-sdram.txt
> 
> diff --git a/Documentation/devicetree/bindings/arm/altera/socfpga-sdram.txt b/Documentation/devicetree/bindings/arm/altera/socfpga-sdram.txt
> new file mode 100644
> index 0000000..525cb76
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/altera/socfpga-sdram.txt
> @@ -0,0 +1,14 @@
> +Altera SOCFPGA SDRAM Controller
> +
> +Required properties:
> +- compatible : "altr,sdr-ctl", "syscon";
> +                Note that syscon is invoked for this device to support the FPGA
> +		bridge driver, EDAC driver and other devices that share the
> +		registers.
> +- reg : Should contain 1 register ranges(address and length)

I haven't really thought this through, but why would the FPGA bridge driver
access the sdram controller? For releasing the resets in fpgaportrst ? Or is
there more?
Wouldn't it be more appropriate to represent those bits as a reset-controller to
some hypothetical IP core driver?
Then you could have something like

	hps2fpga@...00000 {
		ipcore@0 {
			resets = <&sdr 1>;
			reset-names = "foo";
			resets = <&rst 96>;
			reset-names = "bar";
			(...)
		};

		ipcore@...0 {
			resets = <&rst 96>;
			reset-names = "baz";
			(...)
		};
	};

And you would always have the correct bridges released out of reset for your
IP core. Does the FPGA bridge driver do more? I think that is basically it.
Where we maybe could run into problems though is the early_init stuff.

I think syscon is nice for some things, but we should try not to overuse it.

Regards,
Steffen

> +Example:
> +	sdrctl@...25000 {
> +		compatible = "altr,sdr-ctl", "syscon";
> +		reg = <0xffc25000 0x1000>;
> +	};
> diff --git a/arch/arm/boot/dts/socfpga.dtsi b/arch/arm/boot/dts/socfpga.dtsi
> index df43702..6ce912e 100644
> --- a/arch/arm/boot/dts/socfpga.dtsi
> +++ b/arch/arm/boot/dts/socfpga.dtsi
> @@ -676,6 +676,11 @@
>  			clocks = <&l4_sp_clk>;
>  		};
>  
> +		sdrctl@...25000 {
> +			compatible = "altr,sdr-ctl", "syscon";
> +			reg = <0xffc25000 0x1000>;
> +		};
> +
>  		rstmgr@...05000 {
>  			compatible = "altr,rst-mgr";
>  			reg = <0xffd05000 0x1000>;

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