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

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Date:	Tue, 8 Apr 2014 09:29:50 -0500
From:	Thor Thayer <tthayer@...era.com>
To:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
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

On Tue, 2014-04-08 at 15:38 +0200, Steffen Trumtrar wrote:
> 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.
> > 
[snip]
> > +
> > +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?

Hi Steffan. No, not for resets. We need to enable the FPGA to SDRAM
path. Our SDRAM controller allows FPGA master access to the SDRAM.

> 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.

Understood. In this case, syscon seems to be appropriate.
> 
> 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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