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

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Date:	Tue, 8 Apr 2014 13:52:31 -0500
From:	Rob Herring <robherring2@...il.com>
To:	delicious quinoa <delicious.quinoa@...il.com>
Cc:	Steffen Trumtrar <s.trumtrar@...gutronix.de>,
	Thor Thayer <tthayer@...era.com>,
	Doug Thompson <dougthompson@...ssion.com>,
	Grant Likely <grant.likely@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Dinh Nguyen <dinguyen@...era.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 1/3] dts: socfpga: Add bindings for Altera SoC SDRAM controller

On Tue, Apr 8, 2014 at 11:02 AM, delicious quinoa
<delicious.quinoa@...il.com> wrote:
> On Tue, Apr 8, 2014 at 9:33 AM, Steffen Trumtrar
> <s.trumtrar@...gutronix.de> wrote:
>> On Tue, Apr 08, 2014 at 09:29:50AM -0500, Thor Thayer wrote:
>>> 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.
>>>
>>
>> Yes. But what you have to do to enable the path is let the FPGA port you use
>> out of reset. And that is it as far as I can see. The rest happens in the
>> bitstream. Or is there more to enable the path?
>> The FPGA2SDRAM bridge is the one I didn't use as of yet, so if I miss something
>> please elaborate.
>
> Hi Steffen,
>
> The sdram controller is used by two drivers.  That's why we want to
> specify "syscon" here.  The other driver is the FPGA bridge driver.
> Its functionality is very separate from what this driver is doing (we
> are not enabling the bridge in this driver; we are enabling the
> monitoring and resetting the interrupt bit of the EDAC).  We wanted to
> specify "syscon" her so that we don't have to have to change it for
> the other driver.

But are there actually overlapping registers which are accessed by
both drivers and need the protection of regmap?

Perhaps MFD is more appropriate than syscon?

Rob
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