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

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Message-ID: <CANk1AXSi0UrU+yHMz+B_gN-k9=DuTDHPaERQfwU+NHvWsaWDpQ@mail.gmail.com>
Date:	Thu, 10 Jul 2014 16:02:14 -0500
From:	Alan Tull <delicious.quinoa@...il.com>
To:	Rob Herring <robherring2@...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 1:52 PM, Rob Herring <robherring2@...il.com> wrote:
> 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?

No overlapping registers here.  Just various registers that are used
by: edac driver, fpga bridge, low power modes.  So no special
protection needed.

>
> Perhaps MFD is more appropriate than syscon?
>
> Rob

A syscon will do fine here.  If we did a MFD, all it would be doing
would be providing register access for this range of registers to a
few drivers, so syscon does that without any trouble.

Alan Tull
aka
delicious quinoa
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