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

Rob Herring
2014-04-08T18:52:37Z

On Tue, Apr 8, 2014 at 11:02 AM, delicious quinoa
<delicious.quinoa@gmail.com> wrote:
> On Tue, Apr 8, 2014 at 9:33 AM, Steffen Trumtrar
> <s.trumtrar@pengutronix.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@altera.com wrote:
>>> > > From: Thor Thayer <tthayer@altera.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