linux-kernel - Re: [PATCH v2 06/11] memory: atmel-ebi: add DT bindings documentation

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Message-ID: <20141105173957.1726d369@bbrezillon>
Date:	Wed, 5 Nov 2014 17:39:57 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Jean-Jacques Hiblot <jjhiblot@...phandler.com>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Andrew Victor <linux@...im.org.za>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	devicetree <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/11] memory: atmel-ebi: add DT bindings
 documentation

On Wed, 5 Nov 2014 17:22:57 +0100
Jean-Jacques Hiblot <jjhiblot@...phandler.com> wrote:

> Hi Boris,
> 
> 2014-11-05 17:01 GMT+01:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
> > Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> > ---
> >  .../bindings/memory-controllers/atmel-ebi.txt      | 153 +++++++++++++++++++++
> >  1 file changed, 153 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/memory-controllers/atmel-ebi.txt
> >
> > diff --git a/Documentation/devicetree/bindings/memory-controllers/atmel-ebi.txt b/Documentation/devicetree/bindings/memory-controllers/atmel-ebi.txt
> > new file mode 100644
> > index 0000000..dc2c34f
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/memory-controllers/atmel-ebi.txt
> > @@ -0,0 +1,153 @@
> > +* Device tree bindings for Atmel EBI
> > +
> > +The External Bus Interface (EBI) controller is a bus where you can connect
> > +asynchronous (NAND, NOR, SRAM, ....) and synchronous memories (SDR/DDR SDRAMs).
> > +The EBI provides a glue-less interface to asynchronous memories though the SMC
> > +(Static Memory Controller).
> > +Synchronous memories (and some asynchronous memories like NANDs) can be
> > +attached to specialized controllers which are responsible for configuring the
> > +bus appropriately according to the connected device.
> > +In the other hand, the bus interface can be automated for simple asynchronous
> > +devices.

[...]

> > +
> > +Optional child cs node properties:
> > +- atmel,generic-dev            boolean property specifying if the device is
> > +                               a generic device.
> > +                               The following properties are only parsed if
> > +                               this property is present.
> > +                               Specialized devices are attached to specialized
> > +                               controllers which should configure the bus
> > +                               appropriately.
> 
> What do you mean by specialized devices ? Can you give an example ?

The ones I have in mind are NAND chips: the NAND controller can
automatically discover the required timings and configure the SMC
accordingly. In that case there's no need to specify timings in the DT,
because they will/should be dynalically configured by the NAND
controller driver.

But more generally, the datasheet describe 2 modes for some CS ports:
1) the generic mode, which bind the device to the generic SMC engine
2) the specialized mode which binds it to a specific HW block

This mode can be configured in CCFG_EBICSA, and the specialized mode
supported by each CS depends on each SoC.
For example, for the at91sam9x5:
CS1 => DDR2SDR controller
CS3 => NAND Flash Controller/Logic

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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