Re: [PATCH v7 2/2] memory: atmel-ebi: add DT bindings documentation

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi Rob,

On Tue, 3 May 2016 11:40:19 -0500
Rob Herring <robh@kernel.org> wrote:

> On Thu, Apr 28, 2016 at 02:03:27PM +0200, Boris Brezillon wrote:
> > The EBI (External Bus Interface) is used to access external peripherals
> > (NOR, SRAM, NAND, and other specific devices like ethernet controllers).
> > Each device is assigned a CS line and an address range and can have its
> > own configuration (timings, access mode, bus width, ...).
> > This driver provides a generic DT binding to configure a device according
> > to its requirements.
> > For specific device controllers (like the NAND one) the SMC timings
> > should be configured by the controller driver through the matrix and smc
> > syscon regmaps.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > ---
> >  .../bindings/memory-controllers/atmel,ebi.txt      | 136 +++++++++++++++++++++
> >  1 file changed, 136 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..a6dca5c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/memory-controllers/atmel,ebi.txt
> > @@ -0,0 +1,136 @@
> > +* 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 through the SMC
> > +(Static Memory Controller).
> > +
> > +Required properties:
> > +
> > +- compatible:		"atmel,at91sam9260-ebi"
> > +			"atmel,at91sam9261-ebi"
> > +			"atmel,at91sam9263-ebi0"
> > +			"atmel,at91sam9263-ebi1"  
> 
> What are the differences between 0 and 1?

Because this SoC has 2 EBI busses with different capabilities.

> 
> > +			"atmel,at91sam9rl-ebi"
> > +			"atmel,at91sam9g45-ebi"
> > +			"atmel,at91sam9x5-ebi"
> > +			"atmel,sama5d3-ebi"
> > +
> > +- reg:			Contains offset/length value for EBI memory mapping.
> > +			This property might contain several entries if the EBI
> > +			memory range is not contiguous
> > +
> > +- #address-cells:	Must be 2.
> > +			The first cell encodes the CS.
> > +			The second cell encode the offset into the CS memory
> > +			range.
> > +
> > +- #size-cells:		Must be set to 1.
> > +
> > +- ranges:		Encodes CS to memory region association.
> > +
> > +- clocks:		Clock feeding the EBI controller.
> > +			See clock-bindings.txt
> > +
> > +Children device nodes are representing device connected to the EBI bus.
> > +
> > +Required device node properties:
> > +
> > +- #reg:			Contains the chip-select id, the offset and the length  
> 
> s/#reg/reg/

Will fix that.

> 
> > +			of the memory region requested by the device.
> > +
> > +EBI bus configuration associated with specific chip-select will be defined in
> > +the configs subnode. This configs node will in turn contain several subnodes
> > +named config-<cs-id>, each of them containing the following properties.  
> 
> This is a bit unusual. Why not just part of the child device nodes?

Oh, come on! I reworked the binding because Mark complained about the
previous binding which was doing exactly what you're suggesting. Can
you please be consistent in your reviews... 


> 
> > +
> > +Optional config-<cs-id> node properties:
> > +
> > +- atmel,bus-width:		width of the asynchronous device's data bus
> > +				8, 16 or 32.
> > +				Default to 8 when undefined.
> > +
> > +- atmel,byte-access-type	"write" or "select" (see Atmel datasheet).
> > +				Default to "select" when undefined.
> > +
> > +- atmel,read-mode		"nrd" or "ncs".
> > +				Default to "ncs" when undefined.
> > +
> > +- atmel,write-mode		"nwe" or "ncs".
> > +				Default to "ncs" when undefined.
> > +
> > +- atmel,exnw-mode		"disabled", "frozen" or "ready".
> > +				Default to "disabled" when undefined.
> > +
> > +- atmel,page-mode		enable page mode if present. The provided value
> > +				defines the page size (supported values: 4, 8,
> > +				16 and 32).
> > +
> > +- atmel,tdf-mode:		"normal" or "optimized". When set to  
> 
> This should be boolean.

It was a formerly defined as a boolean, and when it's done like that we
have no way to identify whether the property was forgotten or
intentionally set to normal mode. What's the problem with this approach?

> 
> > +				"optimized" the data float time is optimized
> > +				depending on the next device being accessed
> > +				(next device setup time is subtracted to the
> > +				current device data float time).
> > +				Default to "normal" when undefined.
> > +
> > +Mandatory timings expressed in nanoseconds (see Atmel datasheet for a full
> > +description).  
> 
> Required first, then optional properties please.

Okay.

> 
> > +
> > +- atmel,ncs-rd-setup-ns
> > +- atmel,nrd-setup-ns
> > +- atmel,ncs-wr-setup-ns
> > +- atmel,nwe-setup-ns
> > +- atmel,ncs-rd-pulse-ns
> > +- atmel,nrd-pulse-ns
> > +- atmel,ncs-wr-pulse-ns
> > +- atmel,nwe-pulse-ns
> > +- atmel,nwe-cycle-ns
> > +- atmel,nrd-cycle-ns
> > +- atmel,tdf-ns
> > +
> > +Example:
> > +
> > +	ebi: ebi@10000000 {
> > +		compatible = "atmel,sama5d3-ebi";
> > +		#address-cells = <2>;
> > +		#size-cells = <1>;  
> 
> > +		atmel,smc = <&hsmc>;
> > +		atmel,matrix = <&matrix>;  
> 
> What are these? 
> 
> > +		reg = <0x10000000 0x10000000
> > +		       0x40000000 0x30000000>;
> > +		ranges = <0x0 0x0 0x10000000 0x10000000
> > +			  0x1 0x0 0x40000000 0x10000000
> > +			  0x2 0x0 0x50000000 0x10000000
> > +			  0x3 0x0 0x60000000 0x10000000>;
> > +		clocks = <&mck>;
> > +
> > +		pinctrl-names = "default";
> > +		pinctrl-0 = <&pinctrl_ebi_addr>;  
> 
> Not documented.

Will document those properties.

Regards,

Boris


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