Re: [PATCH v10 3/5] mtd: nand: vf610_nfc: add device tree bindings

[Brian Norris <computersforpeace-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Sorry, I realized a potential issue here.

On Mon, Aug 03, 2015 at 11:27:28AM +0200, Stefan Agner wrote:
> Signed-off-by: Bill Pringlemeir <bpringlemeir-ygJ1pmMJ17cAvxtiuMwx3w@public.gmane.org>
> Acked-by: Shawn Guo <shawnguo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Reviewed-by: Brian Norris <computersforpeace-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Signed-off-by: Stefan Agner <stefan-XLVq0VzYD2Y@public.gmane.org>
> ---
>  .../devicetree/bindings/mtd/vf610-nfc.txt          | 45 ++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mtd/vf610-nfc.txt
> 
> diff --git a/Documentation/devicetree/bindings/mtd/vf610-nfc.txt b/Documentation/devicetree/bindings/mtd/vf610-nfc.txt
> new file mode 100644
> index 0000000..cae5f25
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mtd/vf610-nfc.txt
> @@ -0,0 +1,45 @@
> +Freescale's NAND flash controller (NFC)
> +
> +This variant of the Freescale NAND flash controller (NFC) can be found on
> +Vybrid (vf610), MPC5125, MCF54418 and Kinetis K70.
> +
> +Required properties:
> +- compatible: Should be set to "fsl,vf610-nfc"
> +- reg: address range of the NFC
> +- interrupts: interrupt of the NFC
> +- nand-bus-width: see nand.txt
> +- nand-ecc-mode: see nand.txt
> +- nand-on-flash-bbt: see nand.txt

Stumbling across the "multi-CS" questions on the driver reminds me: it
typically makes sense to define new NAND bindings using separate NAND
*controller* and *flash* device nodes. The above 3 properties, at least,
would apply on a per-flash basis, not per-controller typically. See
sunxi-nand, for instance:

http://lxr.free-electrons.com/source/Documentation/devicetree/bindings/mtd/sunxi-nand.txt

brcmnand had a similar pattern:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/mtd/brcm,brcmnand.txt

(Perhaps it's time we standardized this a little more formally...)

> +- assigned-clocks: main clock from the SoC, for Vybrid <&clks VF610_CLK_NFC>;
> +- assigned-clock-rates: The NAND bus timing is derived from this clock
> +    rate and should not exceed maximum timing for any NAND memory chip
> +    in a board stuffing. Typical NAND memory timings derived from this
> +    clock are found in the SoC hardware reference manual. Furthermore,
> +    there might be restrictions on maximum rates when using hardware ECC.
> +
> +- #address-cells, #size-cells : Must be present if the device has sub-nodes
> +  representing partitions.
> +
> +Required properties for hardware ECC:
> +- nand-ecc-strength: supported strengths are 24 and 32 bit (see nand.txt)
> +- nand-ecc-step-size: step size equals page size, currently only 2k pages are
> +    supported
> +
> +Example:
> +
> +	nfc: nand@400e0000 {
> +		compatible = "fsl,vf610-nfc";
> +		#address-cells = <1>;
> +		#size-cells = <1>;
> +		reg = <0x400e0000 0x4000>;
> +		interrupts = <GIC_SPI 83 IRQ_TYPE_LEVEL_HIGH>;
> +		clocks = <&clks VF610_CLK_NFC>;
> +		clock-names = "nfc";
> +		assigned-clocks = <&clks VF610_CLK_NFC>;
> +		assigned-clock-rates = <33000000>;
> +		nand-bus-width = <8>;
> +		nand-ecc-mode = "hw";
> +		nand-ecc-strength = <32>;
> +		nand-ecc-step-size = <2048>;
> +		nand-on-flash-bbt;
> +	};

Brian
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