Re: [RFC PATCH 1/2] dt-bindings: mtd: Add Cavium SOCs NAND bindings

On Tue, Mar 28, 2017 at 10:20:35PM +0200, Boris Brezillon wrote:

Hi Jan,

On Mon, 27 Mar 2017 18:05:23 +0200
Jan Glauber [off-list ref] wrote:

quoted

Add device tree binding description for Cavium SOC nand flash controller.

CC: Rob Herring <redacted>
CC: Mark Rutland <redacted>
CC: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

Signed-off-by: Jan Glauber <jglauber-YGCgFSpz5w/QT0dZR+AlfA@public.gmane.org>
---
 .../devicetree/bindings/mtd/cavium_nand.txt        | 32 ++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/cavium_nand.txt

diff --git a/Documentation/devicetree/bindings/mtd/cavium_nand.txt b/Documentation/devicetree/bindings/mtd/cavium_nand.txt
new file mode 100644
index 0000000..4698d1f
--- /dev/null
+++ b/Documentation/devicetree/bindings/mtd/cavium_nand.txt

@@ -0,0 +1,32 @@
+* Cavium NAND controller
+
+Required properties:
+
+- compatible:		should be "cavium,cn8xxx-nand"
+- reg:			PCI devfn
+- clocks:		must contain system clock
+- #address-cells:	<1>
+- #size-cells:		<0>
+
+The nand flash controller may contain up to 8 subnodes representing
+NAND flash chips. Their properties are as follows.
+
+Required properties:
+- compatible:		should be "cavium,nandcs"

Why do you need a compatible here? All sub-nodes should be representing
NAND devices connected to the NAND controller. If you need an extra
subnode to represent something that is not a NAND device, then it should
not have a reg property, so testing if reg is present to detect if the
subnode is reprensenting a NAND device should be enough.

Am I missing something?

Hi Boris,

You're right. We don't need or check this compatible. The chip type
which would make more sense than what I used above is detected via ONFI,
so I can just remove the compatible string.

quoted

+- reg:			a single integer representing the chip-select number
+- nand-ecc-mode:	see nand.txt
+
+Example:
+
+nfc: nand@b,0 {

        ^ nand-controller@xxx

OK.

quoted

+	compatible = "cavium,cn8xxx-nand";
+	reg = <0x5800 0 0 0 0>;
+	clocks = <&sclk>;
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	nand@1 {
+		compatible = "cavium,nandcs";
+		reg = <1>;
+		nand-ecc-mode = "on-die";
+};

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