dt-bindings: mtd: Document Macronix NAND device bindings

Document the bindings used by the Macronix NAND device.

Signed-off-by: Mason Yang <masonccyang@mxic.com.tw>
Reviewed-by: Rob Herring <robh@kernel.org>
[<miquel.raynal@bootlin.com: Fix typos]
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1581922600-25461-3-git-send-email-masonccyang@mxic.com.tw

diff --git a/Documentation/devicetree/bindings/mtd/nand-macronix.txt b/Documentation/devicetree/bindings/mtd/nand-macronix.txt
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+Macronix NANDs Device Tree Bindings
+-----------------------------------
+
+Macronix NANDs support randomizer operation for scrambling user data,
+which can be enabled with a SET_FEATURE. The penalty when using the
+randomizer are subpage accesses prohibited and more time period needed
+for program operation, i.e., tPROG 300us to 340us (randomizer enabled).
+Enabling the randomizer is a one time persistent and non reversible
+operation.
+
+For more high-reliability concern, if subpage write is not available
+with hardware ECC and not enabled at UBI level, then enabling the
+randomizer is recommended by default by adding a new specific property
+in children nodes.
+
+Required NAND chip properties in children mode:
+- randomizer enable: should be "mxic,enable-randomizer-otp"
+
+Example:
+
+       nand: nand-controller@unit-address {
+
+               nand@0 {
+                       reg = <0>;
+                       mxic,enable-randomizer-otp;
+               };
+       };