mtd: nand: Create helpers to set/extract the ECC requirements

Despite its current name, the eccreq field actually encodes both the
NAND requirements and the final ECC configuration. That works fine when
using on-die ECC since those 2 concepts match perfectly, but it starts
being a problem as soon as we use on-host ECC engines, where we're not
guaranteed to have a perfect match.

Let's hide the ECC requirements access behind helpers so we can later
split those 2 concepts. As the structures have not been clarified yet,
these helpers access the same internal variable as
nanddev_get_ecc_conf() for now.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200827085208.16276-14-miquel.raynal@bootlin.com

include/linux/mtd/nand.h

@@ -533,6 +533,30 @@ nanddev_get_ecc_conf(struct nand_device *nand)
 	return &nand->eccreq;
 }
 
+/**
+ * nanddev_get_ecc_requirements() - Extract the ECC requirements from a NAND
+ *                                  device
+ * @nand: NAND device
+ */
+static inline const struct nand_ecc_props *
+nanddev_get_ecc_requirements(struct nand_device *nand)
+{
+	return &nand->eccreq;
+}
+
+/**
+ * nanddev_set_ecc_requirements() - Assign the ECC requirements of a NAND
+ *                                  device
+ * @nand: NAND device
+ * @reqs: Requirements
+ */
+static inline void
+nanddev_set_ecc_requirements(struct nand_device *nand,
+			     const struct nand_ecc_props *reqs)
+{
+	nand->eccreq = *reqs;
+}
+
 int nanddev_init(struct nand_device *nand, const struct nand_ops *ops,
 		 struct module *owner);
 void nanddev_cleanup(struct nand_device *nand);