mtd: rawnand: arasan: Prevent an unsupported configuration

Under the following conditions:
* after rounding up by 4 the number of bytes to transfer (this is
  related to the controller's internal constraints),
* if this (rounded) amount of data is situated beyond the end of the
  device,
* and only in NV-DDR mode,
the Arasan NAND controller timeouts.

This currently can happen in a particular helper used when picking
software ECC algorithms. Let's prevent this situation by refusing to use
the NV-DDR interface with software engines.

Fixes: 4edde60314 ("mtd: rawnand: arasan: Support NV-DDR interface")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211008163640.1753821-1-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/arasan-nand-controller.c

@@ -973,6 +973,21 @@ static int anfc_setup_interface(struct nand_chip *chip, int target,
 		nvddr = nand_get_nvddr_timings(conf);
 		if (IS_ERR(nvddr))
 			return PTR_ERR(nvddr);
+
+		/*
+		 * The controller only supports data payload requests which are
+		 * a multiple of 4. In practice, most data accesses are 4-byte
+		 * aligned and this is not an issue. However, rounding up will
+		 * simply be refused by the controller if we reached the end of
+		 * the device *and* we are using the NV-DDR interface(!). In
+		 * this situation, unaligned data requests ending at the device
+		 * boundary will confuse the controller and cannot be performed.
+		 *
+		 * This is something that happens in nand_read_subpage() when
+		 * selecting software ECC support and must be avoided.
+		 */
+		if (chip->ecc.engine_type == NAND_ECC_ENGINE_TYPE_SOFT)
+			return -ENOTSUPP;
 	} else {
 		sdr = nand_get_sdr_timings(conf);
 		if (IS_ERR(sdr))