mtd: fsl-quadspi: Distinguish the mtd device names

Currently on a imx6sx-sdb board, which has two SPI NOR chips connected
to QSPI2 the following output from /proc/mtd is seen:

dev:    size   erasesize  name
mtd0: 01000000 00010000 "21e4000.qspi"
mtd1: 01000000 00010000 "21e4000.qspi"

Attempts to partition them on the kernel command line result in both
chips with identical (and identically named) partitions, which is
an inconvenient behavior.

Assign a different mtd->name for each mtd device to avoid this problem.

After this change the output from /proc/mtd becomes:

dev:    size   erasesize  name
mtd0: 01000000 00010000 "21e4000.qspi-0"
mtd1: 01000000 00010000 "21e4000.qspi-1"

In order to keep mtdparts compatibility keep the mtd->name
unchanged when a single SPI NOR is present.

Reported-by: David Wolfe <david.wolfe@nxp.com>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Han Xu <han.xu@nxp.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/spi-nor/fsl-quadspi.c

@@ -1051,6 +1051,24 @@ static int fsl_qspi_probe(struct platform_device *pdev)
 		spi_nor_set_flash_node(nor, np);
 		nor->priv = q;
 
+		if (q->nor_num > 1 && !mtd->name) {
+			int spiflash_idx;
+
+			ret = of_property_read_u32(np, "reg", &spiflash_idx);
+			if (!ret) {
+				mtd->name = devm_kasprintf(dev, GFP_KERNEL,
+							   "%s-%d",
+							   dev_name(dev),
+							   spiflash_idx);
+				if (!mtd->name) {
+					ret = -ENOMEM;
+					goto mutex_failed;
+				}
+			} else {
+				dev_warn(dev, "reg property is missing\n");
+			}
+		}
+
 		/* fill the hooks */
 		nor->read_reg = fsl_qspi_read_reg;
 		nor->write_reg = fsl_qspi_write_reg;