mtd: mtk: avoid warning in mtk_ecc_encode

When building with -Wmaybe-uninitialized, gcc produces a silly false positive
warning for the mtk_ecc_encode function:

drivers/mtd/nand/mtk_ecc.c: In function 'mtk_ecc_encode':
drivers/mtd/nand/mtk_ecc.c:402:15: error: 'val' may be used uninitialized in this function [-Werror=maybe-uninitialized]

The function for some reason contains a double byte swap on big-endian
builds to get the OOB data into the correct order again, and is written
in a slightly confusing way.

Using a simple memcpy32_fromio() to read the data simplifies it a lot
so it becomes more readable and produces no warning. However, the
output might not have 32-bit alignment, so we have to use another
memcpy to avoid taking alignment faults or writing beyond the end
of the array.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: RogerCC Lin <rogercc.lin@mediatek.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

Author: arndb

drivers/mtd/nand/mtk_ecc.c

@@ -86,6 +86,8 @@ struct mtk_ecc {
 	struct completion done;
 	struct mutex lock;
 	u32 sectors;
+
+	u8 eccdata[112];
 };
 
 static inline void mtk_ecc_wait_idle(struct mtk_ecc *ecc,
@@ -366,9 +368,8 @@ int mtk_ecc_encode(struct mtk_ecc *ecc, struct mtk_ecc_config *config,
 		   u8 *data, u32 bytes)
 {
 	dma_addr_t addr;
-	u8 *p;
-	u32 len, i, val;
-	int ret = 0;
+	u32 len;
+	int ret;
 
 	addr = dma_map_single(ecc->dev, data, bytes, DMA_TO_DEVICE);
 	ret = dma_mapping_error(ecc->dev, addr);
@@ -393,14 +394,12 @@ int mtk_ecc_encode(struct mtk_ecc *ecc, struct mtk_ecc_config *config,
 
 	/* Program ECC bytes to OOB: per sector oob = FDM + ECC + SPARE */
 	len = (config->strength * ECC_PARITY_BITS + 7) >> 3;
-	p = data + bytes;
 
-	/* write the parity bytes generated by the ECC back to the OOB region */
-	for (i = 0; i < len; i++) {
-		if ((i % 4) == 0)
-			val = readl(ecc->regs + ECC_ENCPAR(i / 4));
-		p[i] = (val >> ((i % 4) * 8)) & 0xff;
-	}
+	/* write the parity bytes generated by the ECC back to temp buffer */
+	__ioread32_copy(ecc->eccdata, ecc->regs + ECC_ENCPAR(0), round_up(len, 4));
+
+	/* copy into possibly unaligned OOB region with actual length */
+	memcpy(data + bytes, ecc->eccdata, len);
 timeout:
 
 	dma_unmap_single(ecc->dev, addr, bytes, DMA_TO_DEVICE);