[PATCH 02/28] [v2] mtd: mtk: avoid warning in mtk_ecc_encode

Arnd Bergmann
2016-10-17T22:07:37Z

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>
---
v2: move temporary buffer into struct mtk_ecc instead of having it
on the stack, as suggested by Boris Brezillon
---
drivers/mtd/nand/mtk_ecc.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/mtd/nand/mtk_ecc.c b/drivers/mtd/nand/mtk_ecc.c
index d54f666..dbf2562 100644
--- a/drivers/mtd/nand/mtk_ecc.c
+++ b/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);
--
2.9.0