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

Boris Brezillon
2016-10-18T05:19:59Z

On Tue, 18 Oct 2016 00:05:31 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> 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>

Jorge, RogerCC, can I have an Acked-by and/or Tested-by for this patch?

> ---
> 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);