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

Boris Brezillon
2016-10-18T19:45:25Z

On Tue, 18 Oct 2016 18:12:32 +0800
RogerCC.Lin <rogercc.lin@mediatek.com> wrote:

> On Tue, 2016-10-18 at 07:19 +0200, Boris Brezillon wrote:
> > 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?
> Tested, this patch is OK,
> Tested-by: RogerCC Lin <rogercc.lin@mediatek.com>

Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>

Brian, can you take this patch for the next -rc?

>
> >
> > > ---
> > > 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);
> >
>
>