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

[RogerCC.Lin <rogercc.lin@mediatek.com>]

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>

> 
> > ---
> > 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);
>