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

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  [PATCH 02/28] [v2] mtd: mtk: avoid warning in mtk_ecc_encode Arnd Bergmann <arnd@arndb.de> - 2016-10-18 00:10 +0200
    Re: [PATCH 02/28] [v2] mtd: mtk: avoid warning in mtk_ecc_encode Boris Brezillon <boris.brezillon@free-electrons.com> - 2016-10-18 07:30 +0200
      Re: [PATCH 02/28] [v2] mtd: mtk: avoid warning in mtk_ecc_encode Boris Brezillon <boris.brezillon@free-electrons.com> - 2016-10-18 21:50 +0200

#1502512 — [PATCH 02/28] [v2] 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>
---
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

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#1502699

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);

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#1503312

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);  
> >   
> 
> 

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