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[PATCH] spi: Mediatek: fix endian warnings

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  [PATCH] spi: Mediatek: fix endian warnings Leilk Liu <leilk.liu@mediatek.com> - 2015-08-11 12:50 +0200
    Re: [PATCH] spi: Mediatek: fix endian warnings Jonas Gorski <jogo@openwrt.org> - 2015-08-12 16:50 +0200
      Re: [PATCH] spi: Mediatek: fix endian warnings lei liu <leilk.liu@mediatek.com> - 2015-08-13 04:20 +0200
        Re: [PATCH] spi: Mediatek: fix endian warnings Mark Brown <broonie@kernel.org> - 2015-08-13 11:30 +0200
    Re: [PATCH] spi: Mediatek: fix endian warnings Arnd Bergmann <arnd@arndb.de> - 2015-08-15 22:20 +0200
      Re: [PATCH] spi: Mediatek: fix endian warnings Arnd Bergmann <arnd@arndb.de> - 2015-08-15 22:20 +0200
      Re: [PATCH] spi: Mediatek: fix endian warnings Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-16 16:10 +0200
        Re: [PATCH] spi: Mediatek: fix endian warnings Mark Brown <broonie@kernel.org> - 2015-08-17 05:40 +0200

#1205040 — [PATCH] spi: Mediatek: fix endian warnings

This patch fixes endian warnings detected by sparse:
- sparse: incorrect type in argument 1 (different base types)
	  expected unsigned int [unsigned] val
	  got restricted __le32 [usertype] <noident>
- sparse: incorrect type in argument 1 (different base types)
	  expected unsigned int [unsigned] val
	  got restricted __le32 [usertype] <noident>

Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
---
 drivers/spi/spi-mt65xx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-mt65xx.c b/drivers/spi/spi-mt65xx.c
index 4676b01..ae645fa 100644
--- a/drivers/spi/spi-mt65xx.c
+++ b/drivers/spi/spi-mt65xx.c
@@ -359,9 +359,11 @@ static void mtk_spi_setup_dma_addr(struct spi_master *master,
 	struct mtk_spi *mdata = spi_master_get_devdata(master);
 
 	if (mdata->tx_sgl)
-		writel(cpu_to_le32(xfer->tx_dma), mdata->base + SPI_TX_SRC_REG);
+		writel((__force u32)cpu_to_le32(xfer->tx_dma),
+		       mdata->base + SPI_TX_SRC_REG);
 	if (mdata->rx_sgl)
-		writel(cpu_to_le32(xfer->rx_dma), mdata->base + SPI_RX_DST_REG);
+		writel((__force u32)cpu_to_le32(xfer->rx_dma),
+		       mdata->base + SPI_RX_DST_REG);
 }
 
 static int mtk_spi_fifo_transfer(struct spi_master *master,
-- 
1.8.1.1.dirty

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#1206173

Hi,

On Tue, Aug 11, 2015 at 12:43 PM, Leilk Liu <leilk.liu@mediatek.com> wrote:
> This patch fixes endian warnings detected by sparse:
> - sparse: incorrect type in argument 1 (different base types)
>           expected unsigned int [unsigned] val
>           got restricted __le32 [usertype] <noident>
> - sparse: incorrect type in argument 1 (different base types)
>           expected unsigned int [unsigned] val
>           got restricted __le32 [usertype] <noident>

This doesn't "fix" the warning, it only hides the warning and leaves
the actual issue unfixed.

>
> Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
> ---
>  drivers/spi/spi-mt65xx.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/spi/spi-mt65xx.c b/drivers/spi/spi-mt65xx.c
> index 4676b01..ae645fa 100644
> --- a/drivers/spi/spi-mt65xx.c
> +++ b/drivers/spi/spi-mt65xx.c
> @@ -359,9 +359,11 @@ static void mtk_spi_setup_dma_addr(struct spi_master *master,
>         struct mtk_spi *mdata = spi_master_get_devdata(master);
>
>         if (mdata->tx_sgl)
> -               writel(cpu_to_le32(xfer->tx_dma), mdata->base + SPI_TX_SRC_REG);
> +               writel((__force u32)cpu_to_le32(xfer->tx_dma),
> +                      mdata->base + SPI_TX_SRC_REG);
>         if (mdata->rx_sgl)
> -               writel(cpu_to_le32(xfer->rx_dma), mdata->base + SPI_RX_DST_REG);
> +               writel((__force u32)cpu_to_le32(xfer->rx_dma),
> +                      mdata->base + SPI_RX_DST_REG);

The issue here is that writel already does a cpu_to_le32 conversion,
so the extra cpu_to_le32 calls are actually bogus and need to be
removed. Else it will do a double conversion on big endian systems,
resulting in the data being written in big endian.


Jonas
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#1206465

Hello Mark,

 This patch is applied, should I append a new patch or you rollback it?
Thanks.

On Wed, 2015-08-12 at 16:45 +0200, Jonas Gorski wrote:
> Hi,
> 
> On Tue, Aug 11, 2015 at 12:43 PM, Leilk Liu <leilk.liu@mediatek.com> wrote:
> > This patch fixes endian warnings detected by sparse:
> > - sparse: incorrect type in argument 1 (different base types)
> >           expected unsigned int [unsigned] val
> >           got restricted __le32 [usertype] <noident>
> > - sparse: incorrect type in argument 1 (different base types)
> >           expected unsigned int [unsigned] val
> >           got restricted __le32 [usertype] <noident>
> 
> This doesn't "fix" the warning, it only hides the warning and leaves
> the actual issue unfixed.
> 
> >
> > Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
> > ---
> >  drivers/spi/spi-mt65xx.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/spi/spi-mt65xx.c b/drivers/spi/spi-mt65xx.c
> > index 4676b01..ae645fa 100644
> > --- a/drivers/spi/spi-mt65xx.c
> > +++ b/drivers/spi/spi-mt65xx.c
> > @@ -359,9 +359,11 @@ static void mtk_spi_setup_dma_addr(struct spi_master *master,
> >         struct mtk_spi *mdata = spi_master_get_devdata(master);
> >
> >         if (mdata->tx_sgl)
> > -               writel(cpu_to_le32(xfer->tx_dma), mdata->base + SPI_TX_SRC_REG);
> > +               writel((__force u32)cpu_to_le32(xfer->tx_dma),
> > +                      mdata->base + SPI_TX_SRC_REG);
> >         if (mdata->rx_sgl)
> > -               writel(cpu_to_le32(xfer->rx_dma), mdata->base + SPI_RX_DST_REG);
> > +               writel((__force u32)cpu_to_le32(xfer->rx_dma),
> > +                      mdata->base + SPI_RX_DST_REG);
> 
> The issue here is that writel already does a cpu_to_le32 conversion,
> so the extra cpu_to_le32 calls are actually bogus and need to be
> removed. Else it will do a double conversion on big endian systems,
> resulting in the data being written in big endian.
> 
> 
> Jonas


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#1206645

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On Thu, Aug 13, 2015 at 10:11:59AM +0800, lei liu wrote:

>  This patch is applied, should I append a new patch or you rollback it?
> Thanks.

Please send an incremental patch on top of what's applied and don't top
post.

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#1208153

On Tuesday 11 August 2015 18:43:09 Leilk Liu wrote:
> @@ -359,9 +359,11 @@ static void mtk_spi_setup_dma_addr(struct spi_master *master,
>         struct mtk_spi *mdata = spi_master_get_devdata(master);
>  
>         if (mdata->tx_sgl)
> -               writel(cpu_to_le32(xfer->tx_dma), mdata->base + SPI_TX_SRC_REG);
> +               writel((__force u32)cpu_to_le32(xfer->tx_dma),
> +                      mdata->base + SPI_TX_SRC_REG);
>         if (mdata->rx_sgl)
> -               writel(cpu_to_le32(xfer->rx_dma), mdata->base + SPI_RX_DST_REG);
> +               writel((__force u32)cpu_to_le32(xfer->rx_dma),
> +                      mdata->base + SPI_RX_DST_REG);
>  }
> 

This looks wrong: writel takes a CPU-endian argument, so the value returned
from cpu_to_le32() is not appropriate.

The warning is correct, and you have to remove the cpu_to_le32() conversion
in order to get the driver to behave correctly when the kernel is built
as big-endian.

	Arnd
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#1208154

On Saturday 15 August 2015 22:16:03 Arnd Bergmann wrote:
> On Tuesday 11 August 2015 18:43:09 Leilk Liu wrote:
> > @@ -359,9 +359,11 @@ static void mtk_spi_setup_dma_addr(struct spi_master *master,
> >         struct mtk_spi *mdata = spi_master_get_devdata(master);
> >  
> >         if (mdata->tx_sgl)
> > -               writel(cpu_to_le32(xfer->tx_dma), mdata->base + SPI_TX_SRC_REG);
> > +               writel((__force u32)cpu_to_le32(xfer->tx_dma),
> > +                      mdata->base + SPI_TX_SRC_REG);
> >         if (mdata->rx_sgl)
> > -               writel(cpu_to_le32(xfer->rx_dma), mdata->base + SPI_RX_DST_REG);
> > +               writel((__force u32)cpu_to_le32(xfer->rx_dma),
> > +                      mdata->base + SPI_RX_DST_REG);
> >  }
> > 
> 
> This looks wrong: writel takes a CPU-endian argument, so the value returned
> from cpu_to_le32() is not appropriate.
> 
> The warning is correct, and you have to remove the cpu_to_le32() conversion
> in order to get the driver to behave correctly when the kernel is built
> as big-endian.

Nevermind, I now saw the issue has already been raised.

	Arnd
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#1208240

On Sat, Aug 15, 2015 at 10:16:03PM +0200, Arnd Bergmann wrote:
> On Tuesday 11 August 2015 18:43:09 Leilk Liu wrote:
> > @@ -359,9 +359,11 @@ static void mtk_spi_setup_dma_addr(struct spi_master *master,
> >         struct mtk_spi *mdata = spi_master_get_devdata(master);
> >  
> >         if (mdata->tx_sgl)
> > -               writel(cpu_to_le32(xfer->tx_dma), mdata->base + SPI_TX_SRC_REG);
> > +               writel((__force u32)cpu_to_le32(xfer->tx_dma),
> > +                      mdata->base + SPI_TX_SRC_REG);
> >         if (mdata->rx_sgl)
> > -               writel(cpu_to_le32(xfer->rx_dma), mdata->base + SPI_RX_DST_REG);
> > +               writel((__force u32)cpu_to_le32(xfer->rx_dma),
> > +                      mdata->base + SPI_RX_DST_REG);
> >  }
> > 
> 
> This looks wrong: writel takes a CPU-endian argument, so the value returned
> from cpu_to_le32() is not appropriate.
> 
> The warning is correct, and you have to remove the cpu_to_le32() conversion
> in order to get the driver to behave correctly when the kernel is built
> as big-endian.

Indeed, it's about time people started thinking more about the warnings
and why we have coded things in the way we have.

Look people.  cpu_to_le32() takes a value in the CPU endian, and
converts it to a little endian 32-bit number.  See, the clue is in
the name.

All writel() implementations take a CPU number and write it in little
endian format.  Hence, writel() almost always uses cpu_to_le32()
internally.

Now think about what you're saying with "cpu_to_le32(cpu_to_le32())".
It's utter rubbish, total crap.  It's wrong no matter which way you
look at it.

We have le32_to_cpu() which does what it says on the tin.  Same with
be32_to_cpu() and cpu_to_be32().

Don't hack around this stuff with __force.  If you're having to use
__force to get rid of a warning here, you _ARE_ doing something wrong,
no questions about that.  __force in driver code is a definite sign
that you are doing something wrong.  Don't do it.  Ask the question
if you think you need it.

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#1208342

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On Sun, Aug 16, 2015 at 03:06:39PM +0100, Russell King - ARM Linux wrote:

> All writel() implementations take a CPU number and write it in little
> endian format.  Hence, writel() almost always uses cpu_to_le32()
> internally.

I think the reason this keeps coming up is that people aren't expecting
writel() to be doing endianness conversion, it's easy to get caught out
by it.

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