[PATCH] spi: Mediatek: fix endian warnings
Russell King - ARM Linux
linux at arm.linux.org.uk
Sun Aug 16 07:06:39 PDT 2015
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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