2015-08-13 12:07:07

by Leilk Liu

Subject: [PATCH] spi: Mediatek: fixup cpu_to_le32 incorrect usage

writel() already does a cpu_to_le32 conversion, so
remove cpu_to_le32().

Signed-off-by: Leilk Liu <[email protected]>
---
drivers/spi/spi-mt65xx.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-mt65xx.c b/drivers/spi/spi-mt65xx.c
index ae645fa..519f50c 100644
--- a/drivers/spi/spi-mt65xx.c
+++ b/drivers/spi/spi-mt65xx.c
@@ -359,11 +359,9 @@ 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((__force u32)cpu_to_le32(xfer->tx_dma),
- mdata->base + SPI_TX_SRC_REG);
+ writel(xfer->tx_dma, mdata->base + SPI_TX_SRC_REG);
if (mdata->rx_sgl)
- writel((__force u32)cpu_to_le32(xfer->rx_dma),
- mdata->base + SPI_RX_DST_REG);
+ writel(xfer->rx_dma, mdata->base + SPI_RX_DST_REG);
}

static int mtk_spi_fifo_transfer(struct spi_master *master,
--
1.8.1.1.dirty

2015-08-15 20:46:40

by Arnd Bergmann

Subject: Re: [PATCH] spi: Mediatek: fixup cpu_to_le32 incorrect usage

On Thursday 13 August 2015 20:06:41 Leilk Liu wrote:
> diff --git a/drivers/spi/spi-mt65xx.c b/drivers/spi/spi-mt65xx.c
> index ae645fa..519f50c 100644
> --- a/drivers/spi/spi-mt65xx.c
> +++ b/drivers/spi/spi-mt65xx.c
> @@ -359,11 +359,9 @@ 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((__force u32)cpu_to_le32(xfer->tx_dma),
> - mdata->base + SPI_TX_SRC_REG);
> + writel(xfer->tx_dma, mdata->base + SPI_TX_SRC_REG);
> if (mdata->rx_sgl)
> - writel((__force u32)cpu_to_le32(xfer->rx_dma),
> - mdata->base + SPI_RX_DST_REG);
> + writel(xfer->rx_dma, mdata->base + SPI_RX_DST_REG);
> }
>
> static int mtk_spi_fifo_transfer(struct spi_master *master,
> --
>

This change looks good, but after I've briefly looked at the current driver,
I found at least one more location that looks like an endianess bug:


+static int mtk_spi_fifo_transfer(struct spi_master *master,
+ struct spi_device *spi,
+ struct spi_transfer *xfer)
+{
...
+
+ for (i = 0; i < cnt; i++)
+ writel(*((u32 *)xfer->tx_buf + i),
+ mdata->base + SPI_TX_DATA_REG);
+
+ mtk_spi_enable_transfer(master);
+
+ return 1;
+}

Here, you write data into a FIFO register using an accessor that converts
to little-endian. In contrast, the DMA based accessor apparently has
no byte swap, so most likely one of the two is broken on big-endian
systems. My guess is that the look above is wrong, and you need to
use iowrite32_rep() instead, so you always write into the FIFO in
the byte stream order (first byte to last byte) rather than swapping
32-bit entities.

The other suspicious part is this:

+ reg_val |= (chip_config->tx_endian << SPI_CMD_TX_ENDIAN_OFFSET);
+ reg_val |= (chip_config->rx_endian << SPI_CMD_RX_ENDIAN_OFFSET);

It's not clear what the tx_endian/rx_endian bits refer to and why you
can't just always set the register interface to little-endian. If it's
set to big-endian, you probably need to add more byte swaps in the
driver.

Arnd