On Wednesday 16 May 2007, Haavard Skinnemoen wrote:
> When either rx_buf or tx_buf is not being used, i.e. for plain read-
> or write operations, the atmel_spi uses a fixed-size DMA buffer
> instead. If the transfer is longer than the size of this buffer, it is
> split into multiple DMA transfers.
>
> When the transfer is split like this, the atmel_spi driver ends up
> using the same DMA address again and again even for the buffer that
> came from the user, which is of course wrong.
Yes, and needs fixing. This is almost right, see below.
> Fix this by adding the
> number of bytes already transferred to the DMA address so that the
> data ends up in the right place.
>
> Thanks to Wu Xuan for discovering this bug.
>
> Signed-off-by: Haavard Skinnemoen <[email protected]>
> ---
> drivers/spi/atmel_spi.c | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
> index 1d8a2f6..8b2601d 100644
> --- a/drivers/spi/atmel_spi.c
> +++ b/drivers/spi/atmel_spi.c
> @@ -113,16 +113,16 @@ static void atmel_spi_next_xfer(struct spi_master *master,
>
> len = as->remaining_bytes;
>
> - tx_dma = xfer->tx_dma;
> - rx_dma = xfer->rx_dma;
> + tx_dma = xfer->tx_dma + xfer->len - len;
> + rx_dma = xfer->rx_dma + xfer->len - len;
>
> /* use scratch buffer only when rx or tx data is unspecified */
> - if (rx_dma == INVALID_DMA_ADDRESS) {
> + if (!xfer->rx_buf) {
This test ...
> rx_dma = as->buffer_dma;
> if (len > BUFFER_SIZE)
> len = BUFFER_SIZE;
> }
> - if (tx_dma == INVALID_DMA_ADDRESS) {
> + if (!xfer->tx_buf) {
... and this one must not assume that the relevant buffer
is always NULL when the tx_dma has been set up. Keep the
test against INVALID_DMA_ADDRESS, but fetch the address
from the spi_transfer.
It's legit to set up cpu-virtual (for PIO) and dma addresses
for each buffer, since the upper layer driver has no way to
know if the underlying controller driver is DMA-capable, or
for that matter PIO-capable.
> tx_dma = as->buffer_dma;
> if (len > BUFFER_SIZE)
> len = BUFFER_SIZE;
> --
> 1.4.4.4
>
-
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