Re: [PATCH] dma : EG20T PCH: Fix miss-setting DMA descriptor

[Dan Williams]

2010/12/1 Tomoya MORINAGA <tomoya-linux@xxxxxxxxxxxxxxx>:
> From: Tomoya MORINAGA <tomoya-linux@xxxxxxxxxxxxxxx>
>
>
>
> Currently, in case of using scatter/gather mode, head of data is not sent to
>
> destination. The cause is second descriptor address is set to NEXT.
>
> The NEXT must have head of descriptor address.
>
> This patch sets head of descriptor address to the NEXT.
>
>
>
> Signed-off-by: Tomoya MORINAGA <tomoya-linux@xxxxxxxxxxxxxxx>
> ---
>  drivers/dma/pch_dma.c |   15 ++++++++-------
>  1 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/dma/pch_dma.c b/drivers/dma/pch_dma.c
> index 92b6790..a3d54c0 100644
> --- a/drivers/dma/pch_dma.c
> +++ b/drivers/dma/pch_dma.c
[..]
> @@ -273,10 +268,16 @@ static void pdc_dostart(struct pch_dma_chan *pd_chan, struct pch_dma_desc* desc)
>        dev_dbg(chan2dev(&pd_chan->chan), "chan %d -> next: %x\n",
>                pd_chan->chan.chan_id, desc->regs.next);
>
> -       if (list_empty(&desc->tx_list))
> +       if (list_empty(&desc->tx_list)) {
> +               channel_writel(pd_chan, DEV_ADDR, desc->regs.dev_addr);
> +               channel_writel(pd_chan, MEM_ADDR, desc->regs.mem_addr);
> +               channel_writel(pd_chan, SIZE, desc->regs.size);
> +               channel_writel(pd_chan, NEXT, desc->regs.next);
>                pdc_set_mode(&pd_chan->chan, DMA_CTL0_ONESHOT);
> -       else
> +       } else {
> +               channel_writel(pd_chan, NEXT, virt_to_phys(&desc->regs));

There is a reason for the following comment for virt_to_phys():

/*      This function does not give bus mappings for DMA transfers. In
 *      almost all conceivable cases a device driver should not be using
 *      this function
 */

...in this case this wants to be:

     channel_write(pd_chan, NEXT, desc->txd.phys);

I'll let Yong comment on the correctness of the rest.

--
Dan
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/