[v3 1/2] dma: mmp_pdma: add support for residue reporting

[Xiang Wang]

On 08/15/2013 12:19 AM, Daniel Mack wrote:
> In order to report the channel's residue, we have to memorize the first
> dma buffer position when the channel is configured.
>
> Signed-off-by: Daniel Mack <zonque at gmail.com>
> ---
>   drivers/dma/mmp_pdma.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 43 insertions(+), 2 deletions(-)
>

> +static unsigned int mmp_pdma_residue(struct mmp_pdma_chan *chan)
> +{
> +	struct mmp_pdma_desc_sw *sw;
> +	u32 curr, done = 0;
> +
> +	if (chan->dir == DMA_DEV_TO_MEM)
> +		curr = readl(chan->phy->base + DTADR(chan->phy->idx));
One concern for this patch:
If we call dmaengine_tx_status() after dma_do_tasklet at mmp_pdma.c, 
chan->phy will most likely to be NULL.
dma_do_tasklet() -> start_pending_queue() -> mmp_pdma_free_phy()

For why do we call dmaengine_tx_status() after a DMA interrupt:
briefly, if we use DMA to handle device trailing bytes, it'll report a 
DMA interrupt. We need to get to know how many bytes have been received 
in the IRQ handler.
We've discussed about this in the link below:
http://thread.gmane.org/gmane.linux.kernel/1500713

-- 
Regards,
Xiang