On Fri, May 31, 2013 at 11:21 AM, Xiang Wang <wangx...@gmail.com> wrote:
> In some of our drivers (e.g. UART) we may stop a running DMA
> before it finishes. So we need to know how many bytes have
> been transferred.
Couple of comments below.
> --- a/drivers/dma/mmp_pdma.c
> +++ b/drivers/dma/mmp_pdma.c
> @@ -589,7 +638,13 @@ static int mmp_pdma_control(struct dma_chan *dchan, enum
> dma_ctrl_cmd cmd,
> mmp_pdma_free_desc_list(chan, &chan->chain_pending);
> mmp_pdma_free_desc_list(chan, &chan->chain_running);
> spin_unlock_irqrestore(&chan->desc_lock, flags);
> - chan->idle = true;
> + chan->status = DMA_SUCCESS;
> + chan->bytes_residue = 0;
> + break;
> + case DMA_PAUSE:
> + disable_chan(chan->phy);
> + chan->status = DMA_PAUSED;
> + chan->bytes_residue = mmp_pdma_get_bytes_residue(chan);
Does it mean user has to do DMA_PAUSE first to get more or less
accurate residue?
Logically that sound correct, but in general we may allow user to get
approximate residue value of on going transfer.
> break;
> case DMA_SLAVE_CONFIG:
> if (cfg->direction == DMA_DEV_TO_MEM) {
> @@ -637,7 +692,8 @@ static enum dma_status mmp_pdma_tx_status(struct dma_chan
> *dchan,
> unsigned long flags;
>
> spin_lock_irqsave(&chan->desc_lock, flags);
> - ret = dma_cookie_status(dchan, cookie, txstate);
> + ret = chan->status;
> + dma_set_residue(txstate, chan->bytes_residue);
> spin_unlock_irqrestore(&chan->desc_lock, flags);
Besides my patch which removes this spinlock I think the workflow
should be something like
status = dma_cookie_status()
if status == DMA_SUCCESS or !txstate:
return status
dma_set_residue()
return status
Because there is no reason to return residue of successfully finished
transfer. It should be 0.
--
With Best Regards,
Andy Shevchenko
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