Re: [PATCH 7/8] dmaengine: tegra20-apb-dma: Only calculate residue if txstate exists.

Vinod Koul
2016-06-21T16:01:39Z

On Wed, Jun 08, 2016 at 09:51:57AM +0100, Jon Hunter wrote:
> Hi Peter,
>
> On 07/06/16 18:38, Peter Griffin wrote:
> > There is no point calculating the residue if there is
> > no txstate to store the value.
> >
> > Signed-off-by: Peter Griffin <peter.griffin-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> > ---
> > drivers/dma/tegra20-apb-dma.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> > index 01e316f..7f4af8c 100644
> > --- a/drivers/dma/tegra20-apb-dma.c
> > +++ b/drivers/dma/tegra20-apb-dma.c
> > @@ -814,7 +814,7 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
> > unsigned int residual;
> >
> > ret = dma_cookie_status(dc, cookie, txstate);
> > - if (ret == DMA_COMPLETE)
> > + if (ret == DMA_COMPLETE || !txstate)
> > return ret;
>
> Thanks for reporting this. I agree that we should not do this, however,
> looking at the code for Tegra, I am wondering if this could change the
> actual state that is returned. Looking at dma_cookie_status() it will
> call dma_async_is_complete() which will return either DMA_COMPLETE or
> DMA_IN_PROGRESS. It could be possible that the actual state for the
> DMA transfer in the tegra driver is DMA_ERROR, so I am wondering if we
> should do something like the following ...

This one is stopping code execution when residue is not valid. Do notice
that it check for DMA_COMPLETE OR txstate. In other cases, wit will return
'that' state when txstate is NULL.

I am going to apply this.

>
> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> index 01e316f73559..45edab7418d0 100644
> --- a/drivers/dma/tegra20-apb-dma.c
> +++ b/drivers/dma/tegra20-apb-dma.c
> @@ -822,13 +822,8 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
> /* Check on wait_ack desc status */
> list_for_each_entry(dma_desc, &tdc->free_dma_desc, node) {
> if (dma_desc->txd.cookie == cookie) {
> - residual = dma_desc->bytes_requested -
> - (dma_desc->bytes_transferred %
> - dma_desc->bytes_requested);
> - dma_set_residue(txstate, residual);
> ret = dma_desc->dma_status;
> - spin_unlock_irqrestore(&tdc->lock, flags);
> - return ret;
> + goto found;
> }
> }
>
> @@ -836,17 +831,23 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
> list_for_each_entry(sg_req, &tdc->pending_sg_req, node) {
> dma_desc = sg_req->dma_desc;
> if (dma_desc->txd.cookie == cookie) {
> - residual = dma_desc->bytes_requested -
> - (dma_desc->bytes_transferred %
> - dma_desc->bytes_requested);
> - dma_set_residue(txstate, residual);
> ret = dma_desc->dma_status;
> - spin_unlock_irqrestore(&tdc->lock, flags);
> - return ret;
> + goto found;
> }
> }
>
> - dev_dbg(tdc2dev(tdc), "cookie %d does not found\n", cookie);
> + dev_warn(tdc2dev(tdc), "cookie %d not found\n", cookie);
> + spin_unlock_irqrestore(&tdc->lock, flags);
> + return ret;
> +
> +found:
> + if (txstate) {
> + residual = dma_desc->bytes_requested -
> + (dma_desc->bytes_transferred %
> + dma_desc->bytes_requested);
> + dma_set_residue(txstate, residual);
> + }
> +

I feel this optimizes stuff, which seems okay. Feel free to send as proper
patch.

> spin_unlock_irqrestore(&tdc->lock, flags);
> return ret;
> }
>
> Cheers
> Jon
>
> --
> nvpublic

--
~Vinod