On Mon, Oct 09, 2017 at 10:43:54AM +0100, Jon Hunter wrote:
>
>
> On 06/10/17 20:11, Dmitry Osipenko wrote:
> > On 04.10.2017 02:58, Dmitry Osipenko wrote:
> >> AHB DMA controller presents on Tegra20/30 SoC's, it supports transfers
> >> memory <-> AHB bus peripherals as well as mem-to-mem transfers. Driver
> >> doesn't yet implement transfers larger than 64K and scatter-gather
> >> transfers that have NENT > 1, HW doesn't have native support for these
> >> cases, mem-to-mem isn't implemented as well.
> >>
> >> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> >> ---
> >> drivers/dma/Kconfig | 10 +
> >> drivers/dma/Makefile | 1 +
> >> drivers/dma/tegra20-ahb-dma.c | 630 ++++++++++++++++++++++++++++++++++++++++++
> >> 3 files changed, 641 insertions(+)
> >> create mode 100644 drivers/dma/tegra20-ahb-dma.c
>
>
> ...
>
> >> +static struct tegra_ahbdma_tx_desc *tegra_ahbdma_get_next_tx(
> >> + struct tegra_ahbdma_chan *chan)
> >> +{
> >> + struct virt_dma_desc *vdesc = vchan_next_desc(&chan->vchan);
> >> +
> >> + if (vdesc)
> >> + list_del(&vdesc->node);
> >
> > I just noticed that this is incorrect. Node must be deleted after TX completion,
> > otherwise vchan_find_desc won't find TX and residual won't be reported by
> > dmaengine_tx_status.
> >
> > Jon, I think you ADMA driver has the same issue, as well as several other DMA
> > drivers that use virt-dma.
>
> Actually, I think that the above is correct. If vchan_find_desc() finds
> the descriptor then this indicates that the transfer has not started yet
> and so the residual is equal to the transfer size.
That is correct, so you can do a quick calculation and find the residue only
for current one
> If you look at the adma driver, you will see the if vchan_find_desc()
> does not find the descriptor, then we check to see if the current
> transfer is the one we are querying and if so return the bytes
> remaining. Looking at this driver again, what you have in
> tegra_ahbdma_tx_status() does not look correct. You should have
> something like ...
>
> vdesc = vchan_find_desc(&ahbdma_chan->vchan, cookie);
> if (vdesc) {
> tx = to_ahbdma_tx_desc(vdesc);
> residual = tx->csr & AHBDMA_CH_WCOUNT_MASK;
> } else if (ahbdma_chan->tx_active &&
> ahbdma_chan->tx_active->vd.tx.cookie == cookie) {
> residual = tegra_ahbdma_residual(ahbdma_chan);
> } else {
> residual = 0;
> }
>
> Cheers
> Jon
>
> --
> nvpublic
--
~Vinod
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