On 13/06/2019 22:08, Dmitry Osipenko wrote: > Tegra's APB DMA engine updates words counter after each transferred burst > of data, hence it can report transfer's residual with more fidelity which > may be required in cases like audio playback. In particular this fixes > audio stuttering during playback in a chromiuim web browser. The patch is > based on the original work that was made by Ben Dooks [1]. It was tested > on Tegra20 and Tegra30 devices. > > [1] > https://lore.kernel.org/lkml/[email protected]/ > > Inspired-by: Ben Dooks <[email protected]> > Signed-off-by: Dmitry Osipenko <[email protected]> > --- > drivers/dma/tegra20-apb-dma.c | 35 ++++++++++++++++++++++++++++------- > 1 file changed, 28 insertions(+), 7 deletions(-) > > diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c > index 79e9593815f1..c5af8f703548 100644 > --- a/drivers/dma/tegra20-apb-dma.c > +++ b/drivers/dma/tegra20-apb-dma.c > @@ -797,12 +797,36 @@ static int tegra_dma_terminate_all(struct dma_chan *dc) > return 0; > } > > +static unsigned int tegra_dma_update_residual(struct tegra_dma_channel *tdc, > + struct tegra_dma_sg_req *sg_req, > + struct tegra_dma_desc *dma_desc, > + unsigned int residual) > +{ > + unsigned long status, wcount = 0; > + > + if (!list_is_first(&sg_req->node, &tdc->pending_sg_req)) > + return residual; > + > + if (tdc->tdma->chip_data->support_separate_wcount_reg) > + wcount = tdc_read(tdc, TEGRA_APBDMA_CHAN_WORD_TRANSFER); > + > + status = tdc_read(tdc, TEGRA_APBDMA_CHAN_STATUS); > + > + if (!tdc->tdma->chip_data->support_separate_wcount_reg) > + wcount = status; > + > + if (status & TEGRA_APBDMA_STATUS_ISE_EOC) > + return residual - sg_req->req_len; > + > + return residual - get_current_xferred_count(tdc, sg_req, wcount); > +} > + > static enum dma_status tegra_dma_tx_status(struct dma_chan *dc, > dma_cookie_t cookie, struct dma_tx_state *txstate) > { > struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc); > + struct tegra_dma_sg_req *sg_req = NULL; > struct tegra_dma_desc *dma_desc; > - struct tegra_dma_sg_req *sg_req; > enum dma_status ret; > unsigned long flags; > unsigned int residual; > @@ -838,6 +862,8 @@ static enum dma_status tegra_dma_tx_status(struct > dma_chan *dc, > residual = dma_desc->bytes_requested - > (dma_desc->bytes_transferred % > dma_desc->bytes_requested); > + residual = tegra_dma_update_residual(tdc, sg_req, dma_desc, > + residual);
I had a quick look at this, I am not sure that we want to call tegra_dma_update_residual() here for cases where the dma_desc is on the free_dma_desc list. In fact, couldn't this be simplified a bit for case where the dma_desc is on the free list? In that case I believe that the residual should always be 0. Cheers Jon -- nvpublic
