On 18/06/2019 12:50, 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. It was tested on > Tegra20 and Tegra30 devices. > > Link: https://lore.kernel.org/lkml/20190424162348.23692-1-ben.dooks@xxxxxxxxxxxxxxx/ > Inspired-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> > Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> > --- > > Changelog: > > v2: Addressed review comments made by Jon Hunter to v1. We won't try > to get words count if dma_desc is on free list as it will result > in a NULL dereference because this case wasn't handled properly. > > The residual value is now updated properly, avoiding potential > integer overflow by adding the "bytes" to the "bytes_transferred" > instead of the subtraction. > > drivers/dma/tegra20-apb-dma.c | 33 ++++++++++++++++++++++++++------- > 1 file changed, 26 insertions(+), 7 deletions(-) > > diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c > index 79e9593815f1..fed18bc46479 100644 > --- a/drivers/dma/tegra20-apb-dma.c > +++ b/drivers/dma/tegra20-apb-dma.c > @@ -797,6 +797,28 @@ static int tegra_dma_terminate_all(struct dma_chan *dc) > return 0; > } > > +static unsigned int tegra_dma_sg_bytes_xferred(struct tegra_dma_channel *tdc, > + struct tegra_dma_sg_req *sg_req) > +{ > + unsigned long status, wcount = 0; > + > + if (!list_is_first(&sg_req->node, &tdc->pending_sg_req)) > + return 0; > + > + 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 sg_req->req_len; > + > + return 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) > { > @@ -806,6 +828,7 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc, > enum dma_status ret; > unsigned long flags; > unsigned int residual; > + unsigned int bytes = 0; > > ret = dma_cookie_status(dc, cookie, txstate); > if (ret == DMA_COMPLETE) > @@ -825,6 +848,7 @@ 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) { > + bytes = tegra_dma_sg_bytes_xferred(tdc, sg_req); > ret = dma_desc->dma_status; > goto found; > } > @@ -836,7 +860,7 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc, > found: > if (dma_desc && txstate) { > residual = dma_desc->bytes_requested - > - (dma_desc->bytes_transferred % > + ((dma_desc->bytes_transferred + bytes) % > dma_desc->bytes_requested); > dma_set_residue(txstate, residual); > } > @@ -1441,12 +1465,7 @@ static int tegra_dma_probe(struct platform_device *pdev) > BIT(DMA_SLAVE_BUSWIDTH_4_BYTES) | > BIT(DMA_SLAVE_BUSWIDTH_8_BYTES); > tdma->dma_dev.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV); > - /* > - * XXX The hardware appears to support > - * DMA_RESIDUE_GRANULARITY_BURST-level reporting, but it's > - * only used by this driver during tegra_dma_terminate_all() > - */ > - tdma->dma_dev.residue_granularity = DMA_RESIDUE_GRANULARITY_SEGMENT; > + tdma->dma_dev.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST; > tdma->dma_dev.device_config = tegra_dma_slave_config; > tdma->dma_dev.device_terminate_all = tegra_dma_terminate_all; > tdma->dma_dev.device_tx_status = tegra_dma_tx_status; > Looks good to me. Thanks for fixing! Reviewed-by: Jon Hunter <jonathanh@xxxxxxxxxx> Cheers Jon -- nvpublic
