On 14/06/2019 16:21, Jon Hunter wrote: > > 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.
Actually, no, it could be non-zero in the case the transfer is aborted. Jon -- nvpublic
