14.06.2019 18:24, Jon Hunter пишет: > > 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/20190424162348.23692-1-ben.dooks@xxxxxxxxxxxxxxx/ >>> >>> Inspired-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> >>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> >>> --- >>> 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. Looks like everything should be fine as-is. BTW, it's a bit hard to believe that there is any real benefit from the free_dma_desc list at all, maybe worth to just remove it?
