21.06.2019 0:58, Dmitry Osipenko пишет: > 20.06.2019 11:38, Jon Hunter пишет: >> >> 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/[email protected]/ >>> Inspired-by: Ben Dooks <[email protected]> >>> Signed-off-by: Dmitry Osipenko <[email protected]> >>> --- >>> >>> 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 <[email protected]> > > Thanks to you too for the review :) >
Please hold on this patch. I took another look at this and spotted unfortunate typo in the tests that I wrote and indeed wraparound happens before EOC bit is set, just like Ben told :( I'll be looking at this all again during next days. Looks like the EOC bit is set after a burst completion once hardware counter is reloaded.
