Re: [PATCH v2] dmaengine: tegra-apb: Support per-burst residue granularity

Jon Hunter
2019-06-20T08:38:59Z

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@codethink.co.uk/
> Inspired-by: Ben Dooks <ben.dooks@codethink.co.uk>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
>
> 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@nvidia.com>

Cheers
Jon

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nvpublic