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

Dmitry Osipenko
2019-06-20T21:58:58Z

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/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>

Thanks to you too for the review :)