Re: [PATCH] dma: tegra: add accurate reporting of dma state

[Jon Hunter]

On 24/04/2019 17:23, Ben Dooks wrote:
> The tx_status callback does not report the state of the transfer
> beyond complete segments. This causes problems with users such as
> ALSA when applications want to know accurately how much data has
> been moved.
> 
> This patch addes a function tegra_dma_update_residual() to query
> the hardware and modify the residual information accordinly. It
> takes into account any hardware issues when trying to read the
> state, such as delays between finishing a buffer and signalling
> the interrupt.
> 
> Signed-off-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>
> ---
> Cc: Dmitry Osipenko <digetx@xxxxxxxxx>
> Cc: Laxman Dewangan <ldewangan@xxxxxxxxxx> (supporter:TEGRA DMA DRIVERS)
> Cc: Jon Hunter <jonathanh@xxxxxxxxxx> (supporter:TEGRA DMA DRIVERS)
> Cc: Vinod Koul <vkoul@xxxxxxxxxx> (maintainer:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM)
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> (reviewer:ASYNCHRONOUS TRANSFERS/TRANSFORMS (IOAT) API)
> Cc: Thierry Reding <thierry.reding@xxxxxxxxx> (supporter:TEGRA ARCHITECTURE SUPPORT)
> Cc: dmaengine@xxxxxxxxxxxxxxx (open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM)
> Cc: linux-tegra@xxxxxxxxxxxxxxx (open list:TEGRA ARCHITECTURE SUPPORT)
> Cc: linux-kernel@xxxxxxxxxxxxxxx (open list)
> ---
>  drivers/dma/tegra20-apb-dma.c | 92 ++++++++++++++++++++++++++++++++---
>  1 file changed, 86 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> index cf462b1abc0b..544e7273e741 100644
> --- a/drivers/dma/tegra20-apb-dma.c
> +++ b/drivers/dma/tegra20-apb-dma.c
> @@ -808,6 +808,90 @@ 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 = 0x0;
> +	unsigned long wcount;
> +	unsigned long ahbptr;
> +	unsigned long tmp = 0x0;
> +	unsigned int result;
> +	int retries = TEGRA_APBDMA_BURST_COMPLETE_TIME * 10;
> +	int done;
> +
> +	/* if we're not the current request, then don't alter the residual */
> +	if (sg_req != list_first_entry(&tdc->pending_sg_req,
> +				       struct tegra_dma_sg_req, node)) {
> +		result = residual;
> +		ahbptr = 0xffffffff;
> +		goto done;
> +	}
> +
> +	/* loop until we have a reliable result for residual */
> +	do {
> +		ahbptr = tdc_read(tdc, TEGRA_APBDMA_CHAN_AHBPTR);
> +		status = tdc_read(tdc, TEGRA_APBDMA_CHAN_STATUS);
> +		tmp =  tdc_read(tdc, 0x08);	/* total count for debug */
> +
> +		/* check status, if channel isn't busy then skip */
> +		if (!(status & TEGRA_APBDMA_STATUS_BUSY)) {
> +			result = residual;
> +			break;
> +		}
> +
> +		/* if we've got an interrupt pending on the channel, don't
> +		 * try and deal with the residue as the hardware has likely
> +		 * moved on to the next buffer. return all data moved.
> +		 */
> +		if (status & TEGRA_APBDMA_STATUS_ISE_EOC) {
> +			result = residual - sg_req->req_len;
> +			break;
> +		}
> +
> +		if (tdc->tdma->chip_data->support_separate_wcount_reg)
> +			wcount = tdc_read(tdc, TEGRA_APBDMA_CHAN_WORD_TRANSFER);
> +		else
> +			wcount = status;
> +
> +		/* If the request is at the full point, then there is a
> +		 * chance that we have read the status register in the
> +		 * middle of the hardware reloading the next buffer.
> +		 *
> +		 * The sequence seems to be at the end of the buffer, to
> +		 * load the new word count before raising the EOC flag (or
> +		 * changing the ping-pong flag which could have also been
> +		 * used to determine a new buffer). This  means there is a
> +		 * small window where we cannot determine zero-done for the
> +		 * current buffer, or moved to next buffer.
> +		 *
> +		 * If done shows 0, then retry the load, as it may hit the
> +		 * above hardware race. We will either get a new value which
> +		 * is from the first buffer, or we get an EOC (new buffer)
> +		 * or both a new value and an EOC...
> +		 */
> +		done = get_current_xferred_count(tdc, sg_req, wcount);
> +		if (done != 0) {
> +			result = residual - done;
> +			break;
> +		}
> +
> +		ndelay(100);
> +	} while (--retries > 0);
> +
> +	if (retries <= 0) {
> +		dev_err(tdc2dev(tdc), "timeout waiting for dma load\n");
> +		result = residual;
> +	}
> +
> +done:	
> +	dev_dbg(tdc2dev(tdc), "residual: req %08lx, ahb@%08lx, wcount %08lx, done %d\n",
> +		 sg_req->ch_regs.ahb_ptr, ahbptr, wcount, done);
> +
> +	return result;
> +}
> +
>  static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
>  	dma_cookie_t cookie, struct dma_tx_state *txstate)
>  {
> @@ -849,6 +933,7 @@ 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);
>  		dma_set_residue(txstate, residual);
>  	}
>  
> @@ -1444,12 +1529,7 @@ 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;

In addition to Dmitry's comments, can you please make sure you run this
through checkpatch.pl?

Thanks
Jon

-- 
nvpublic