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Date: Wed, 1 May 2019 09:33:31 +0100
From: Jon Hunter <jonathanh@...dia.com>
To: Ben Dooks <ben.dooks@...ethink.co.uk>,
<linux-kernel@...ts.codethink.co.uk>
CC: Dmitry Osipenko <digetx@...il.com>,
Laxman Dewangan <ldewangan@...dia.com>,
Vinod Koul <vkoul@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
Thierry Reding <thierry.reding@...il.com>,
<dmaengine@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dma: tegra: add accurate reporting of dma state
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@...ethink.co.uk>
> ---
> Cc: Dmitry Osipenko <digetx@...il.com>
> Cc: Laxman Dewangan <ldewangan@...dia.com> (supporter:TEGRA DMA DRIVERS)
> Cc: Jon Hunter <jonathanh@...dia.com> (supporter:TEGRA DMA DRIVERS)
> Cc: Vinod Koul <vkoul@...nel.org> (maintainer:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM)
> Cc: Dan Williams <dan.j.williams@...el.com> (reviewer:ASYNCHRONOUS TRANSFERS/TRANSFORMS (IOAT) API)
> Cc: Thierry Reding <thierry.reding@...il.com> (supporter:TEGRA ARCHITECTURE SUPPORT)
> Cc: dmaengine@...r.kernel.org (open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM)
> Cc: linux-tegra@...r.kernel.org (open list:TEGRA ARCHITECTURE SUPPORT)
> Cc: linux-kernel@...r.kernel.org (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@...lx, 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
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