dmaengine Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH v5] dmaengine: tegra-apb: Support per-burst residue granularity
@ 2019-07-05 15:05 Dmitry Osipenko
  2019-07-25 10:26 ` Vinod Koul
  0 siblings, 1 reply; 3+ messages in thread
From: Dmitry Osipenko @ 2019-07-05 15:05 UTC (permalink / raw)
  To: Laxman Dewangan, Vinod Koul, Thierry Reding, Jonathan Hunter, Ben Dooks
  Cc: dmaengine, linux-tegra, linux-kernel

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 chromium web browser. The patch is
based on the original work that was made by Ben Dooks and a patch from
downstream kernel. It was tested on Tegra20 and Tegra30 devices.

Link: https://lore.kernel.org/lkml/20190424162348.23692-1-ben.dooks@codethink.co.uk/
Link: https://nv-tegra.nvidia.com/gitweb/?p=linux-4.4.git;a=commit;h=c7bba40c6846fbf3eaad35c4472dcc7d8bbc02e5
Inspired-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---

Changelog:

v5: Adjusted the code's comment as was suggested by Jon Hunter in the
    review comment to v4.

v4: The words_xferred is now also reset on a new iteration of a cyclic
    transfer by ISR, so that dmaengine_tx_status() won't produce a
    misleading warning splat on TX status re-checking after a cycle
    completion when cyclic transfer consists of a single SG.

v3: Added workaround for a hardware design shortcoming that results
    in a words counter wraparound before end-of-transfer bit is set
    in a cyclic mode.

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 | 75 +++++++++++++++++++++++++++++++----
 1 file changed, 68 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
index 79e9593815f1..3a45079d11ec 100644
--- a/drivers/dma/tegra20-apb-dma.c
+++ b/drivers/dma/tegra20-apb-dma.c
@@ -152,6 +152,7 @@ struct tegra_dma_sg_req {
 	bool				last_sg;
 	struct list_head		node;
 	struct tegra_dma_desc		*dma_desc;
+	unsigned int			words_xferred;
 };
 
 /*
@@ -496,6 +497,7 @@ static void tegra_dma_configure_for_next(struct tegra_dma_channel *tdc,
 	tdc_write(tdc, TEGRA_APBDMA_CHAN_CSR,
 				nsg_req->ch_regs.csr | TEGRA_APBDMA_CSR_ENB);
 	nsg_req->configured = true;
+	nsg_req->words_xferred = 0;
 
 	tegra_dma_resume(tdc);
 }
@@ -511,6 +513,7 @@ static void tdc_start_head_req(struct tegra_dma_channel *tdc)
 					typeof(*sg_req), node);
 	tegra_dma_start(tdc, sg_req);
 	sg_req->configured = true;
+	sg_req->words_xferred = 0;
 	tdc->busy = true;
 }
 
@@ -638,6 +641,8 @@ static void handle_cont_sngl_cycle_dma_done(struct tegra_dma_channel *tdc,
 		list_add_tail(&dma_desc->cb_node, &tdc->cb_desc);
 	dma_desc->cb_count++;
 
+	sgreq->words_xferred = 0;
+
 	/* If not last req then put at end of pending list */
 	if (!list_is_last(&sgreq->node, &tdc->pending_sg_req)) {
 		list_move_tail(&sgreq->node, &tdc->pending_sg_req);
@@ -797,6 +802,65 @@ 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;
+
+	wcount = get_current_xferred_count(tdc, sg_req, wcount);
+
+	if (!wcount) {
+		/*
+		 * If wcount wasn't ever polled for this SG before, then
+		 * simply assume that transfer hasn't started yet.
+		 *
+		 * Otherwise it's the end of the transfer.
+		 *
+		 * The alternative would be to poll the status register
+		 * until EOC bit is set or wcount goes UP. That's so
+		 * because EOC bit is getting set only after the last
+		 * burst's completion and counter is less than the actual
+		 * transfer size by 4 bytes. The counter value wraps around
+		 * in a cyclic mode before EOC is set(!), so we can't easily
+		 * distinguish start of transfer from its end.
+		 */
+		if (sg_req->words_xferred)
+			wcount = sg_req->req_len - 4;
+
+	} else if (wcount < sg_req->words_xferred) {
+		/*
+		 * This case will never happen for a non-cyclic transfer.
+		 *
+		 * For a cyclic transfer, although it is possible for the
+		 * next transfer to have already started (resetting the word
+		 * count), this case should still not happen because we should
+		 * have detected that the EOC bit is set and hence the transfer
+		 * was completed.
+		 */
+		WARN_ON_ONCE(1);
+
+		wcount = sg_req->req_len - 4;
+	} else {
+		sg_req->words_xferred = wcount;
+	}
+
+	return wcount;
+}
+
 static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
 	dma_cookie_t cookie, struct dma_tx_state *txstate)
 {
@@ -806,6 +870,7 @@ 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 +890,7 @@ 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 +902,7 @@ 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 +1507,7 @@ 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;
-- 
2.22.0


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v5] dmaengine: tegra-apb: Support per-burst residue granularity
  2019-07-05 15:05 [PATCH v5] dmaengine: tegra-apb: Support per-burst residue granularity Dmitry Osipenko
@ 2019-07-25 10:26 ` Vinod Koul
  2019-07-25 13:44   ` Dmitry Osipenko
  0 siblings, 1 reply; 3+ messages in thread
From: Vinod Koul @ 2019-07-25 10:26 UTC (permalink / raw)
  To: Dmitry Osipenko
  Cc: Laxman Dewangan, Thierry Reding, Jonathan Hunter, Ben Dooks,
	dmaengine, linux-tegra, linux-kernel

On 05-07-19, 18:05, 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 chromium web browser. The patch is
> based on the original work that was made by Ben Dooks and a patch from
> downstream kernel. It was tested on Tegra20 and Tegra30 devices.

Applied, thanks

-- 
~Vinod

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v5] dmaengine: tegra-apb: Support per-burst residue granularity
  2019-07-25 10:26 ` Vinod Koul
@ 2019-07-25 13:44   ` Dmitry Osipenko
  0 siblings, 0 replies; 3+ messages in thread
From: Dmitry Osipenko @ 2019-07-25 13:44 UTC (permalink / raw)
  To: Vinod Koul
  Cc: Laxman Dewangan, Thierry Reding, Jonathan Hunter, Ben Dooks,
	dmaengine, linux-tegra, linux-kernel

25.07.2019 13:26, Vinod Koul пишет:
> On 05-07-19, 18:05, 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 chromium web browser. The patch is
>> based on the original work that was made by Ben Dooks and a patch from
>> downstream kernel. It was tested on Tegra20 and Tegra30 devices.
> 
> Applied, thanks
> 

Thanks!

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, back to index

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-07-05 15:05 [PATCH v5] dmaengine: tegra-apb: Support per-burst residue granularity Dmitry Osipenko
2019-07-25 10:26 ` Vinod Koul
2019-07-25 13:44   ` Dmitry Osipenko

dmaengine Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/dmaengine/0 dmaengine/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dmaengine dmaengine/ https://lore.kernel.org/dmaengine \
		dmaengine@vger.kernel.org dmaengine@archiver.kernel.org
	public-inbox-index dmaengine


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.dmaengine


AGPL code for this site: git clone https://public-inbox.org/ public-inbox