[4/6] dma: tegra: add accurate reporting of dma state
diff mbox series

Message ID 20181012094454.22841-5-ben.dooks@codethink.co.uk
State Superseded
Headers show
Series
  • [1/6] dma: tegra: avoid overflow of byte tracking
Related show

Commit Message

Ben Dooks Oct. 12, 2018, 9:44 a.m. UTC
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@codethink.co.uk>
---
 drivers/dma/tegra20-apb-dma.c | 92 ++++++++++++++++++++++++++++++++---
 1 file changed, 86 insertions(+), 6 deletions(-)

Comments

kernel test robot Oct. 12, 2018, 9:47 p.m. UTC | #1
Hi Ben,

I love your patch! Perhaps something to improve:

[auto build test WARNING on sof-driver-fuweitax/master]
[also build test WARNING on v4.19-rc7 next-20181012]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Ben-Dooks/dma-tegra-avoid-overflow-of-byte-tracking/20181013-023951
base:   https://github.com/fuweitax/linux master
config: arm-allmodconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=arm 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   In file included from include/linux/printk.h:332:0,
                    from include/linux/kernel.h:14,
                    from include/linux/clk.h:16,
                    from drivers//dma/tegra20-apb-dma.c:20:
   drivers//dma/tegra20-apb-dma.c: In function 'tegra_dma_tx_status':
   include/linux/dynamic_debug.h:135:3: warning: 'done' may be used uninitialized in this function [-Wmaybe-uninitialized]
      __dynamic_dev_dbg(&descriptor, dev, fmt, \
      ^~~~~~~~~~~~~~~~~
   drivers//dma/tegra20-apb-dma.c:816:6: note: 'done' was declared here
     int done;
         ^~~~
   In file included from include/linux/printk.h:332:0,
                    from include/linux/kernel.h:14,
                    from include/linux/clk.h:16,
                    from drivers//dma/tegra20-apb-dma.c:20:
   include/linux/dynamic_debug.h:135:3: warning: 'wcount' may be used uninitialized in this function [-Wmaybe-uninitialized]
      __dynamic_dev_dbg(&descriptor, dev, fmt, \
      ^~~~~~~~~~~~~~~~~
   drivers//dma/tegra20-apb-dma.c:811:16: note: 'wcount' was declared here
     unsigned long wcount;
                   ^~~~~~
>> drivers//dma/tegra20-apb-dma.c:843:30: warning: 'sg_req' may be used uninitialized in this function [-Wmaybe-uninitialized]
       result = residual - sg_req->req_len;
                           ~~~~~~^~~~~~~~~
   drivers//dma/tegra20-apb-dma.c:894:27: note: 'sg_req' was declared here
     struct tegra_dma_sg_req *sg_req;
                              ^~~~~~

vim +/sg_req +843 drivers//dma/tegra20-apb-dma.c

   804	
   805	static unsigned int tegra_dma_update_residual(struct tegra_dma_channel *tdc,
   806						      struct tegra_dma_sg_req *sg_req,
   807						      struct tegra_dma_desc *dma_desc,
   808						      unsigned int residual)
   809	{
   810		unsigned long status = 0x0;
   811		unsigned long wcount;
   812		unsigned long ahbptr;
   813		unsigned long tmp = 0x0;
   814		unsigned int result;
   815		int retries = TEGRA_APBDMA_BURST_COMPLETE_TIME * 10;
   816		int done;
   817	
   818		/* if we're not the current request, then don't alter the residual */
   819		if (sg_req != list_first_entry(&tdc->pending_sg_req,
   820					       struct tegra_dma_sg_req, node)) {
   821			result = residual;
   822			ahbptr = 0xffffffff;
   823			goto done;
   824		}
   825	
   826		/* loop until we have a reliable result for residual */
   827		do {
   828			ahbptr = tdc_read(tdc, TEGRA_APBDMA_CHAN_AHBPTR);
   829			status = tdc_read(tdc, TEGRA_APBDMA_CHAN_STATUS);
   830			tmp =  tdc_read(tdc, 0x08);	/* total count for debug */
   831	
   832			/* check status, if channel isn't busy then skip */
   833			if (!(status & TEGRA_APBDMA_STATUS_BUSY)) {
   834				result = residual;
   835				break;
   836			}
   837	
   838			/* if we've got an interrupt pending on the channel, don't
   839			 * try and deal with the residue as the hardware has likely
   840			 * moved on to the next buffer. return all data moved.
   841			 */
   842			if (status & TEGRA_APBDMA_STATUS_ISE_EOC) {
 > 843				result = residual - sg_req->req_len;
   844				break;
   845			}
   846	
   847			if (tdc->tdma->chip_data->support_separate_wcount_reg)
   848				wcount = tdc_read(tdc, TEGRA_APBDMA_CHAN_WORD_TRANSFER);
   849			else
   850				wcount = status;
   851	
   852			/* If the request is at the full point, then there is a
   853			 * chance that we have read the status register in the
   854			 * middle of the hardware reloading the next buffer.
   855			 *
   856			 * The sequence seems to be at the end of the buffer, to
   857			 * load the new word count before raising the EOC flag (or
   858			 * changing the ping-pong flag which could have also been
   859			 * used to determine a new buffer). This  means there is a
   860			 * small window where we cannot determine zero-done for the
   861			 * current buffer, or moved to next buffer.
   862			 *
   863			 * If done shows 0, then retry the load, as it may hit the
   864			 * above hardware race. We will either get a new value which
   865			 * is from the first buffer, or we get an EOC (new buffer)
   866			 * or both a new value and an EOC...
   867			 */
   868			done = get_current_xferred_count(tdc, sg_req, wcount);
   869			if (done != 0) {
   870				result = residual - done;
   871				break;
   872			}
   873	
   874			ndelay(100);
   875		} while (--retries > 0);
   876	
   877		if (retries <= 0) {
   878			dev_err(tdc2dev(tdc), "timeout waiting for dma load\n");
   879			result = residual;
   880		}
   881	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Patch
diff mbox series

diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
index 4f7d1e576d03..ce2888f67254 100644
--- a/drivers/dma/tegra20-apb-dma.c
+++ b/drivers/dma/tegra20-apb-dma.c
@@ -802,6 +802,90 @@  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)
 {
@@ -843,6 +927,7 @@  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);
 	}
 
@@ -1436,12 +1521,7 @@  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;