dma: tegra: add accurate reporting of dma state
PATCH 4/6 dma: tegra: add accurate reporting of dma state
Quoted 82 lines · Ben Dooks
Quoted 34 lines · Dmitry Osipenko
Quoted 5 lines · Ben Dooks
The
tx_statuscallback 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.Quoted 7 lines
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 <[email protected]>Hello Ben,
Thank you very much for the patch! It fixes "farting sound" for chromium-browser and applications that use chromium-engine (tested on Tegra20) because apparently it tries to use low latency for everything and audio buffer is constantly underflowing without more detailed DMA-progress reporting. See couple more comments below.
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---
drivers/dma/tegra20-apb-dma.c | 94 ++++++++++++++++++++++++++++++++---1 file changed, 87 insertions(+), 7 deletions(-)drivers/dma/tegra20-apb-dma.c +0
-0@@ -802,12 +802,96 @@ static int tegra_dma_terminate_all(struct dma_chan *dc) return 0; }Quoted 8 lines
drivers/dma/tegra20-apb-dma.c static int tegra_dma_terminate_all(struct dma_chan *dc) · line 810
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drivers/dma/tegra20-apb-dma.c +6
-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;There is no need to initialize "status" variable.
ok, will check this.
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drivers/dma/tegra20-apb-dma.c +19
-0+ 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);Quoted 4 lines
drivers/dma/tegra20-apb-dma.c static int tegra_dma_terminate_all(struct dma_chan *dc) · line 830
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drivers/dma/tegra20-apb-dma.c +1
-0+ tmp = tdc_read(tdc, 0x08); /* total count for debug */Register
0x08(DMA_BYTE_STA) doesn't present on Tegra20 and "tmp" isn't used anywhere in the code. Please remove it entirely.ok, fixed
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drivers/dma/tegra20-apb-dma.c +6
-0+ + /* check status, if channel isn't busy then skip */ + if (!(status & TEGRA_APBDMA_STATUS_BUSY)) { + result = residual; + break; + }
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If "BUSY" is unset, doesn't this mean that transaction could be completed already? I don't quite understand why you want to skip here.
I can't remember what the reasoning behind this was, this work was originally done over a year ago and I am not sure if I can find any of the notes from this.
Looks like it should be safe to remove this hunk. Please consider the removal or provide reasoning in the comment to the code if you'll recall it.
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drivers/dma/tegra20-apb-dma.c +13
-0+ + /* 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); + elsedrivers/dma/tegra20-apb-dma.c static int tegra_dma_terminate_all(struct dma_chan *dc) · line 859
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drivers/dma/tegra20-apb-dma.c +10
-0+ 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 two whitespaces here-----|
Quoted 8 lines
drivers/dma/tegra20-apb-dma.c +7
-0+ * 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...
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I think we just need to wait 20usec after reading out "words count" and then re-check interrupt status, so transfer is done if interrupt is set and otherwise "words count" value is actual and reliable.
At the moment I have no way of going back and re-testing this code against the problem it originally fixed, so would rather not change the algorithm in this.
Please tell what was the problem.
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drivers/dma/tegra20-apb-dma.c static int tegra_dma_terminate_all(struct dma_chan *dc) · line 875
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drivers/dma/tegra20-apb-dma.c +8
-0+*/ + done = get_current_xferred_count(tdc, sg_req, wcount); + if (done != 0) { + result = residual - done; + break; + } + + ndelay(100);Quoted 2 lines
There is no
ndelay()on ARM, hence your 20usec timeout is 200usec. Please useudelay().I thought there was one based on the lpj calculations, I will check later.
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drivers/dma/tegra20-apb-dma.c static int tegra_dma_terminate_all(struct dma_chan *dc) · line 883
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drivers/dma/tegra20-apb-dma.c +8
-0+ } while (--retries > 0); + + if (retries <= 0) { + dev_err(tdc2dev(tdc), "timeout waiting for dma load\n"); + result = residual; + } + +done:Please rename goto label as it duplicates local variable name.
ok, fixed.
Quoted 16 lines
drivers/dma/tegra20-apb-dma.c static int tegra_dma_terminate_all(struct dma_chan *dc) · line 885
Quoted 2 lines
drivers/dma/tegra20-apb-dma.c +2
-0+ dev_dbg(tdc2dev(tdc), "residual: req %08lx, ahb@%08lx, wcount %08lx, done %d\n", + sg_req->ch_regs.ahb_ptr, ahbptr, wcount, done);Whitespace just after tab not needed.
Quoted 11 lines
drivers/dma/tegra20-apb-dma.c +5
-1+ + return result; +} + static enum dma_status tegra_dma_tx_status(struct dma_chan *dc, dma_cookie_t cookie, struct dma_tx_state *txstate) { struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc); struct tegra_dma_desc *dma_desc; - struct tegra_dma_sg_req *sg_req; + struct tegra_dma_sg_req *sg_req = NULL;
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drivers/dma/tegra20-apb-dma.c +0
-0enum dma_status ret; unsigned long flags;unsigned int residual;
drivers/dma/tegra20-apb-dma.c +0
-0@@ -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);
Line over 80 characters. Please make sure that "scripts/checkpatch.pl" doesn't have valid complains about the patches.
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