Re: [PATCH V12 3/5] i2c: tegra: Add DMA support

From: Thierry Reding
Date: Wed Feb 06 2019 - 08:13:18 EST

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On Wed, Feb 06, 2019 at 02:09:09PM +0100, Thierry Reding wrote:
> On Wed, Feb 06, 2019 at 02:55:01PM +0300, Dmitry Osipenko wrote:
[...]
> > Sowjanya, I tried to enforce DMA transferring + setting DMA burst to a one word and this combination doesn't work well while it should, if I'm not missing something. Could you please take a look at the problem or explain why that happens?
> >
> > Here is the change I made:
> >
> > -----------------
> > diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> > index c538ed5f8e2c..59e245d4417d 100644
> > --- a/drivers/i2c/busses/i2c-tegra.c
> > +++ b/drivers/i2c/busses/i2c-tegra.c
> > @@ -6,6 +6,8 @@
> > * Author: Colin Cross <ccross@xxxxxxxxxxx>
> > */
> >
> > +#define DEBUG
> > +
> > #include <linux/clk.h>
> > #include <linux/delay.h>
> > #include <linux/dmaengine.h>
> > @@ -929,12 +931,7 @@ static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
> > val = i2c_readl(i2c_dev, reg);
> >
> > if (i2c_dev->is_curr_dma_xfer) {
> > - if (len & 0xF)
> > dma_burst = 1;
> > - else if (len & 0x10)
> > - dma_burst = 4;
> > - else
> > - dma_burst = 8;
> >
> > if (i2c_dev->msg_read) {
> > chan = i2c_dev->rx_dma_chan;
> > @@ -1046,8 +1043,7 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
> > xfer_size = msg->len + I2C_PACKET_HEADER_SIZE;
> >
> > xfer_size = ALIGN(xfer_size, BYTES_PER_FIFO_WORD);
> > - i2c_dev->is_curr_dma_xfer = (xfer_size > I2C_PIO_MODE_MAX_LEN) &&
> > - i2c_dev->dma_buf;
> > + i2c_dev->is_curr_dma_xfer = !!i2c_dev->dma_buf;
> > tegra_i2c_config_fifo_trig(i2c_dev, xfer_size);
> > dma = i2c_dev->is_curr_dma_xfer
> > -----------------
> >
> > And here what happens:
> >
> > -----------------
> > ...
> > [ 0.761144] tegra_rtc 7000e000.rtc: registered as rtc1
> > [ 0.761199] tegra_rtc 7000e000.rtc: Tegra internal Real Time Clock
> > [ 0.761406] i2c /dev entries driver
> > [ 0.919233] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.919246] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.919345] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.919355] tegra-i2c 7000c000.i2c: starting DMA for length: 8
> > [ 0.919363] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.919628] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.919641] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.919649] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.919746] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.919755] tegra-i2c 7000c000.i2c: starting DMA for length: 112
> > [ 0.919763] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.923140] tegra-i2c 7000c000.i2c: transfer complete: 11 0 0
> > [ 0.923150] atmel_mxt_ts 0-004c: Family: 160 Variant: 0 Firmware V1.0.AA Objects: 18
> > [ 0.923208] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.923217] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.923314] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.923323] tegra-i2c 7000c000.i2c: starting DMA for length: 224
> > [ 0.923331] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.933564] tegra-i2c 7000c000.i2c: transfer complete: 11 0 0
> > [ 0.933599] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.933609] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.933760] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.933770] tegra-i2c 7000c000.i2c: starting DMA for length: 12
> > [ 0.933779] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.934284] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.934309] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.934317] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.934500] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.934509] tegra-i2c 7000c000.i2c: starting DMA for length: 12
> > [ 0.934518] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.935023] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.935081] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.935091] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.935240] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.935249] tegra-i2c 7000c000.i2c: starting DMA for length: 4
> > [ 0.935258] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.935399] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.935416] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.935424] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.935655] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.945445] tegra-i2c 7000d000.i2c: starting DMA for length: 16
> > [ 0.945456] tegra-i2c 7000d000.i2c: unmasked irq: 0c
> > [ 0.969236] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.969245] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.969361] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.969370] tegra-i2c 7000c000.i2c: starting DMA for length: 4
> > [ 0.969379] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.969462] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.982587] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.982596] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.982722] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.982731] tegra-i2c 7000c000.i2c: starting DMA for length: 12
> > [ 0.982740] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.983071] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.983090] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.983098] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.983252] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.983261] tegra-i2c 7000c000.i2c: starting DMA for length: 136
> > [ 0.983269] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.987605] tegra-i2c 7000c000.i2c: transfer complete: 11 0 0
> > [ 0.987623] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 0.987631] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.987800] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 0.987809] tegra-i2c 7000c000.i2c: starting DMA for length: 12
> > [ 0.987817] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 0.988324] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 1.009227] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 1.009236] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 1.009374] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 1.009383] tegra-i2c 7000c000.i2c: starting DMA for length: 4
> > [ 1.009391] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 1.009479] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 1.009497] atmel_mxt_ts 0-004c: Warning: Info CRC error - device=0xF436DC file=0x000000
> > [ 1.009588] tegra-i2c 7000c000.i2c: starting DMA for length: 272
> > [ 1.009597] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 1.017483] tegra-i2c 7000c000.i2c: transfer complete: 11 0 0
> > [ 1.017496] tegra-i2c 7000c000.i2c: starting DMA for length: 120
> > [ 1.017504] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 1.020896] tegra-i2c 7000c000.i2c: transfer complete: 11 0 0
> > [ 1.020909] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 1.020918] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 1.021055] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 1.032230] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> > [ 1.032239] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 1.032359] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 1.032368] tegra-i2c 7000c000.i2c: starting DMA for length: 12
> > [ 1.032376] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> > [ 1.032704] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> > [ 1.049224] tegra-i2c 7000d000.i2c: i2c transfer timed out
>
> That's odd because it suggests that DMA actually completed, but the
> message didn't.
>
> I'm not sure I understand how that could happen.
>
> What's also weird above is that there doesn't seem to be a DMA that
> is started for that particular message. Or is the timeout message a
> response to the prior transfer (length 10)? Seems like that should
> not be possible because we get the "transfer complete" message.

Wait, those are actually different instances of the I2C controller, so
the relevant log entries are these:

[ 0.945445] tegra-i2c 7000d000.i2c: starting DMA for length: 16
[ 0.945456] tegra-i2c 7000d000.i2c: unmasked irq: 0c
...
[ 1.049224] tegra-i2c 7000d000.i2c: i2c transfer timed out

And these don't happen if you use higher burst sizes or before the DMA
series?

Thierry

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Next message: Luiz Capitulino: "Re: [RFC][Patch v8 5/7] virtio: Enables to add a single descriptor to the host"
Previous message: Chen-Yu Tsai: "Re: [PATCH 5/5] arm: dts: axpxx: add charge led node"
In reply to: Thierry Reding: "Re: [PATCH V12 3/5] i2c: tegra: Add DMA support"
Next in thread: Dmitry Osipenko: "Re: [PATCH V12 3/5] i2c: tegra: Add DMA support"
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