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

[Sowjanya Komatineni]

> >>>> 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?
> >>
> >> I tried to enforce DMA without changing bursts:
> >>
> >> ----------
> >> diff --git a/drivers/i2c/busses/i2c-tegra.c 
> >> b/drivers/i2c/busses/i2c-tegra.c index c538ed5f8e2c..5d1c54ce7800 
> >> 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>
> >> @@ -1046,8 +1048,7 @@ 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;
> >> ----------
> >>
> >> Here is the log with this change:
> >>
> >> [    0.760796] tegra_rtc 7000e000.rtc: registered as rtc1
> >> [    0.760850] tegra_rtc 7000e000.rtc: Tegra internal Real Time Clock
> >> [    0.761050] i2c /dev entries driver
> >> [    0.918928] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> >> [    0.918940] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.919040] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    0.919050] tegra-i2c 7000c000.i2c: starting DMA for length: 8
> >> [    0.919059] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.919322] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    0.919335] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> >> [    0.919343] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.919440] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    0.919448] tegra-i2c 7000c000.i2c: starting DMA for length: 112
> >> [    0.919456] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.922818] tegra-i2c 7000c000.i2c: transfer complete: 11 0 0
> >> [    0.922829] atmel_mxt_ts 0-004c: Family: 160 Variant: 0 Firmware V1.0.AA Objects: 18
> >> [    0.922886] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> >> [    0.922895] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.922993] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    0.923002] tegra-i2c 7000c000.i2c: starting DMA for length: 224
> >> [    0.923011] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.933253] tegra-i2c 7000c000.i2c: transfer complete: 11 0 0
> >> [    0.933287] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> >> [    0.933297] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.933478] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    0.933487] tegra-i2c 7000c000.i2c: starting DMA for length: 12
> >> [    0.933496] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    0.945120] tegra-i2c 7000d000.i2c: starting DMA for length: 16
> >> [    0.945130] tegra-i2c 7000d000.i2c: unmasked irq: 0c
> >> [    1.038917] tegra-i2c 7000c000.i2c: DMA transfer timeout
> >> [    1.038982] atmel_mxt_ts 0-004c: __mxt_read_reg: i2c transfer failed (-110)
> >> [    1.039000] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> >> [    1.039006] atmel_mxt_ts 0-004c: Failed to read T44 and T5 (-110)



> >> [    1.039009] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    1.039148] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    1.039157] tegra-i2c 7000c000.i2c: starting DMA for length: 4
> >> [    1.039166] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    1.039304] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    1.039340] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> >> [    1.039349] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    1.039535] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    1.039544] tegra-i2c 7000c000.i2c: starting DMA for length: 12
> >> [    1.039552] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    1.040055] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    1.040083] tegra-i2c 7000c000.i2c: starting DMA for length: 16
> >> [    1.040092] tegra-i2c 7000c000.i2c: unmasked irq: 0c
> >> [    1.040301] tegra-i2c 7000c000.i2c: transfer complete: 10 0 0
> >> [    1.048934] tegra-i2c 7000d000.i2c: i2c transfer timed out
> > 
> > This log shows DMA transfer timeout for atmel read.
> > Do you see issue if you donât enforce dma all time and let it choose PIO Vs DMA?
> > 
> 
> No, there are no timeout errors in PIO mode. I could post full log with the PIO-only mode if you want.
>
Yes please post full log of PIO only and DMA only