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

From: Thierry Reding
Date: Wed Feb 06 2019 - 08:09:18 EST

On Wed, Feb 06, 2019 at 02:55:01PM +0300, Dmitry Osipenko wrote:
> 06.02.2019 1:46, Sowjanya Komatineni ÐÐÑÐÑ:
> > This patch adds DMA support for Tegra I2C.
> >
> > Tegra I2C TX and RX FIFO depth is 8 words. PIO mode is used for
> > transfer size of the max FIFO depth and DMA mode is used for
> > transfer size higher than max FIFO depth to save CPU overhead.
> >
> > PIO mode needs full intervention of CPU to fill or empty FIFO's
> > and also need to service multiple data requests interrupt for the
> > same transaction. This adds delay between data bytes of the same
> > transfer when CPU is fully loaded and some slave devices has
> > internal timeout for no bus activity and stops transaction to
> > avoid bus hang. DMA mode is helpful in such cases.
> >
> > DMA mode is also helpful for Large transfers during downloading or
> > uploading FW over I2C to some external devices.
> >
> > Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
> > ---
> > [V12] : Replaced dma_alloc_coherent with dma_alloc_attrs to force the allocated
> > buffer to be contiguous also in physical memory as Tegra194 supports max
> > 64K and dma_alloc_coherent doesnt guarentee contiguous memory.
> > Changed return code from EIO to EINVAL incase of failure to obtain dma
> > descriptor.
> > Fixed coding style check issues.
> > [V11] : Replaced deprecated dmaengine_terminate_all with dmaengine_termine_async
> > from non-atomic context and dmaengine_terminate_sync from atomic context.
> > Fixed to program fifo trigger levels properly when transfer falls back to
> > pio mode in case of dma slave configuration failure and other minor fixes.
> > [V10] : APBDMA is replaced with GPCDMA on Tegra186 and Tegra194 designs.
> > Added apbdma hw support flag to now allow Tegra186 and later use
> > APBDMA driver.
> > Added explicit flow control enable for DMA slave config and error handling.
> > Moved releasing DMA resources to seperate function to reuse in
> > multiple places.
> > Updated to register tegra_i2c_driver from module level rather than subsys
> > level.
> > Other minor feedback
> > [V9] : Rebased to 5.0-rc4
> > Removed dependency of APB DMA in Kconfig and added conditional check
> > in I2C driver to decide on using DMA mode.
> > Changed back the allocation of dma buffer during i2c probe.
> > Fixed FIFO triggers depending on DMA Vs PIO.
> > [V8] : Moved back dma init to i2c probe, removed ALL_PACKETS_XFER_COMPLETE
> > interrupt and using PACKETS_XFER_COMPLETE interrupt only and some
> > other fixes
> > Updated Kconfig for APB_DMA dependency
> > [V7] : Same as V6
> > [V6] : Updated for proper buffer allocation/freeing, channel release.
> > Updated to use exact xfer size for syncing dma buffer.
> > [V5] : Same as V4
> > [V4] : Updated to allocate DMA buffer only when DMA mode.
> > Updated to fall back to PIO mode when DMA channel request or
> > buffer allocation fails.
> > [V3] : Updated without additional buffer allocation.
> > [V2] : Updated based on V1 review feedback along with code cleanup for
> > proper implementation of DMA.
> >
> >
> > drivers/i2c/busses/i2c-tegra.c | 413 ++++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 369 insertions(+), 44 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> > index 118b7023a0f4..77277a09e485 100644
> > --- a/drivers/i2c/busses/i2c-tegra.c
> > +++ b/drivers/i2c/busses/i2c-tegra.c
> > @@ -8,6 +8,9 @@
> >
> > #include <linux/clk.h>
> > #include <linux/delay.h>
> > +#include <linux/dmaengine.h>
> > +#include <linux/dmapool.h>
>
> We are not using DMA pools anywhere in the code, <linux/dmapool.h> isn't needed. Let's remove it.
>
> > +#include <linux/dma-mapping.h>
> > #include <linux/err.h>
> > #include <linux/i2c.h>
> > #include <linux/init.h>
> > @@ -44,6 +47,8 @@
> > #define I2C_FIFO_CONTROL_RX_FLUSH BIT(0)
> > #define I2C_FIFO_CONTROL_TX_TRIG_SHIFT 5
> > #define I2C_FIFO_CONTROL_RX_TRIG_SHIFT 2
> > +#define I2C_FIFO_CONTROL_TX_TRIG(x) (((x) - 1) << 5)
> > +#define I2C_FIFO_CONTROL_RX_TRIG(x) (((x) - 1) << 2)
> > #define I2C_FIFO_STATUS 0x060
> > #define I2C_FIFO_STATUS_TX_MASK 0xF0
> > #define I2C_FIFO_STATUS_TX_SHIFT 4
> > @@ -125,6 +130,19 @@
> > #define I2C_MST_FIFO_STATUS_TX_MASK 0xff0000
> > #define I2C_MST_FIFO_STATUS_TX_SHIFT 16
> >
> > +/* Packet header size in bytes */
> > +#define I2C_PACKET_HEADER_SIZE 12
> > +
> > +#define DATA_DMA_DIR_TX BIT(0)
> > +#define DATA_DMA_DIR_RX BIT(1)
>
> The DATA_DMA_DIR_TX/RX are not used anywhere in the code, let's remove them.
>
> [snip]
>
> TEGRA_I2C_TIMEOUT);
> > tegra_i2c_mask_irq(i2c_dev, int_mask);
> > @@ -814,6 +1133,7 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
> > time_left, completion_done(&i2c_dev->msg_complete),
> > i2c_dev->msg_err);
> >
> > + i2c_dev->is_curr_dma_xfer = false;
>
> This line could be removed because there is no need to clear "is_curr_dma_xfer" at this point.
>
> > if (likely(i2c_dev->msg_err == I2C_ERR_NONE))
> > return 0;
> [snip]
>
>
> 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.

Thierry

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