Re: [PATCH V8 4/5] i2c: tegra: Update transfer timeout

Thierry Reding
2019-01-31T12:48:13Z

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On Wed, Jan 30, 2019 at 10:16:26PM -0800, Sowjanya Komatineni wrote:
> Tegra194 allows max of 64K bytes and Tegra186 and prior allows
> max of 4K bytes of transfer per packet.
>
> one sec timeout is not enough for transfers more than 10K bytes
> at STD bus rate.
>
> This patch updates I2C transfer timeout based on the transfer size
> and I2C bus rate to allow enough time during max transfer size at
> lower bus speed.
>
> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
> ---
> [V8] : Added comment with explaination of xfer time calculation
> [V5/V6/V7] : Same as V4
> [V4] : V4 series includes bus clear support and this patch is updated with
> fixed timeout of 1sec for bus clear operation.
> [V3] : Same as V2
> [V2] : Added this patch in V2 series to allow enough time for data transfer
> to happen.
> This patch has dependency with DMA patch as TEGRA_I2C_TIMEOUT define
> takes argument with this patch.
>
> drivers/i2c/busses/i2c-tegra.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index 025d63972e50..435518cd91b6 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -25,7 +25,7 @@
> #include <linux/pm_runtime.h>
> #include <linux/reset.h>
>
> -#define TEGRA_I2C_TIMEOUT (msecs_to_jiffies(1000))
> +#define TEGRA_I2C_TIMEOUT(ms) (msecs_to_jiffies(ms))

I think I would've just gone with direct usage of msecs_to_jiffies() but
this is also fine.

> #define BYTES_PER_FIFO_WORD 4
>
> #define I2C_CNFG 0x000
> @@ -901,8 +901,9 @@ static int tegra_i2c_issue_bus_clear(struct tegra_i2c_dev *i2c_dev)
> i2c_writel(i2c_dev, reg, I2C_BUS_CLEAR_CNFG);
> tegra_i2c_unmask_irq(i2c_dev, I2C_INT_BUS_CLR_DONE);
>
> - time_left = wait_for_completion_timeout(&i2c_dev->msg_complete,
> - TEGRA_I2C_TIMEOUT);
> + time_left = wait_for_completion_timeout(
> + &i2c_dev->msg_complete,
> + TEGRA_I2C_TIMEOUT(1000));
> if (time_left == 0) {
> dev_err(i2c_dev->dev, "timed out for bus clear\n");
> return -ETIMEDOUT;
> @@ -930,6 +931,7 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
> int err = 0;
> bool dma = false;
> struct dma_chan *chan;
> + u16 xfer_time = 100;
>
> tegra_i2c_flush_fifos(i2c_dev);
>
> @@ -945,6 +947,13 @@ 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);
> + /*
> + * Transfer time = Total bits / transfer rate
> + * Total bits = 9 bits per byte (including ACK bit) + Start & stop bits
> + */
> + xfer_time += DIV_ROUND_CLOSEST(((xfer_size * 9) + 2) * 1000,

This doesn't really explain the factor of 1000 in there, which I assume
is just to scale this to milliseconds required by msecs_to_jiffies().
Might be worth to replace it by MSEC_PER_SEC to clarify the purpose.

With that fixed:

Acked-by: Thierry Reding <treding@nvidia.com>

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