linux-kernel - Re: [PATCH V3 2/3] i2c: tegra: Update transfer timeout

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Date:   Sat, 26 Jan 2019 21:02:05 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com,
        mkarthik@...dia.com, smohammed@...dia.com, talho@...dia.com
Cc:     linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org
Subject: Re: [PATCH V3 2/3] i2c: tegra: Update transfer timeout

26.01.2019 6:57, Sowjanya Komatineni пишет:
> Update I2C transfer timeout based on transfer bytes and I2C bus
> rate to allow enough time during max transfer size based on the
> speed.

Could it be that I2C device is busy and just slowly handling the transfer requests? Maybe better to leave the timeout as-is and assume the worst case scenario?

> 
> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
> ---
>  [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 | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index aec500ef9a98..3dcbc9960d9d 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -23,7 +23,7 @@
>  #include <linux/reset.h>
>  #include <linux/slab.h>
>  
> -#define TEGRA_I2C_TIMEOUT (msecs_to_jiffies(1000))
> +#define TEGRA_I2C_TIMEOUT(ms) (msecs_to_jiffies(ms))
>  #define BYTES_PER_FIFO_WORD 4
>  
>  #define I2C_CNFG				0x000
> @@ -116,6 +116,9 @@
>  #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
> +
>  /*
>   * msg_end_type: The bus control which need to be send at end of transfer.
>   * @MSG_END_STOP: Send stop pulse at end of transfer.
> @@ -683,6 +686,17 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
>  	u32 int_mask;
>  	unsigned long time_left;
>  	unsigned long flags;
> +	u16 xfer_time = 100;
> +	size_t xfer_size = 0;

No need to initialize xfer_size to 0.

> +
> +	if (msg->flags & I2C_M_RD)
> +		xfer_size = ALIGN(msg->len, BYTES_PER_FIFO_WORD);
> +	else
> +		xfer_size = ALIGN(msg->len, BYTES_PER_FIFO_WORD) +
> +			    I2C_PACKET_HEADER_SIZE;
> +
> +	xfer_time += DIV_ROUND_CLOSEST((xfer_size * 9) * 1000,
> +					i2c_dev->bus_clk_rate);>  
>  	tegra_i2c_flush_fifos(i2c_dev);
>  
> @@ -739,7 +753,7 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
>  		i2c_readl(i2c_dev, I2C_INT_MASK));
>  
>  	time_left = wait_for_completion_timeout(&i2c_dev->msg_complete,
> -						TEGRA_I2C_TIMEOUT);
> +						TEGRA_I2C_TIMEOUT(xfer_time));
>  	tegra_i2c_mask_irq(i2c_dev, int_mask);
>  
>  	if (time_left == 0) {
>