linux-kernel - Re: [PATCH 06/12] i2c: qup: proper error handling for i2c error in BAM mode

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Date:   Tue, 27 Feb 2018 15:00:06 -0700
From:   "Christ, Austin" <austinwc@...eaurora.org>
To:     Abhishek Sahu <absahu@...eaurora.org>,
        Andy Gross <andy.gross@...aro.org>,
        Wolfram Sang <wsa@...-dreams.de>
Cc:     David Brown <david.brown@...aro.org>,
        Sricharan R <sricharan@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/12] i2c: qup: proper error handling for i2c error in
 BAM mode

Tested on Centriq 2400

Reviewed-by: Austin Christ <austinwc@...eaurora.org>

On 2/3/2018 12:58 AM, Abhishek Sahu wrote:
> Currently the i2c error handling in BAM mode is not working
> properly in stress condition.
> 
> 1. After an error, the FIFO are being written with FLUSH and
>     EOT tags which should not be required since already these tags
>     have been written in BAM descriptor itself.
> 
> 2. QUP state is being moved to RESET in IRQ handler in case
>     of error. When QUP HW encounters an error in BAM mode then it
>     moves the QUP STATE to PAUSE state. In this case, I2C_FLUSH
>     command needs to be executed while moving to RUN_STATE by writing
>     to the QUP_STATE register with the I2C_FLUSH bit set to 1.
> 
> 3. In Error case, sometimes, QUP generates more than one
>     interrupt which will trigger the complete again. After an error,
>     the flush operation will be scheduled after doing
>     reinit_completion which should be triggered by BAM IRQ callback.
>     If the second QUP IRQ comes during this time then it will call
>     the complete and the transfer function will assume the all the
>     BAM HW descriptors have been completed.
> 
> 4. The release DMA is being called after each error which
>     will free the DMA tx and rx channels. The error like NACK is very
>     common in I2C transfer and every time this will be overhead. Now,
>     since the error handling is proper so this release channel can be
>     completely avoided.
> 
> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
> ---
>   drivers/i2c/busses/i2c-qup.c | 25 ++++++++++++++++---------
>   1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
> index 094be6a..6227a5c 100644
> --- a/drivers/i2c/busses/i2c-qup.c
> +++ b/drivers/i2c/busses/i2c-qup.c
> @@ -228,9 +228,24 @@ static irqreturn_t qup_i2c_interrupt(int irq, void *dev)
>   	if (bus_err)
>   		writel(bus_err, qup->base + QUP_I2C_STATUS);
>   
> +	/*
> +	 * Check for BAM mode and returns if already error has come for current
> +	 * transfer. In Error case, sometimes, QUP generates more than one
> +	 * interrupt.
> +	 */
> +	if (qup->use_dma && (qup->qup_err || qup->bus_err))
> +		return IRQ_HANDLED;
> +
>   	/* Reset the QUP State in case of error */
>   	if (qup_err || bus_err) {
> -		writel(QUP_RESET_STATE, qup->base + QUP_STATE);
> +		/*
> +		 * Don’t reset the QUP state in case of BAM mode. The BAM
> +		 * flush operation needs to be scheduled in transfer function
> +		 * which will clear the remaining schedule descriptors in BAM
> +		 * HW FIFO and generates the BAM interrupt.
> +		 */
> +		if (!qup->use_dma)
> +			writel(QUP_RESET_STATE, qup->base + QUP_STATE);
>   		goto done;
>   	}
>   
> @@ -841,20 +856,12 @@ static int qup_i2c_bam_do_xfer(struct qup_i2c_dev *qup, struct i2c_msg *msg,
>   			goto desc_err;
>   		}
>   
> -		if (rx_buf)
> -			writel(QUP_BAM_INPUT_EOT,
> -			       qup->base + QUP_OUT_FIFO_BASE);
> -
> -		writel(QUP_BAM_FLUSH_STOP, qup->base + QUP_OUT_FIFO_BASE);
> -
>   		qup_i2c_flush(qup);
>   
>   		/* wait for remaining interrupts to occur */
>   		if (!wait_for_completion_timeout(&qup->xfer, HZ))
>   			dev_err(qup->dev, "flush timed out\n");
>   
> -		qup_i2c_rel_dma(qup);
> -
>   		ret =  (qup->bus_err & QUP_I2C_NACK_FLAG) ? -ENXIO : -EIO;
>   	}
>   
> 

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