linux-kernel - Re: [PATCH] i2c-at91: fix data-loss issue

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Date:	Sat, 14 Apr 2012 08:06:13 +1000
From:	Ryan Mallon <rmallon@...il.com>
To:	Hubert Feurstein <h.feurstein@...il.com>
CC:	Nikolaus Voss <n.voss@...nmann.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org, nicolas.ferre@...el.com,
	ben-linux@...ff.org, balbi@...com
Subject: Re: [PATCH] i2c-at91: fix data-loss issue

On 13/04/12 21:44, Hubert Feurstein wrote:

> In the interrupt handler both status-flags (TXCOMP and RXRDY) might be
> pending at the same time. In this case TXCOMP is handled but NOT RXRDY
> which causes a data-loss on the current transfer. As a consequence also the
> next transfer will be corrupt, because old data is pending in RHR.
> 
> To make sure that we do not start with old data in any case, SR and RHR is
> read empty before initiating a new transfer.
> 
> Signed-off-by: Hubert Feurstein <h.feurstein@...il.com>


Couple of very minor comments below.

~Ryan

> ---
>  This patch applies on top of [PATCH v9 3/4] drivers/i2c/busses/i2c-at91.c: add new driver
> 
>  drivers/i2c/busses/i2c-at91.c |   23 ++++++++++++++++-------
>  1 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> index 40c39a2..295835f 100644
> --- a/drivers/i2c/busses/i2c-at91.c
> +++ b/drivers/i2c/busses/i2c-at91.c
> @@ -161,18 +161,22 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
>  {
>  	struct at91_twi_dev *dev = dev_id;
>  	const unsigned status = at91_twi_read(dev, AT91_TWI_SR);
> -	const unsigned irqstatus = status & at91_twi_read(dev, AT91_TWI_IMR);
> +	unsigned irqstatus = status & at91_twi_read(dev, AT91_TWI_IMR);
> +
> +	irqstatus &= (AT91_TWI_RXRDY | AT91_TWI_TXRDY | AT91_TWI_TXCOMP);

> +	if (!irqstatus)
> +		return IRQ_NONE;
> +
> +	if (irqstatus & AT91_TWI_RXRDY)
> +		at91_twi_read_next_byte(dev);
> +
> +	if (irqstatus & AT91_TWI_TXRDY)
> +		at91_twi_write_next_byte(dev);
>  
>  	if (irqstatus & AT91_TWI_TXCOMP) {
>  		at91_disable_twi_interrupts(dev);
>  		dev->transfer_status = status;
>  		complete(&dev->cmd_complete);
> -	} else if (irqstatus & AT91_TWI_RXRDY) {
> -		at91_twi_read_next_byte(dev);
> -	} else if (irqstatus & AT91_TWI_TXRDY) {
> -		at91_twi_write_next_byte(dev);
> -	} else {
> -		return IRQ_NONE;
>  	}
>  
>  	return IRQ_HANDLED;
> @@ -189,6 +193,10 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
>  	if (dev->msg->flags & I2C_M_RD) {
>  		unsigned start_flags = AT91_TWI_START;
>  
> +		/* clear any pending data */
> +		(void)at91_twi_read(dev, AT91_TWI_SR);
> +		(void)at91_twi_read(dev, AT91_TWI_RHR);


Drop the void cast.

> +
>  		/* if only one byte is to be read, immediately stop transfer */
>  		if (dev->buf_len <= 1 && !(dev->msg->flags & I2C_M_RECV_LEN))
>  			start_flags |= AT91_TWI_STOP;
> @@ -259,6 +267,7 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
>  			internal_address |= addr << (8 * i);
>  			int_addr_flag += AT91_TWI_IADRSZ_1;
>  		}
> +


Please don't make unrelated whitespace changes.

>  		at91_twi_write(dev, AT91_TWI_IADR, internal_address);
>  	}
>  


With those fixed, please add:

Reviewed-by: Ryan Mallon <rmallon@...il.com>
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