From: Ludovic Desroches <[email protected]> 3.12-stable review patch. If anyone has any objections, please let me know.
=============== commit a9bed6b10bd117a300cceb9062003f7a2761ef99 upstream. In some cases, we could start a new i2c transfer with the RXRDY flag set. It is not a clean state and it leads to print annoying error messages even if there no real issue. The cause is only having garbage data in the Receive Holding Register because of a weird behavior of the RXRDY flag. Reported-by: Peter Rosin <[email protected]> Signed-off-by: Ludovic Desroches <[email protected]> Tested-by: Peter Rosin <[email protected]> Signed-off-by: Wolfram Sang <[email protected]> Fixes: 93563a6a71bb ("i2c: at91: fix a race condition when using the DMA controller") Signed-off-by: Jiri Slaby <[email protected]> --- drivers/i2c/busses/i2c-at91.c | 36 ++++++++++++++++++++++++++---------- 1 file changed, 26 insertions(+), 10 deletions(-) diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c index e6f18b241255..70782d560407 100644 --- a/drivers/i2c/busses/i2c-at91.c +++ b/drivers/i2c/busses/i2c-at91.c @@ -272,8 +272,14 @@ error: static void at91_twi_read_next_byte(struct at91_twi_dev *dev) { - if (dev->buf_len <= 0) + /* + * If we are in this case, it means there is garbage data in RHR, so + * delete them. + */ + if (!dev->buf_len) { + at91_twi_read(dev, AT91_TWI_RHR); return; + } *dev->buf = at91_twi_read(dev, AT91_TWI_RHR) & 0xff; --dev->buf_len; @@ -370,6 +376,24 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id) if (!irqstatus) return IRQ_NONE; + /* + * In reception, the behavior of the twi device (before sama5d2) is + * weird. There is some magic about RXRDY flag! When a data has been + * almost received, the reception of a new one is anticipated if there + * is no stop command to send. That is the reason why ask for sending + * the stop command not on the last data but on the second last one. + * + * Unfortunately, we could still have the RXRDY flag set even if the + * transfer is done and we have read the last data. It might happen + * when the i2c slave device sends too quickly data after receiving the + * ack from the master. The data has been almost received before having + * the order to send stop. In this case, sending the stop command could + * cause a RXRDY interrupt with a TXCOMP one. It is better to manage + * the RXRDY interrupt first in order to not keep garbage data in the + * Receive Holding Register for the next transfer. + */ + if (irqstatus & AT91_TWI_RXRDY) + at91_twi_read_next_byte(dev); /* * When a NACK condition is detected, the I2C controller sets the NACK, @@ -412,8 +436,6 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id) if (irqstatus & (AT91_TWI_TXCOMP | AT91_TWI_NACK)) { at91_disable_twi_interrupts(dev); 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); } @@ -428,7 +450,6 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) { int ret; bool has_unre_flag = dev->pdata->has_unre_flag; - unsigned sr; /* * WARNING: the TXCOMP bit in the Status Register is NOT a clear on @@ -465,7 +486,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) dev->transfer_status = 0; /* Clear pending interrupts, such as NACK. */ - sr = at91_twi_read(dev, AT91_TWI_SR); + at91_twi_read(dev, AT91_TWI_SR); if (!dev->buf_len) { at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_QUICK); @@ -473,11 +494,6 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) } else if (dev->msg->flags & I2C_M_RD) { unsigned start_flags = AT91_TWI_START; - if (sr & AT91_TWI_RXRDY) { - dev_err(dev->dev, "RXRDY still set!"); - at91_twi_read(dev, AT91_TWI_RHR); - } - /* 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; -- 2.12.2
