diff options
Diffstat (limited to 'drivers/i2c/busses/i2c-at91.c')
| -rw-r--r-- | drivers/i2c/busses/i2c-at91.c | 82 |
1 files changed, 70 insertions, 12 deletions
diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c index 1c758cd1e..10835d1f5 100644 --- a/drivers/i2c/busses/i2c-at91.c +++ b/drivers/i2c/busses/i2c-at91.c @@ -347,8 +347,14 @@ error: static void at91_twi_read_next_byte(struct at91_twi_dev *dev) { - if (!dev->buf_len) + /* + * 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; + } /* 8bit read works with and without FIFO */ *dev->buf = readb_relaxed(dev->base + AT91_TWI_RHR); @@ -465,19 +471,73 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id) if (!irqstatus) return IRQ_NONE; - else if (irqstatus & AT91_TWI_RXRDY) + /* + * 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); - else if (irqstatus & AT91_TWI_TXRDY) - at91_twi_write_next_byte(dev); - - /* catch error flags */ - dev->transfer_status |= status; + /* + * When a NACK condition is detected, the I2C controller sets the NACK, + * TXCOMP and TXRDY bits all together in the Status Register (SR). + * + * 1 - Handling NACK errors with CPU write transfer. + * + * In such case, we should not write the next byte into the Transmit + * Holding Register (THR) otherwise the I2C controller would start a new + * transfer and the I2C slave is likely to reply by another NACK. + * + * 2 - Handling NACK errors with DMA write transfer. + * + * By setting the TXRDY bit in the SR, the I2C controller also triggers + * the DMA controller to write the next data into the THR. Then the + * result depends on the hardware version of the I2C controller. + * + * 2a - Without support of the Alternative Command mode. + * + * This is the worst case: the DMA controller is triggered to write the + * next data into the THR, hence starting a new transfer: the I2C slave + * is likely to reply by another NACK. + * Concurrently, this interrupt handler is likely to be called to manage + * the first NACK before the I2C controller detects the second NACK and + * sets once again the NACK bit into the SR. + * When handling the first NACK, this interrupt handler disables the I2C + * controller interruptions, especially the NACK interrupt. + * Hence, the NACK bit is pending into the SR. This is why we should + * read the SR to clear all pending interrupts at the beginning of + * at91_do_twi_transfer() before actually starting a new transfer. + * + * 2b - With support of the Alternative Command mode. + * + * When a NACK condition is detected, the I2C controller also locks the + * THR (and sets the LOCK bit in the SR): even though the DMA controller + * is triggered by the TXRDY bit to write the next data into the THR, + * this data actually won't go on the I2C bus hence a second NACK is not + * generated. + */ if (irqstatus & (AT91_TWI_TXCOMP | AT91_TWI_NACK)) { at91_disable_twi_interrupts(dev); complete(&dev->cmd_complete); + } else if (irqstatus & AT91_TWI_TXRDY) { + at91_twi_write_next_byte(dev); } + /* catch error flags */ + dev->transfer_status |= status; + return IRQ_HANDLED; } @@ -537,6 +597,9 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) reinit_completion(&dev->cmd_complete); dev->transfer_status = 0; + /* Clear pending interrupts, such as NACK. */ + at91_twi_read(dev, AT91_TWI_SR); + if (dev->fifo_size) { unsigned fifo_mr = at91_twi_read(dev, AT91_TWI_FMR); @@ -558,11 +621,6 @@ 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 (at91_twi_read(dev, AT91_TWI_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 (!has_alt_cmd && dev->buf_len <= 1 && !(dev->msg->flags & I2C_M_RECV_LEN)) |