static void at91_init_twi_bus(struct at91_twi_dev *dev)
{
at91_disable_twi_interrupts(dev);
at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SWRST);
at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_MSEN);
at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SVDIS);
at91_twi_write(dev, AT91_TWI_CWGR, dev->twi_cwgr_reg);
}
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);
if (!irqstatus)
return IRQ_NONE;
else 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;
if (irqstatus & AT91_TWI_TXCOMP) {
at91_disable_twi_interrupts(dev);
complete(&dev->cmd_complete);
}
return IRQ_HANDLED;
}
static void at91_twi_irq_save(struct at91_twi_dev *dev)
{
dev->imr = at91_twi_read(dev, AT91_TWI_IMR) & 0x7;
at91_disable_twi_interrupts(dev);
}
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);
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) {
/*
* Read all available bytes at once by polling RXRDY usable w/
* and w/o FIFO. With FIFO enabled we could also read RXFL and
* avoid polling RXRDY.
*/
do {
at91_twi_read_next_byte(dev);
} while (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY);
}
/*
* 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;
}
