diff options
Diffstat (limited to 'drivers/i2c/busses/i2c-at91.c')
| -rw-r--r-- | drivers/i2c/busses/i2c-at91.c | 70 |
1 files changed, 53 insertions, 17 deletions
diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c index 8873d84e1d4f..50862c948217 100644 --- a/drivers/i2c/busses/i2c-at91.c +++ b/drivers/i2c/busses/i2c-at91.c @@ -62,6 +62,9 @@ #define AT91_TWI_UNRE 0x0080 /* Underrun Error */ #define AT91_TWI_NACK 0x0100 /* Not Acknowledged */ +#define AT91_TWI_INT_MASK \ + (AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY | AT91_TWI_NACK) + #define AT91_TWI_IER 0x0024 /* Interrupt Enable Register */ #define AT91_TWI_IDR 0x0028 /* Interrupt Disable Register */ #define AT91_TWI_IMR 0x002c /* Interrupt Mask Register */ @@ -117,13 +120,12 @@ static void at91_twi_write(struct at91_twi_dev *dev, unsigned reg, unsigned val) static void at91_disable_twi_interrupts(struct at91_twi_dev *dev) { - at91_twi_write(dev, AT91_TWI_IDR, - AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY); + at91_twi_write(dev, AT91_TWI_IDR, AT91_TWI_INT_MASK); } static void at91_twi_irq_save(struct at91_twi_dev *dev) { - dev->imr = at91_twi_read(dev, AT91_TWI_IMR) & 0x7; + dev->imr = at91_twi_read(dev, AT91_TWI_IMR) & AT91_TWI_INT_MASK; at91_disable_twi_interrupts(dev); } @@ -213,6 +215,14 @@ static void at91_twi_write_data_dma_callback(void *data) dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg), dev->buf_len, DMA_TO_DEVICE); + /* + * When this callback is called, THR/TX FIFO is likely not to be empty + * yet. So we have to wait for TXCOMP or NACK bits to be set into the + * Status Register to be sure that the STOP bit has been sent and the + * transfer is completed. The NACK interrupt has already been enabled, + * we just have to enable TXCOMP one. + */ + at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP); at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP); } @@ -307,7 +317,7 @@ static void at91_twi_read_data_dma_callback(void *data) /* The last two bytes have to be read without using dma */ dev->buf += dev->buf_len - 2; dev->buf_len = 2; - at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_RXRDY); + at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_RXRDY | AT91_TWI_TXCOMP); } static void at91_twi_read_data_dma(struct at91_twi_dev *dev) @@ -368,7 +378,7 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id) /* catch error flags */ dev->transfer_status |= status; - if (irqstatus & AT91_TWI_TXCOMP) { + if (irqstatus & (AT91_TWI_TXCOMP | AT91_TWI_NACK)) { at91_disable_twi_interrupts(dev); complete(&dev->cmd_complete); } @@ -381,6 +391,34 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) int ret; bool has_unre_flag = dev->pdata->has_unre_flag; + /* + * WARNING: the TXCOMP bit in the Status Register is NOT a clear on + * read flag but shows the state of the transmission at the time the + * Status Register is read. According to the programmer datasheet, + * TXCOMP is set when both holding register and internal shifter are + * empty and STOP condition has been sent. + * Consequently, we should enable NACK interrupt rather than TXCOMP to + * detect transmission failure. + * + * Besides, the TXCOMP bit is already set before the i2c transaction + * has been started. For read transactions, this bit is cleared when + * writing the START bit into the Control Register. So the + * corresponding interrupt can safely be enabled just after. + * However for write transactions managed by the CPU, we first write + * into THR, so TXCOMP is cleared. Then we can safely enable TXCOMP + * interrupt. If TXCOMP interrupt were enabled before writing into THR, + * the interrupt handler would be called immediately and the i2c command + * would be reported as completed. + * Also when a write transaction is managed by the DMA controller, + * enabling the TXCOMP interrupt in this function may lead to a race + * condition since we don't know whether the TXCOMP interrupt is enabled + * before or after the DMA has started to write into THR. So the TXCOMP + * interrupt is enabled later by at91_twi_write_data_dma_callback(). + * Immediately after in that DMA callback, we still need to send the + * STOP condition manually writing the corresponding bit into the + * Control Register. + */ + dev_dbg(dev->dev, "transfer: %s %d bytes.\n", (dev->msg->flags & I2C_M_RD) ? "read" : "write", dev->buf_len); @@ -411,26 +449,24 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) * seems to be the best solution. */ if (dev->use_dma && (dev->buf_len > AT91_I2C_DMA_THRESHOLD)) { + at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_NACK); at91_twi_read_data_dma(dev); - /* - * It is important to enable TXCOMP irq here because - * doing it only when transferring the last two bytes - * will mask NACK errors since TXCOMP is set when a - * NACK occurs. - */ - at91_twi_write(dev, AT91_TWI_IER, - AT91_TWI_TXCOMP); - } else + } else { at91_twi_write(dev, AT91_TWI_IER, - AT91_TWI_TXCOMP | AT91_TWI_RXRDY); + AT91_TWI_TXCOMP | + AT91_TWI_NACK | + AT91_TWI_RXRDY); + } } else { if (dev->use_dma && (dev->buf_len > AT91_I2C_DMA_THRESHOLD)) { + at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_NACK); at91_twi_write_data_dma(dev); - at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP); } else { at91_twi_write_next_byte(dev); at91_twi_write(dev, AT91_TWI_IER, - AT91_TWI_TXCOMP | AT91_TWI_TXRDY); + AT91_TWI_TXCOMP | + AT91_TWI_NACK | + AT91_TWI_TXRDY); } } |