#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 */
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);
}
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);
}
/* 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)
/* 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);
}
unsigned long time_left;
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);
* 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);
}
}
Code Review / kvmfornfv.git / blobdiff