diff options
| -rw-r--r-- | drivers/tty/serial/atmel_serial.c | 94 |
1 files changed, 55 insertions, 39 deletions
diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c index 8a84034d130c..9eb624a22431 100644 --- a/drivers/tty/serial/atmel_serial.c +++ b/drivers/tty/serial/atmel_serial.c @@ -880,32 +880,6 @@ chan_err: return -EINVAL; } -static void atmel_flip_buffer_rx_dma(struct uart_port *port, - char *buf, size_t count) -{ - struct atmel_uart_port *atmel_port = to_atmel_uart_port(port); - struct tty_port *tport = &port->state->port; - - dma_sync_sg_for_cpu(port->dev, - &atmel_port->sg_rx, - 1, - DMA_DEV_TO_MEM); - - tty_insert_flip_string(tport, buf, count); - - dma_sync_sg_for_device(port->dev, - &atmel_port->sg_rx, - 1, - DMA_DEV_TO_MEM); - /* - * Drop the lock here since it might end up calling - * uart_start(), which takes the lock. - */ - spin_unlock(&port->lock); - tty_flip_buffer_push(tport); - spin_lock(&port->lock); -} - static void atmel_complete_rx_dma(void *arg) { struct uart_port *port = arg; @@ -934,11 +908,12 @@ static void atmel_release_rx_dma(struct uart_port *port) static void atmel_rx_from_dma(struct uart_port *port) { struct atmel_uart_port *atmel_port = to_atmel_uart_port(port); + struct tty_port *tport = &port->state->port; struct circ_buf *ring = &atmel_port->rx_ring; struct dma_chan *chan = atmel_port->chan_rx; struct dma_tx_state state; enum dma_status dmastat; - size_t pending, count; + size_t count; /* Reset the UART timeout early so that we don't miss one */ @@ -953,27 +928,68 @@ static void atmel_rx_from_dma(struct uart_port *port) tasklet_schedule(&atmel_port->tasklet); return; } - /* current transfer size should no larger than dma buffer */ - pending = sg_dma_len(&atmel_port->sg_rx) - state.residue; - BUG_ON(pending > sg_dma_len(&atmel_port->sg_rx)); + /* CPU claims ownership of RX DMA buffer */ + dma_sync_sg_for_cpu(port->dev, + &atmel_port->sg_rx, + 1, + DMA_DEV_TO_MEM); + + /* + * ring->head points to the end of data already written by the DMA. + * ring->tail points to the beginning of data to be read by the + * framework. + * The current transfer size should not be larger than the dma buffer + * length. + */ + ring->head = sg_dma_len(&atmel_port->sg_rx) - state.residue; + BUG_ON(ring->head > sg_dma_len(&atmel_port->sg_rx)); /* - * This will take the chars we have so far, - * ring->head will record the transfer size, only new bytes come - * will insert into the framework. + * At this point ring->head may point to the first byte right after the + * last byte of the dma buffer: + * 0 <= ring->head <= sg_dma_len(&atmel_port->sg_rx) + * + * However ring->tail must always points inside the dma buffer: + * 0 <= ring->tail <= sg_dma_len(&atmel_port->sg_rx) - 1 + * + * Since we use a ring buffer, we have to handle the case + * where head is lower than tail. In such a case, we first read from + * tail to the end of the buffer then reset tail. */ - if (pending > ring->head) { - count = pending - ring->head; + if (ring->head < ring->tail) { + count = sg_dma_len(&atmel_port->sg_rx) - ring->tail; - atmel_flip_buffer_rx_dma(port, ring->buf + ring->head, count); + tty_insert_flip_string(tport, ring->buf + ring->tail, count); + ring->tail = 0; + port->icount.rx += count; + } - ring->head += count; - if (ring->head == sg_dma_len(&atmel_port->sg_rx)) - ring->head = 0; + /* Finally we read data from tail to head */ + if (ring->tail < ring->head) { + count = ring->head - ring->tail; + tty_insert_flip_string(tport, ring->buf + ring->tail, count); + /* Wrap ring->head if needed */ + if (ring->head >= sg_dma_len(&atmel_port->sg_rx)) + ring->head = 0; + ring->tail = ring->head; port->icount.rx += count; } + /* USART retreives ownership of RX DMA buffer */ + dma_sync_sg_for_device(port->dev, + &atmel_port->sg_rx, + 1, + DMA_DEV_TO_MEM); + + /* + * Drop the lock here since it might end up calling + * uart_start(), which takes the lock. + */ + spin_unlock(&port->lock); + tty_flip_buffer_push(tport); + spin_lock(&port->lock); + UART_PUT_IER(port, ATMEL_US_TIMEOUT); } |