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author | Nandor Han <nandor.han@ge.com> | 2016-08-08 15:38:27 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-08-31 16:27:28 +0200 |
commit | 9d297239b8cbf276b1b3bc6cbde5c0dd9ca79a61 (patch) | |
tree | fe49bf94240b6648b02aad654fd1cbff3099dd7d | |
parent | 5881826ded79cf3c3314ee2d84c3bfa94e111b42 (diff) | |
download | op-kernel-dev-9d297239b8cbf276b1b3bc6cbde5c0dd9ca79a61.zip op-kernel-dev-9d297239b8cbf276b1b3bc6cbde5c0dd9ca79a61.tar.gz |
serial: imx-serial - update UART IMX driver to use cyclic DMA
The IMX UART has a 32 bytes HW buffer which can be filled up in
2777us at 115200 baud or 80us at 4Mbaud (supported by IMX53).
Taking this in consideration there is a good probability to lose
data because of the DMA startup latency.
Our tests (explained below) indicates a latency up to 4400us when
creating interrupt load and ~70us without. When creating interrupt
load I was able to see continuous overrun errors by checking serial
driver statistics using the command:
`cat /proc/tty/driver/IMX-uart`.
Replace manual restart of DMA with cyclic DMA to eliminate data loss
due to DMA engine startup latency (similar approch to atmel_serial.c
driver). As result the DMA engine will start on the first serial data
transfer and stops only when serial port is closed.
Tests environment:
Using the m53evk board I have used a GPIO for profiling the IMX
serial driver.
- The RX line and GPIO were connected to oscilloscope.
- Run a small test program on the m53evk board that will only open
and read data from ttymxc2 port.
- Connect the ttymxc2 port to my laptop using a USB serial converter
where another test program is running, able to send configurable
packet lengths and intervals.
- Serial ports configured at 115200 8N1.
- Interrupts load created by disconnecting/connecting (3s interval)
a USB hub, using a digital switch, with 4 USB devices (USB-Serial
converter, USB SD card, etc) connected.
(around 160 interrupts/second generated)
- The GPIO was toggled HI in the `imx_int` when USR1_RRDY or USR1_AGTIM
events are received and toggled back, once the DMA configuration
is finalized, at the end of `imx_dma_rxint`.
Measurements:
The measurements were done from the end of the last byte (RX line) until
the GPIO was toggled back LOW.
Note: The GPIO toggling was done using `gpiod_set_value` method.
Tests performed:
1. Sending 9 bytes packets at 8ms interval. Having the 9 bytes packets
will activate the RRDY threshold event and IMX serial interrupt
called.
Results:
- DMA start latency (interrupt start latency +
DMA configuration) consistently 70us when system not loaded.
- DMA start latency up to 4400us when system loaded.
2. Sending 40 bytes packet at 8mS interval.
Results with load:
- Able to observe overruns by running:
`watch -n1 cat /proc/tty/driver/IMX-uart`
Tested-by: Peter Senna Tschudin <peter.senna@collabora.com>
Acked-by: Peter Senna Tschudin <peter.senna@collabora.com>
Signed-off-by: Nandor Han <nandor.han@ge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | drivers/tty/serial/imx.c | 141 |
1 files changed, 78 insertions, 63 deletions
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 0df2b1c..1912136 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -222,6 +222,9 @@ struct imx_port { struct dma_chan *dma_chan_rx, *dma_chan_tx; struct scatterlist rx_sgl, tx_sgl[2]; void *rx_buf; + struct circ_buf rx_ring; + unsigned int rx_periods; + dma_cookie_t rx_cookie; unsigned int tx_bytes; unsigned int dma_tx_nents; wait_queue_head_t dma_wait; @@ -932,30 +935,6 @@ static void imx_timeout(unsigned long data) } #define RX_BUF_SIZE (PAGE_SIZE) -static void imx_rx_dma_done(struct imx_port *sport) -{ - unsigned long temp; - unsigned long flags; - - spin_lock_irqsave(&sport->port.lock, flags); - - /* re-enable interrupts to get notified when new symbols are incoming */ - temp = readl(sport->port.membase + UCR1); - temp |= UCR1_RRDYEN; - writel(temp, sport->port.membase + UCR1); - - temp = readl(sport->port.membase + UCR2); - temp |= UCR2_ATEN; - writel(temp, sport->port.membase + UCR2); - - sport->dma_is_rxing = 0; - - /* Is the shutdown waiting for us? */ - if (waitqueue_active(&sport->dma_wait)) - wake_up(&sport->dma_wait); - - spin_unlock_irqrestore(&sport->port.lock, flags); -} /* * There are two kinds of RX DMA interrupts(such as in the MX6Q): @@ -972,43 +951,75 @@ static void dma_rx_callback(void *data) struct scatterlist *sgl = &sport->rx_sgl; struct tty_port *port = &sport->port.state->port; struct dma_tx_state state; + struct circ_buf *rx_ring = &sport->rx_ring; enum dma_status status; - unsigned int count; - - /* unmap it first */ - dma_unmap_sg(sport->port.dev, sgl, 1, DMA_FROM_DEVICE); + unsigned int w_bytes = 0; + unsigned int r_bytes; + unsigned int bd_size; status = dmaengine_tx_status(chan, (dma_cookie_t)0, &state); - count = RX_BUF_SIZE - state.residue; - dev_dbg(sport->port.dev, "We get %d bytes.\n", count); + if (status == DMA_ERROR) { + dev_err(sport->port.dev, "DMA transaction error.\n"); + return; + } + + if (!(sport->port.ignore_status_mask & URXD_DUMMY_READ)) { + + /* + * The state-residue variable represents the empty space + * relative to the entire buffer. Taking this in consideration + * the head is always calculated base on the buffer total + * length - DMA transaction residue. The UART script from the + * SDMA firmware will jump to the next buffer descriptor, + * once a DMA transaction if finalized (IMX53 RM - A.4.1.2.4). + * Taking this in consideration the tail is always at the + * beginning of the buffer descriptor that contains the head. + */ + + /* Calculate the head */ + rx_ring->head = sg_dma_len(sgl) - state.residue; + + /* Calculate the tail. */ + bd_size = sg_dma_len(sgl) / sport->rx_periods; + rx_ring->tail = ((rx_ring->head-1) / bd_size) * bd_size; + + if (rx_ring->head <= sg_dma_len(sgl) && + rx_ring->head > rx_ring->tail) { + + /* Move data from tail to head */ + r_bytes = rx_ring->head - rx_ring->tail; + + /* CPU claims ownership of RX DMA buffer */ + dma_sync_sg_for_cpu(sport->port.dev, sgl, 1, + DMA_FROM_DEVICE); - if (count) { - if (!(sport->port.ignore_status_mask & URXD_DUMMY_READ)) { - int bytes = tty_insert_flip_string(port, sport->rx_buf, - count); + w_bytes = tty_insert_flip_string(port, + sport->rx_buf + rx_ring->tail, r_bytes); - if (bytes != count) + /* UART retrieves ownership of RX DMA buffer */ + dma_sync_sg_for_device(sport->port.dev, sgl, 1, + DMA_FROM_DEVICE); + + if (w_bytes != r_bytes) sport->port.icount.buf_overrun++; + + sport->port.icount.rx += w_bytes; + } else { + WARN_ON(rx_ring->head > sg_dma_len(sgl)); + WARN_ON(rx_ring->head <= rx_ring->tail); } - tty_flip_buffer_push(port); - sport->port.icount.rx += count; } - /* - * Restart RX DMA directly if more data is available in order to skip - * the roundtrip through the IRQ handler. If there is some data already - * in the FIFO, DMA needs to be restarted soon anyways. - * - * Otherwise stop the DMA and reactivate FIFO IRQs to restart DMA once - * data starts to arrive again. - */ - if (readl(sport->port.membase + USR2) & USR2_RDR) - start_rx_dma(sport); - else - imx_rx_dma_done(sport); + if (w_bytes) { + tty_flip_buffer_push(port); + dev_dbg(sport->port.dev, "We get %d bytes.\n", w_bytes); + } } +/* RX DMA buffer periods */ +#define RX_DMA_PERIODS 4 + static int start_rx_dma(struct imx_port *sport) { struct scatterlist *sgl = &sport->rx_sgl; @@ -1017,14 +1028,21 @@ static int start_rx_dma(struct imx_port *sport) struct dma_async_tx_descriptor *desc; int ret; + sport->rx_ring.head = 0; + sport->rx_ring.tail = 0; + sport->rx_periods = RX_DMA_PERIODS; + sg_init_one(sgl, sport->rx_buf, RX_BUF_SIZE); ret = dma_map_sg(dev, sgl, 1, DMA_FROM_DEVICE); if (ret == 0) { dev_err(dev, "DMA mapping error for RX.\n"); return -EINVAL; } - desc = dmaengine_prep_slave_sg(chan, sgl, 1, DMA_DEV_TO_MEM, - DMA_PREP_INTERRUPT); + + desc = dmaengine_prep_dma_cyclic(chan, sg_dma_address(sgl), + sg_dma_len(sgl), sg_dma_len(sgl) / sport->rx_periods, + DMA_DEV_TO_MEM, DMA_PREP_INTERRUPT); + if (!desc) { dma_unmap_sg(dev, sgl, 1, DMA_FROM_DEVICE); dev_err(dev, "We cannot prepare for the RX slave dma!\n"); @@ -1034,7 +1052,7 @@ static int start_rx_dma(struct imx_port *sport) desc->callback_param = sport; dev_dbg(dev, "RX: prepare for the DMA.\n"); - dmaengine_submit(desc); + sport->rx_cookie = dmaengine_submit(desc); dma_async_issue_pending(chan); return 0; } @@ -1058,14 +1076,16 @@ static void imx_setup_ufcr(struct imx_port *sport, static void imx_uart_dma_exit(struct imx_port *sport) { if (sport->dma_chan_rx) { + dmaengine_terminate_all(sport->dma_chan_rx); dma_release_channel(sport->dma_chan_rx); sport->dma_chan_rx = NULL; - + sport->rx_cookie = -EINVAL; kfree(sport->rx_buf); sport->rx_buf = NULL; } if (sport->dma_chan_tx) { + dmaengine_terminate_all(sport->dma_chan_tx); dma_release_channel(sport->dma_chan_tx); sport->dma_chan_tx = NULL; } @@ -1103,6 +1123,7 @@ static int imx_uart_dma_init(struct imx_port *sport) ret = -ENOMEM; goto err; } + sport->rx_ring.buf = sport->rx_buf; /* Prepare for TX : */ sport->dma_chan_tx = dma_request_slave_channel(dev, "tx"); @@ -1283,17 +1304,11 @@ static void imx_shutdown(struct uart_port *port) unsigned long flags; if (sport->dma_is_enabled) { - int ret; + sport->dma_is_rxing = 0; + sport->dma_is_txing = 0; + dmaengine_terminate_all(sport->dma_chan_tx); + dmaengine_terminate_all(sport->dma_chan_rx); - /* We have to wait for the DMA to finish. */ - ret = wait_event_interruptible(sport->dma_wait, - !sport->dma_is_rxing && !sport->dma_is_txing); - if (ret != 0) { - sport->dma_is_rxing = 0; - sport->dma_is_txing = 0; - dmaengine_terminate_all(sport->dma_chan_tx); - dmaengine_terminate_all(sport->dma_chan_rx); - } spin_lock_irqsave(&sport->port.lock, flags); imx_stop_tx(port); imx_stop_rx(port); |