serial: imx: optimization: remove the workqueues for DMA

I worried that the delay of the sdma_run_channel0() maybe too long for
interrupt context, so I added the workqueues for RX/TX DMA.

But tested with bluetooth device, I find that the delay of sdma_run_channel0()
is about 8us (tested in imx6dl sabreauto board). I think the delay
is acceptable.

This patch removes the RX/TX workqueues for DMA, it makes the
code more clear.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 13c2c2d09cacaef2b6ec36c6acff3ac7a1839dfa..bb84f8d4c54e3a6d1e810692c85065bd060434fa 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -223,8 +223,7 @@ struct imx_port {
        struct dma_chan         *dma_chan_rx, *dma_chan_tx;
        struct scatterlist      rx_sgl, tx_sgl[2];
        void                    *rx_buf;
-       unsigned int            rx_bytes, tx_bytes;
-       struct work_struct      tsk_dma_rx, tsk_dma_tx;
+       unsigned int            tx_bytes;
        unsigned int            dma_tx_nents;
        wait_queue_head_t       dma_wait;
 };
@@ -505,32 +504,23 @@ static void dma_tx_callback(void *data)
                dev_dbg(sport->port.dev, "exit in %s.\n", __func__);
                return;
        }
-
-       schedule_work(&sport->tsk_dma_tx);
 }
 
-static void dma_tx_work(struct work_struct *w)
+static void imx_dma_tx(struct imx_port *sport)
 {
-       struct imx_port *sport = container_of(w, struct imx_port, tsk_dma_tx);
        struct circ_buf *xmit = &sport->port.state->xmit;
        struct scatterlist *sgl = sport->tx_sgl;
        struct dma_async_tx_descriptor *desc;
        struct dma_chan *chan = sport->dma_chan_tx;
        struct device *dev = sport->port.dev;
        enum dma_status status;
-       unsigned long flags;
        int ret;
 
        status = dmaengine_tx_status(chan, (dma_cookie_t)0, NULL);
        if (DMA_IN_PROGRESS == status)
                return;
 
-       spin_lock_irqsave(&sport->port.lock, flags);
        sport->tx_bytes = uart_circ_chars_pending(xmit);
-       if (sport->tx_bytes == 0) {
-               spin_unlock_irqrestore(&sport->port.lock, flags);
-               return;
-       }
 
        if (xmit->tail > xmit->head && xmit->head > 0) {
                sport->dma_tx_nents = 2;
@@ -542,7 +532,6 @@ static void dma_tx_work(struct work_struct *w)
                sport->dma_tx_nents = 1;
                sg_init_one(sgl, xmit->buf + xmit->tail, sport->tx_bytes);
        }
-       spin_unlock_irqrestore(&sport->port.lock, flags);
 
        ret = dma_map_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
        if (ret == 0) {
@@ -609,11 +598,7 @@ static void imx_start_tx(struct uart_port *port)
        }
 
        if (sport->dma_is_enabled) {
-               /*
-                * We may in the interrupt context, so arise a work_struct to
-                * do the real job.
-                */
-               schedule_work(&sport->tsk_dma_tx);
+               imx_dma_tx(sport);
                return;
        }
 
@@ -732,6 +717,7 @@ out:
        return IRQ_HANDLED;
 }
 
+static int start_rx_dma(struct imx_port *sport);
 /*
  * If the RXFIFO is filled with some data, and then we
  * arise a DMA operation to receive them.
@@ -750,7 +736,7 @@ static void imx_dma_rxint(struct imx_port *sport)
                writel(temp, sport->port.membase + UCR1);
 
                /* tell the DMA to receive the data. */
-               schedule_work(&sport->tsk_dma_rx);
+               start_rx_dma(sport);
        }
 }
 
@@ -872,22 +858,6 @@ static int imx_setup_ufcr(struct imx_port *sport, unsigned int mode)
 }
 
 #define RX_BUF_SIZE    (PAGE_SIZE)
-static int start_rx_dma(struct imx_port *sport);
-static void dma_rx_work(struct work_struct *w)
-{
-       struct imx_port *sport = container_of(w, struct imx_port, tsk_dma_rx);
-       struct tty_port *port = &sport->port.state->port;
-
-       if (sport->rx_bytes) {
-               tty_insert_flip_string(port, sport->rx_buf, sport->rx_bytes);
-               tty_flip_buffer_push(port);
-               sport->rx_bytes = 0;
-       }
-
-       if (sport->dma_is_rxing)
-               start_rx_dma(sport);
-}
-
 static void imx_rx_dma_done(struct imx_port *sport)
 {
        unsigned long temp;
@@ -919,6 +889,7 @@ static void dma_rx_callback(void *data)
        struct imx_port *sport = data;
        struct dma_chan *chan = sport->dma_chan_rx;
        struct scatterlist *sgl = &sport->rx_sgl;
+       struct tty_port *port = &sport->port.state->port;
        struct dma_tx_state state;
        enum dma_status status;
        unsigned int count;
@@ -931,8 +902,10 @@ static void dma_rx_callback(void *data)
        dev_dbg(sport->port.dev, "We get %d bytes.\n", count);
 
        if (count) {
-               sport->rx_bytes = count;
-               schedule_work(&sport->tsk_dma_rx);
+               tty_insert_flip_string(port, sport->rx_buf, count);
+               tty_flip_buffer_push(port);
+
+               start_rx_dma(sport);
        } else
                imx_rx_dma_done(sport);
 }
@@ -1014,7 +987,6 @@ static int imx_uart_dma_init(struct imx_port *sport)
                ret = -ENOMEM;
                goto err;
        }
-       sport->rx_bytes = 0;
 
        /* Prepare for TX : */
        sport->dma_chan_tx = dma_request_slave_channel(dev, "tx");
@@ -1045,11 +1017,7 @@ err:
 static void imx_enable_dma(struct imx_port *sport)
 {
        unsigned long temp;
-       struct tty_port *port = &sport->port.state->port;
 
-       port->low_latency = 1;
-       INIT_WORK(&sport->tsk_dma_tx, dma_tx_work);
-       INIT_WORK(&sport->tsk_dma_rx, dma_rx_work);
        init_waitqueue_head(&sport->dma_wait);
 
        /* set UCR1 */
@@ -1070,7 +1038,6 @@ static void imx_enable_dma(struct imx_port *sport)
 static void imx_disable_dma(struct imx_port *sport)
 {
        unsigned long temp;
-       struct tty_port *port = &sport->port.state->port;
 
        /* clear UCR1 */
        temp = readl(sport->port.membase + UCR1);
@@ -1088,7 +1055,6 @@ static void imx_disable_dma(struct imx_port *sport)
        writel(temp, sport->port.membase + UCR4);
 
        sport->dma_is_enabled = 0;
-       port->low_latency = 0;
 }
 
 /* half the RX buffer size */