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>

1 files changed, 10 insertions, 44 deletions

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 13c2c2d09cac..bb84f8d4c54e 100644
--- 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 */