RE: [PATCH 1/2] serial: imx: remove the DMA wait queue

From: Wang, Jiada (ESD)
Date: Fri May 30 2014 - 05:27:37 EST


Hi Shijie

After apply this patch into our kernel,
We are facing data hang issue when sending big size file (2M used in test) to uart port
Note: Rx port is also keep receiving data.

After read the implementation of uart_stop(),
I feel like, stop_tx() is used to perform flow control when like a XOFF is received.
Which means no data should be dropped, as they may need to be sent out,
When next start_tx() is called.

But by calling dmaengine_termiate_all(), the data already be submitted to DMA engine,
May be lost, thus cause data hang.

What do you think?

Thanks,
Jiada

-----Original Message-----
From: linux-arm-kernel [mailto:linux-arm-kernel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Huang Shijie
Sent: Friday, May 23, 2014 1:33 PM
To: gregkh@xxxxxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Huang Shijie; linux-kernel@xxxxxxxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx
Subject: [PATCH 1/2] serial: imx: remove the DMA wait queue

The DMA wait queue makes the code very complicated:
For RX, the @->stop_rx hook does not really stop the RX;
For TX, the @->stop_tx hook does not really stop the TX.

The above make the imx_shutdown has to wait the RX/TX DMA to be finished.

In order to make code more simple, this patch removes the DMA wait queue.
By calling the dmaengine_terminate_all, this patch makes the RX stops immediately after we call the @->stop_rx hook, so does the TX.

Signed-off-by: Huang Shijie <b32955@xxxxxxxxxxxxx>
---
drivers/tty/serial/imx.c | 42 ++++++++++++++----------------------------
1 files changed, 14 insertions(+), 28 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index d1f16d3..ed6cdf7 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -225,7 +225,6 @@ struct imx_port {
void *rx_buf;
unsigned int tx_bytes;
unsigned int dma_tx_nents;
- wait_queue_head_t dma_wait;
unsigned int saved_reg[11];
};

@@ -417,12 +416,10 @@ static void imx_stop_tx(struct uart_port *port)
return;
}

- /*
- * We are maybe in the SMP context, so if the DMA TX thread is running
- * on other cpu, we have to wait for it to finish.
- */
- if (sport->dma_is_enabled && sport->dma_is_txing)
- return;
+ if (sport->dma_is_enabled && sport->dma_is_txing) {
+ dmaengine_terminate_all(sport->dma_chan_tx);
+ sport->dma_is_txing = 0;
+ }

temp = readl(sport->port.membase + UCR1);
writel(temp & ~UCR1_TXMPTYEN, sport->port.membase + UCR1); @@ -436,12 +433,10 @@ static void imx_stop_rx(struct uart_port *port)
struct imx_port *sport = (struct imx_port *)port;
unsigned long temp;

- /*
- * We are maybe in the SMP context, so if the DMA TX thread is running
- * on other cpu, we have to wait for it to finish.
- */
- if (sport->dma_is_enabled && sport->dma_is_rxing)
- return;
+ if (sport->dma_is_enabled && sport->dma_is_rxing) {
+ dmaengine_terminate_all(sport->dma_chan_rx);
+ sport->dma_is_rxing = 0;
+ }

temp = readl(sport->port.membase + UCR2);
writel(temp & ~UCR2_RXEN, sport->port.membase + UCR2); @@ -498,12 +493,6 @@ static void dma_tx_callback(void *data)
dev_dbg(sport->port.dev, "we finish the TX DMA.\n");

uart_write_wakeup(&sport->port);
-
- if (waitqueue_active(&sport->dma_wait)) {
- wake_up(&sport->dma_wait);
- dev_dbg(sport->port.dev, "exit in %s.\n", __func__);
- return;
- }
}

static void imx_dma_tx(struct imx_port *sport) @@ -876,10 +865,6 @@ static void imx_rx_dma_done(struct imx_port *sport)
writel(temp, sport->port.membase + UCR1);

sport->dma_is_rxing = 0;
-
- /* Is the shutdown waiting for us? */
- if (waitqueue_active(&sport->dma_wait))
- wake_up(&sport->dma_wait);
}

/*
@@ -1026,8 +1011,6 @@ static void imx_enable_dma(struct imx_port *sport) {
unsigned long temp;

- init_waitqueue_head(&sport->dma_wait);
-
/* set UCR1 */
temp = readl(sport->port.membase + UCR1);
temp |= UCR1_RDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN | @@ -1219,10 +1202,13 @@ static void imx_shutdown(struct uart_port *port)
unsigned long flags;

if (sport->dma_is_enabled) {
- /* We have to wait for the DMA to finish. */
- wait_event(sport->dma_wait,
- !sport->dma_is_rxing && !sport->dma_is_txing);
+ /*
+ * The upper layer may does not call the @->stop_tx and
+ * @->stop_rx, so we call them ourselves.
+ */
+ imx_stop_tx(port);
imx_stop_rx(port);
+
imx_disable_dma(sport);
imx_uart_dma_exit(sport);
}
--
1.7.8


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