Am Freitag, den 29.11.2013, 19:02 +0100 schrieb Marek Vasut:

Dear Hector Palacios,

quoted

Hi Marek,

On 11/29/2013 05:50 PM, Marek Vasut wrote:

quoted

Hello Hector,

quoted

Terminate any DMA transfer and verify the TX FIFO is empty.

Signed-off-by: Hector Palacios <redacted>
---

  drivers/tty/serial/mxs-auart.c | 23 +++++++++++++++++++++++
  1 file changed, 23 insertions(+)

diff --git a/drivers/tty/serial/mxs-auart.c

b/drivers/tty/serial/mxs-auart.c index 9f0461778fc1..d9bf6e103f65 100644

--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c

@@ -782,6 +782,28 @@ static unsigned int mxs_auart_tx_empty(struct

uart_port *u) return 0;

  }

+/*
+ * Flush the transmit buffer.
+ * Locking: called with port lock held and IRQs disabled.
+ */
+static void mxs_auart_flush_buffer(struct uart_port *u)
+{
+	struct mxs_auart_port *s = to_auart_port(u);
+	struct dma_chan *channel = s->tx_dma_chan;
+	unsigned int to;
+
+	if (auart_dma_enabled(s)) {
+		/* Avoid deadlock with the DMA engine callback */
+		spin_unlock(&s->port.lock);
+		dmaengine_terminate_all(channel);
+		spin_lock(&s->port.lock);

Can you not maybe just set some flag here to tell the DMA engine callback
things are shutting down and to don't do anything funny anymore ?

I copied these spin_lock protections from the amba-pl011.c driver.
The callbacks in the mxs-auart driver are not taking the lock but I was not
sure if any of the serial core functions they call are, so I thought it
was a good idea to take it.

It might be worth investigating this then.

quoted

quoted

quoted

+	}
+	/* Wait for the FIFO to flush */
+	to = u->timeout;
+	while (!mxs_auart_tx_empty(u) && to--)
+		mdelay(1);

Maybe you can put some cond_resched() into the loop to avoid wasting too
many cycles ?

Do you mean like this? Ok

	while (!mxs_auart_tx_empty(u) && to--) {
		cond_resched();
		mdelay(1);
	}

Yes, like that.

This path isn't timing critical. mdelay still keeps the cpu spinning,
even with a resched. Just use an absolute timeout and sleep instead of
delay.

Regards,
Lucas
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