[PATCH v2 2/2] serial: mxs-auart: wait for FIFO to flush before shutdown

[Hector Palacios]

Hello Uwe,

On 10/02/2013 02:22 PM, Uwe Kleine-König wrote:
> Hello Hector,
>
> On Wed, Oct 02, 2013 at 02:02:44PM +0200, Hector Palacios wrote:
>> The shutdown function was not waiting for the FIFO (which may be the
>> real 16 byte FIFO or the DMA buffer, if DMA is enabled) to flush
>> before disabling the AUART.
>> This lead to many bytes not being transferred (specially at low
>> baudrates), as they were still in the DMA buffer when the AUART was
>> shutdown.
>> This patch also adds the check for the BUSY flag before disabling
>> the AUART.
>>
>> Signed-off-by: Hector Palacios <hector.palacios at digi.com>
>> ---
>>   drivers/tty/serial/mxs-auart.c | 13 +++++++++++++
>>   1 file changed, 13 insertions(+)
>>
>> diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
>> index 9f046177..589b595 100644
>> --- a/drivers/tty/serial/mxs-auart.c
>> +++ b/drivers/tty/serial/mxs-auart.c
>> @@ -757,9 +757,22 @@ static int mxs_auart_startup(struct uart_port *u)
>>   	return 0;
>>   }
>>
>> +static unsigned int mxs_auart_tx_empty(struct uart_port *u);
>> +
>>   static void mxs_auart_shutdown(struct uart_port *u)
>>   {
>>   	struct mxs_auart_port *s = to_auart_port(u);
>> +	unsigned int to;
>> +
>> +	/* Wait for the FIFO to flush */
>> +	to = u->timeout;
>> +	while (!mxs_auart_tx_empty(u) && to--)
>> +		mdelay(1);
>> +
>> +	/* Wait for UART to become idle ... */
>> +	to = u->timeout;
>> +	while ((readl(u->membase + AUART_STAT) & AUART_STAT_BUSY) && to--)
>> +		mdelay(1);
> If the 2nd loop is needed the tx_empty callback is buggy. According to
> Documentation/serial/driver tx_empty "tests whether the transmitter fifo
> and shifter for the port [...] is empty". I guess it only tests for the
> fifo part? Time for another fix ...

Do you mean the tx_empty should check both for TX_FIFO and !BUSY, right?
I did it so because I thought the BUSY was also set during rx, but it is really only 
used to signal tx operation.

That would turn this patch into this:

@@ -755,13 +755,21 @@ static int mxs_auart_startup(struct uart_port *u)
  	writel(AUART_LINECTRL_FEN, u->membase + AUART_LINECTRL_SET);

  	return 0;
  }

+static unsigned int mxs_auart_tx_empty(struct uart_port *u);
+
  static void mxs_auart_shutdown(struct uart_port *u)
  {
  	struct mxs_auart_port *s = to_auart_port(u);
+	unsigned int to;
+
+	/* Wait for the FIFO to flush */
+	to = u->timeout;
+	while (!mxs_auart_tx_empty(u) && to--)
+		mdelay(1);

  	if (auart_dma_enabled(s))
  		mxs_auart_dma_exit(s);

  	writel(AUART_CTRL2_UARTEN, u->membase + AUART_CTRL2_CLR);
@@ -774,14 +782,15 @@ static void mxs_auart_shutdown(struct uart_port *u)
  	clk_disable_unprepare(s->clk);
  }

  static unsigned int mxs_auart_tx_empty(struct uart_port *u)
  {
-	if (readl(u->membase + AUART_STAT) & AUART_STAT_TXFE)
-		return TIOCSER_TEMT;
-	else
-		return 0;
+	if (!((readl(u->membase + AUART_STAT) & AUART_STAT_BUSY)))
+		if (readl(u->membase + AUART_STAT) & AUART_STAT_TXFE)
+			return TIOCSER_TEMT;
+
+	return 0;
  }

  static void mxs_auart_start_tx(struct uart_port *u)
  {
  	struct mxs_auart_port *s = to_auart_port(u);


Do you agree?

Best regards,
--
Hector Palacios