From mboxrd@z Thu Jan  1 00:00:00 1970
From: u.kleine-koenig@pengutronix.de (Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=)
Date: Wed, 2 Oct 2013 14:22:22 +0200
Subject: [PATCH v2 2/2] serial: mxs-auart: wait for FIFO to flush before
 shutdown
In-Reply-To: <1380715364-8025-3-git-send-email-hector.palacios@digi.com>
References: <1380715364-8025-1-git-send-email-hector.palacios@digi.com>
 <1380715364-8025-3-git-send-email-hector.palacios@digi.com>
Message-ID: <20131002122222.GQ2548@pengutronix.de>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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@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 ...

Best regards
Uwe

>  	if (auart_dma_enabled(s))
>  		mxs_auart_dma_exit(s);
> -- 
> 1.8.4
> 
> 

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |