[PATCH] ARM: imx serial driver: fix resume

[u.kleine-koenig@pengutronix.de (Uwe Kleine-König)]

Hallo Daniel und Volker,

On Wed, Oct 06, 2010 at 06:57:16PM +0200, Daniel Mack wrote:
> From: Volker Ernst <volker.ernst@txtr.com>
> 
> I just came across a bug in the IMX31 serial driver which is still
> present in the newest kernels and which prevents successful
> resume-operation for the IMX31 serial ports.
> 
> What happens is that in "drivers/serial/imx.c" on resume function
> "serial_imx_resume" gets called. This function in turn calls
> "uart_resume_port" (in the generic serial driver "serial_core.c"),
> which in turn calls "imx_start_tx" in "imx.c" (in case the SIO-port
> was really suspended) which in turn calls "imx_transmit_buffer".
> 
> However calling "imx_transmit_buffer" with an empty TX-fifo (as is
> usually the case) will result in the serial port starting to transmit
> (actually the old [already sent] tx-buffer), as there is no check if
> the tx-buffer is empty before starting to feed tx-fifo-data to the
> serial port hardware.
> 
> Signed-off-by: Volker Ernst <volker.ernst@txtr.com>
> Cc: Daniel Mack <daniel@caiaq.de>
> Cc: Andy Green <andy@warmcat.com>
> ---
> 
> Volker did all the work on this, he just doesn't want to push his great
> contributions upstream, so I do it for him :)
> 
> 
>  drivers/serial/imx.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/serial/imx.c b/drivers/serial/imx.c
> index 66ecc7a..0170119 100644
> --- a/drivers/serial/imx.c
> +++ b/drivers/serial/imx.c
> @@ -328,13 +328,13 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
>  	struct circ_buf *xmit = &sport->port.state->xmit;
>  
>  	while (!(readl(sport->port.membase + UTS) & UTS_TXFULL)) {
> +		if (uart_circ_empty(xmit))
> +			break;
>  		/* send xmit->buf[xmit->tail]
>  		 * out the port here */
>  		writel(xmit->buf[xmit->tail], sport->port.membase + URTX0);
>  		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
>  		sport->port.icount.tx++;
> -		if (uart_circ_empty(xmit))
> -			break;
>  	}
>  
>  	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
I needed that patch now, too, though in a different situation.  I havn't
investigated the details yet, but I think the problem is that
imx_transmit_buffer is called, too, when using handshaking and the other
side starts to be ready.

You can count that as an Acked-by: me, preferably with the check added
to the while condition as suggested in a different mail of this thread.

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-K?nig            |
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