Subject: [PATCH] serial/imx: check that the buffer is non-empty before sending it out

From: [email-masked] (Daniel Mack)
Date: Thu, 14 Oct 2010 13:27:35 +0200

On Wed, Oct 13, 2010 at 11:03:57AM +0200, Uwe Kleine-K?nig wrote:
> From: Volker Ernst <[email-masked]>
> 
> The .start_tx callback (imx_start_tx here) isn't only called when the
> buffer is non-empty.  E.g. after resume or when handshaking is enabled
> and the other side starts to signal being ready.
> 
> So check for an empty puffer already before sending the first character.
> This prevents sending out stale (or uninitialised) data.
> 
> Signed-off-by: Volker Ernst <[email-masked]>
> Signed-off-by: Daniel Mack <[email-masked]>
> Cc: Andy Green <[email-masked]>
> [ukl: reword commit log, put check in while condition]
> Signed-off-by: Uwe Kleine-K?nig <[email-masked]>
> ---
> Hello,
> 
> as I didn't sent a patch, here comes my current version.  Don't know if
> it makes it easier to test for you ...
> 
> I faked Daniel's SoB as Andrew said he did, compressed the changelog a
> bit and put the check in the while condition as I suggested.

FWIW, that looks good to me. Thanks for finishing the work :)

Daniel

>  drivers/serial/imx.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/serial/imx.c b/drivers/serial/imx.c
> index 66ecc7a..dfcf4b1 100644
> --- a/drivers/serial/imx.c
> +++ b/drivers/serial/imx.c
> @@ -327,14 +327,13 @@ 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)) {
> +	while (!uart_circ_empty(xmit) &&
> +			!(readl(sport->port.membase + UTS) & UTS_TXFULL)) {
>  		/* 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)
> -- 
> 1.7.2.3
> 
> 
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