[PATCH] ARM: imx serial driver: fix resume
Uwe Kleine-König
u.kleine-koenig at pengutronix.de
Tue Oct 12 13:56:58 EDT 2010
Hallo Daniel und Volker,
On Wed, Oct 06, 2010 at 06:57:16PM +0200, Daniel Mack wrote:
> From: Volker Ernst <volker.ernst at 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 at txtr.com>
> Cc: Daniel Mack <daniel at caiaq.de>
> Cc: Andy Green <andy at 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
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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