Subject: [PATCH] ARM: imx serial driver: fix resume

From: [email-masked] (Daniel Mack)
Date: Tue, 12 Oct 2010 20:32:39 +0200

On Tue, Oct 12, 2010 at 07:56:58PM +0200, Uwe Kleine-K?nig wrote:
> On Wed, Oct 06, 2010 at 06:57:16PM +0200, Daniel Mack wrote:
> > From: Volker Ernst <[email-masked]>
> > 
> > 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 <[email-masked]>
> > Cc: Daniel Mack <[email-masked]>
> > Cc: Andy Green <[email-masked]>
> > ---
> > 
> > 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.

Ok, thanks. However, I can not test this myself - Volker, can you try
the patch Uwe sent along some days ago?

Thanks,
Daniel