[U-Boot] [PATCH] omap3_beagle: Enable CONFIG_SYS_NS16550_BROKEN_TEMT

Scott Wood
2013-03-21T22:28:30Z

On 03/21/2013 05:21:00 PM, Tom Rini wrote:
> On Thu, Mar 21, 2013 at 08:03:59PM +0100, Manfred Huber wrote:
> > From: Manfred Huber
> >
> > Beagleboard UART (ns16550) doesn't set the Transmitter Empty (TEMT)
> > Bit in SPL.

The serial port behaves differently based on the stage of U-Boot that
is running?

Or is it that the bit doesn't get set until the port has been properly
initialized? Couldn't that happen in a case where SPL isn't used at
all?

> > Only Transmitter Hold Register Empty (THRE) Bit is set.
> > This makes SPL to hang while waiting for TEMT. Adding the
> > CONFIG_SYS_NS16550_BROKEN_TEMT config option and waiting for THRE
> > avoid this issue.
> >
> > Signed-off-by: Manfred Huber <man.huber@arcor.de>
> > ---
> > drivers/serial/ns16550.c | 5 ++++-
> > include/configs/omap3_beagle.h | 3 +++
> > 2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
> > index b2da8b3..6379bcc 100644
> > --- a/drivers/serial/ns16550.c
> > +++ b/drivers/serial/ns16550.c
> > @@ -36,7 +36,10 @@
> >
> > void NS16550_init(NS16550_t com_port, int baud_divisor)
> > {
> > -#if (!defined(CONFIG_SYS_NS16550_BROKEN_TEMT))
> > +#if defined(CONFIG_SPL_BUILD) &&
> defined(CONFIG_SYS_NS16550_BROKEN_TEMT)
> > + while (!(serial_in(&com_port->lsr) & UART_LSR_THRE))
> > + ;
> > +#else
> > while (!(serial_in(&com_port->lsr) & UART_LSR_TEMT))
> > ;
> > #endif
>
> Scott, do you still have access to the failing systems that made us
> introduce this change to start with?

It was an intermittent failure seen on a development tree, so not
really. You could try testing it by printing something immediately
before calling NS16550_init(), either in a situation where you know the
serial port is already configured (e.g. by SPL) or by calling
NS16550_init() twice.

> Could we perhaps go with the THRE test instead in all cases? Thanks!

Wouldn't that still allow the last character to possibly be corrupted?

-Scott