[U-Boot] [PATCH 1/1 v3] omap3_beagle: Enabling UART3 first allows the Transmitter to be empty

From: Albert ARIBAUD <albert.u.boot@aribaud.net>
To: u-boot@lists.denx.de
Subject: [U-Boot] [PATCH 1/1 v3] omap3_beagle: Enabling UART3 first allows the Transmitter to be empty
Date: Fri, 29 Mar 2013 10:43:34 +0100	[thread overview]
Message-ID: <20130329104334.1958d788@lilith> (raw)
In-Reply-To: <51555CD9.9070201@arcor.de>

Hi Manfred,

On Fri, 29 Mar 2013 10:20:25 +0100, Manfred Huber <man.huber@arcor.de>
wrote:

> On some OMAP3 devices when UART3 is configured for boot mode before SPL starts 
> only THRE bit is set. We have to empty the transmitter before initialization 
> starts. This patch avoids the use of CONFIG_SYS_NS16550_BROKEN_TEMT.
> 
> Signed-off-by: Manfred Huber <man.huber@arcor.de>
> ---

Patch history is missing here.

Also, I would like the commit summary (first commit message line, also
subject of the patch mail) to clearly state what the patch *does* as
opposed to what *happens*, because it is unclear right now if you're
describing the solution or the issue. Something like :

"omap3_beagle: flush UART3 xmit on enable if TEMT is broken"

> README                     |    8 --------
>  drivers/serial/ns16550.c   |   16 ++++++++++++++--
>  include/configs/igep00x0.h |    3 ---
>  3 files changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/README b/README
> index a336476..e6b3a50 100644
> --- a/README
> +++ b/README
> @@ -616,14 +616,6 @@ The following options need to be configured:
>  		boot loader that has already initialized the UART.  Define this
>  		variable to flush the UART at init time.
>  
> -		CONFIG_SYS_NS16550_BROKEN_TEMT
> -
> -		16550 UART set the Transmitter Empty (TEMT) Bit when all output
> -		has finished and the transmitter is totally empty. U-Boot waits
> -		for this bit to be set to initialize the serial console. On some
> -		broken platforms this bit is not set in SPL making U-Boot to
> -		hang while waiting for TEMT. Define this option to avoid it.
> -
>  
>  - Console Interface:
>  		Depending on board, define exactly one serial port
> 
> diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
> index 87a0917..2922a2c 100644
> --- a/drivers/serial/ns16550.c
> +++ b/drivers/serial/ns16550.c
> @@ -36,10 +36,22 @@
>  
>  void NS16550_init(NS16550_t com_port, int baud_divisor)
>  {
> -#if (!defined(CONFIG_SYS_NS16550_BROKEN_TEMT))
> +#if (defined(CONFIG_SPL_BUILD) && defined(CONFIG_OMAP34XX))
> +	/* On some OMAP3 devices when UART3 is configured for boot mode before
> +	   SPL starts only THRE bit is set. We have to empty the transmitter
> +	   before initialization starts. */
> +	if ((serial_in(&com_port->lsr) & (UART_LSR_TEMT | UART_LSR_THRE))
> +	     == UART_LSR_THRE) {
> +		serial_out(UART_LCR_DLAB, &com_port->lcr);
> +		serial_out(baud_divisor & 0xff, &com_port->dll);
> +		serial_out((baud_divisor >> 8) & 0xff, &com_port->dlm);
> +		serial_out(UART_LCRVAL, &com_port->lcr);
> +		serial_out(0, &com_port->mdr1);
> +	}
> +#endif
> +
>  	while (!(serial_in(&com_port->lsr) & UART_LSR_TEMT))
>  		;
> -#endif
>  
>  	serial_out(CONFIG_SYS_NS16550_IER, &com_port->ier);
>  #if (defined(CONFIG_OMAP) && !defined(CONFIG_OMAP3_ZOOM2)) || \
> 
> diff --git a/include/configs/igep00x0.h b/include/configs/igep00x0.h
> index f8131b1..0617a58 100644
> --- a/include/configs/igep00x0.h
> +++ b/include/configs/igep00x0.h
> @@ -67,9 +67,6 @@
>  #define CONFIG_SYS_NS16550_REG_SIZE	(-4)
>  #define CONFIG_SYS_NS16550_CLK		V_NS16550_CLK
>  
> -/* define to avoid U-Boot to hang while waiting for TEMT */
> -#define CONFIG_SYS_NS16550_BROKEN_TEMT
> -
>  /* select serial console configuration */
>  #define CONFIG_CONS_INDEX		3
>  #define CONFIG_SYS_NS16550_COM3		OMAP34XX_UART3
> _______________________________________________
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Amicalement,
-- 
Albert.