[PATCH 10/11] SERIAL: omap: fix MCR TCRTLR bit handling

[Russell King - ARM Linux]

On Tue, Oct 16, 2012 at 12:01:06PM +0100, Russell King wrote:
> The MCR TCRTLR bit can only be changed when ECB is set in the EFR.
> Unfortunately, several places were trying to alter this bit while ECB
> was clear:
> 
> - serial_omap_configure_xonxoff() was attempting to clear the bit after
>   explicitly clearing the ECB bit.
> - serial_omap_set_termios() was trying the same trick after setting the
>   SCR, and when trying to change the TCR register when hardware flow
>   control was enabled.
> 
> Fix this by ensuring that we always have ECB set whenever the TCRTLR bit
> is changed.
> 
> Moreover, we start out by reading the EFR and MCR registers, which may
> have indeterminent bit settings for the ECB and TCRTLR bits.  Ensure
> that these bits always start off in a known state.

Note - this patch unfortunately exposes some of the bugs in their full
glory as we now write to the correct registers and actually end up
programming the hardware correctly.

I've reduced the window as far as possible by putting this one next to
patch 11 which fixes it, but no amount of reordering can hide some kind
of breakage along the way.

> Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> ---
>  drivers/tty/serial/omap-serial.c |   32 ++++++++++++++++++--------------
>  1 files changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 537829f..7cc151c 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -706,9 +706,10 @@ serial_omap_configure_xonxoff
>  	serial_out(up, UART_MCR, up->mcr | UART_MCR_TCRTLR);
>  	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
>  	serial_out(up, UART_TI752_TCR, OMAP_UART_TCR_TRIG);
> -	serial_out(up, UART_EFR, up->efr);
>  	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_A);
>  	serial_out(up, UART_MCR, up->mcr & ~UART_MCR_TCRTLR);
> +	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
> +	serial_out(up, UART_EFR, up->efr);
>  	serial_out(up, UART_LCR, up->lcr);
>  }
>  
> @@ -729,7 +730,6 @@ serial_omap_set_termios(struct uart_port *port, struct ktermios *termios,
>  {
>  	struct uart_omap_port *up = to_uart_omap_port(port);
>  	unsigned char cval = 0;
> -	unsigned char efr = 0;
>  	unsigned long flags = 0;
>  	unsigned int baud, quot;
>  
> @@ -839,12 +839,12 @@ serial_omap_set_termios(struct uart_port *port, struct ktermios *termios,
>  
>  	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
>  
> -	up->efr = serial_in(up, UART_EFR);
> +	up->efr = serial_in(up, UART_EFR) & ~UART_EFR_ECB;
>  	up->efr &= ~UART_EFR_SCD;
>  	serial_out(up, UART_EFR, up->efr | UART_EFR_ECB);
>  
>  	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_A);
> -	up->mcr = serial_in(up, UART_MCR);
> +	up->mcr = serial_in(up, UART_MCR) & ~UART_MCR_TCRTLR;
>  	serial_out(up, UART_MCR, up->mcr | UART_MCR_TCRTLR);
>  	/* FIFO ENABLE, DMA MODE */
>  
> @@ -863,9 +863,12 @@ serial_omap_set_termios(struct uart_port *port, struct ktermios *termios,
>  
>  	serial_out(up, UART_OMAP_SCR, up->scr);
>  
> -	serial_out(up, UART_EFR, up->efr);
> +	/* Reset UART_MCR_TCRTLR: this must be done with the EFR_ECB bit set */
>  	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_A);
>  	serial_out(up, UART_MCR, up->mcr);
> +	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
> +	serial_out(up, UART_EFR, up->efr);
> +	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_A);
>  
>  	/* Protocol, Baud Rate, and Interrupt Settings */
>  
> @@ -904,20 +907,21 @@ serial_omap_set_termios(struct uart_port *port, struct ktermios *termios,
>  	/* Hardware Flow Control Configuration */
>  
>  	if (termios->c_cflag & CRTSCTS) {
> -		efr |= (UART_EFR_CTS | UART_EFR_RTS);
> -		serial_out(up, UART_LCR, UART_LCR_CONF_MODE_A);
> -
> -		up->mcr = serial_in(up, UART_MCR);
> -		serial_out(up, UART_MCR, up->mcr | UART_MCR_TCRTLR);
> -
> +		/* Enable access to TCR/TLR */
>  		serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
> -		up->efr = serial_in(up, UART_EFR);
>  		serial_out(up, UART_EFR, up->efr | UART_EFR_ECB);
> +		serial_out(up, UART_LCR, UART_LCR_CONF_MODE_A);
> +		serial_out(up, UART_MCR, up->mcr | UART_MCR_TCRTLR);
>  
>  		serial_out(up, UART_TI752_TCR, OMAP_UART_TCR_TRIG);
> -		serial_out(up, UART_EFR, efr); /* Enable AUTORTS and AUTOCTS */
> -		serial_out(up, UART_LCR, UART_LCR_CONF_MODE_A);
> +
> +		/* Enable AUTORTS and AUTOCTS */
> +		up->efr |= UART_EFR_CTS | UART_EFR_RTS;
> +
> +		/* Disable access to TCR/TLR */
>  		serial_out(up, UART_MCR, up->mcr | UART_MCR_RTS);
> +		serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
> +		serial_out(up, UART_EFR, up->efr);
>  		serial_out(up, UART_LCR, cval);
>  	} else {
>  		/* Disable AUTORTS and AUTOCTS */
> -- 
> 1.7.4.4
> 
> 
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