Re: [PATCH] OMAP3: Serial: Improved sleep logic

[Tony Lindgren <tony@atomide.com>]

* Tero.Kristo@nokia.com <Tero.Kristo@nokia.com> [100203 23:59]:
>  
> 
> >-----Original Message-----
> >From: ext Tony Lindgren [mailto:tony@atomide.com] 
> >Sent: 03 February, 2010 19:50
> >To: Kristo Tero (Nokia-D/Tampere)
> >Cc: linux-omap@vger.kernel.org
> >Subject: Re: [PATCH] OMAP3: Serial: Improved sleep logic
> >
> >* Tero Kristo <tero.kristo@nokia.com> [100202 01:38]:
> >> From: Tero Kristo <tero.kristo@nokia.com>
> >> 
> >> Only RX interrupt will now kick the sleep prevent timer. In 
> >addition, TX
> >> fifo status is checked before disabling clocks, this will 
> >prevent occasional
> >> garbage being printed on serial line. Smartidle is also 
> >disabled while
> >> entering idle if we have data in the transmit buffer, 
> >because having this
> >> enabled will prevent wakeups from the TX interrupt, and this causes
> >> pauses while sending large blocks of data.
> >
> >Sounds this is for 2.6.34 merge window and does not contain anything
> >that needs to be fixed for 2.6.33. 
> 
> Yeah, this only fixes a couple of annoying issues, but nothing fatal. Also improves power efficiency in some cases which is a nice to have feature, and basically eases the development of PM code as the UART does not block the system from sleeping always.

Yeah cool. Separate issue, but I wonder if we should also clear
the the first rx character from the fifo to avoid corrupting
the console. Only when the uart clocks are off and and
we get a key press. Would be easy to do just do with one
serial_read_reg(uart->p, UART_RX)..

Tony

> 
> -Tero
> 
> >
> >Regards,
> >
> >Tony
> >
> > 
> >> Signed-off-by: Tero Kristo <tero.kristo@nokia.com>
> >> ---
> >>  arch/arm/mach-omap2/serial.c |   19 +++++++++++++++----
> >>  1 files changed, 15 insertions(+), 4 deletions(-)
> >> 
> >> diff --git a/arch/arm/mach-omap2/serial.c 
> >b/arch/arm/mach-omap2/serial.c
> >> index 777e802..e11dfe9 100644
> >> --- a/arch/arm/mach-omap2/serial.c
> >> +++ b/arch/arm/mach-omap2/serial.c
> >> @@ -317,7 +317,8 @@ static void omap_uart_allow_sleep(struct 
> >omap_uart_state *uart)
> >>  	if (!uart->clocked)
> >>  		return;
> >>  
> >> -	omap_uart_smart_idle_enable(uart, 1);
> >> +	if (serial_read_reg(uart->p, UART_LSR) & UART_LSR_TEMT)
> >> +		omap_uart_smart_idle_enable(uart, 1);
> >>  	uart->can_sleep = 1;
> >>  	del_timer(&uart->timer);
> >>  }
> >> @@ -335,7 +336,11 @@ void omap_uart_prepare_idle(int num)
> >>  
> >>  	list_for_each_entry(uart, &uart_list, node) {
> >>  		if (num == uart->num && uart->can_sleep) {
> >> -			omap_uart_disable_clocks(uart);
> >> +			if (serial_read_reg(uart->p, UART_LSR) &
> >> +					UART_LSR_TEMT)
> >> +				omap_uart_disable_clocks(uart);
> >> +			else
> >> +				omap_uart_smart_idle_enable(uart, 0);
> >>  			return;
> >>  		}
> >>  	}
> >> @@ -407,8 +412,14 @@ int omap_uart_can_sleep(void)
> >>  static irqreturn_t omap_uart_interrupt(int irq, void *dev_id)
> >>  {
> >>  	struct omap_uart_state *uart = dev_id;
> >> +	u8 lsr;
> >>  
> >> -	omap_uart_block_sleep(uart);
> >> +	lsr = serial_read_reg(uart->p, UART_LSR);
> >> +	/* Check for receive interrupt */
> >> +	if (lsr & UART_LSR_DR)
> >> +		omap_uart_block_sleep(uart);
> >> +	if (lsr & UART_LSR_TEMT && uart->can_sleep)
> >> +		omap_uart_smart_idle_enable(uart, 1);
> >>  
> >>  	return IRQ_NONE;
> >>  }
> >> -- 
> >> 1.5.4.3
> >> 
> >> --
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