Re: [PATCHv7] OMAP3: Serial: Improved sleep logic

[Kevin Hilman <khilman@deeprootsystems.com>]

Kevin Hilman <khilman@deeprootsystems.com> writes:

> Tero Kristo <tero.kristo@nokia.com> writes:
>
>> From: Tero Kristo <tero.kristo@nokia.com>
>>
>> This patch contains following improvements:
>> - Only RX interrupt will now kick the sleep prevent timer
>> - TX fifo status is checked before disabling clocks, this will prevent
>>   on-going transmission to be cut
>> - Smartidle is now enabled/disabled only while switching clocks, as having
>>   smartidle enabled while RX/TX prevents any wakeups from being received
>>   from UART module
>> - Added workqueue for wakeup checks, as jiffy timer access within the
>>   idle loop results into skewed timers as jiffy timers are stopped
>> - Added garbage_timer for ignoring the first character received during
>>   the first tick after clock enable, this prevents garbage characters to be
>>   received in low sleep states
>> - omap_uart_enable_irqs() changed to use enable_irq / disable_irq instead
>>   of request / free. Using request/free changes the behavior after first
>>   suspend due to reversed interrupt handler ordering
>
> Hi Tero,
>
> FYI... I had to make one additional change (diff below) to this patch
> after discovering a regression pointed out by Peter Tseng.
>
> If the UART timeouts are disabled (set to zero), which they are by
> default, and you suspend the system, the UART would not be usable
> after wakeup.   Simply enabling a timeout was fixing the problem.
>
> I tracked the problem to the garbage timer being enabled even when
> the UART timeout was not enabled.  Since the garbage_ignore flag
> is only ever cleared when a uart->timeout is set, the garbage
> timer was never being disabled, effectively disabling the UART.
>
> I've folded this fix below into your patch in the pm-fixes branch
> and pushed a new PM branch.

OK, I'm dropping this patch from the PM branch.  It has caused me more
problems that it has solved so far, and I just noticed that
UART2-based consoles (n900, beagle) stop working all together when I
enable UART timeouts with this patch.  Seems to be again related to
the garbage timer.

What I would like to see instead is UART hwmods finished and the
omap-serial driver merged so that we can start moving this PM logic
into the omap-serial driver using the runtime PM layer.

Kevin

>
>
> diff --git a/arch/arm/mach-omap2/serial.c b/arch/arm/mach-omap2/serial.c
> index b731556..b709cf8 100644
> --- a/arch/arm/mach-omap2/serial.c
> +++ b/arch/arm/mach-omap2/serial.c
> @@ -396,7 +396,8 @@ void omap_uart_prepare_idle(int num)
>  
>  static void serial_wakeup(struct omap_uart_state *uart)
>  {
> -	uart->garbage_ignore = 1;
> +	if (uart->timeout)
> +		uart->garbage_ignore = 1;
>  	schedule_work(&uart->wakeup_work);
>  }
>  
> k