Subject: [PATCH v6 10/16] OMAP2+: UART: Modify omap_uart_can_sleep function

From: [email-masked] (Kevin Hilman)
Date: Tue, 11 Oct 2011 11:24:46 -0700

"Govindraj.R" <[email-masked]> writes:

> Modify the omap_uart_can_sleep function to check uart is active
> or not to be used by pm code to enter low power states.

Doesn't the driver now control when the UART clocks are gated (using
runtime PM autosuspend)?

IMO, this check should be completely removed and the driver should
be managing this with the autosuspend timeout.

> Removing this check can cause console response little sluggish.

Sluggish in what way?

If the driver is runtime suspended, it should only be sluggish for the
first character.  After that, the autosuspend timeout should prevent it
from feeling sluggish.

> However no characters will be lost until uart clocks are gated
> and woken up using rx-pad. UART interface clocks can be auto gated
> this can make response on uart slower. This behaviour was observed
> only on some of OMAP3 boards(beagleboard xm rev c).
>
> Reported-by: Tero Kristo <[email-masked]>
> Signed-off-by: Govindraj.R <[email-masked]>
> ---
>  arch/arm/mach-omap2/serial.c |   21 +++++++++------------
>  1 files changed, 9 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm/mach-omap2/serial.c b/arch/arm/mach-omap2/serial.c
> index 6725caf..ccf3550 100644
> --- a/arch/arm/mach-omap2/serial.c
> +++ b/arch/arm/mach-omap2/serial.c
> @@ -156,23 +156,20 @@ static void omap_uart_smart_idle_enable(struct omap_uart_state *uart,
>  
>  int omap_uart_can_sleep(void)
>  {
> -	struct omap_uart_state *uart;
> -	int can_sleep = 1;
> -
> -	list_for_each_entry(uart, &uart_list, node) {
> -		if (!uart->clocked)
> -			continue;
> +	struct omap_hwmod *oh;
> +	u8 i, ret = true;
>  
> -		if (!uart->can_sleep) {
> -			can_sleep = 0;
> +	for (i = 0; i < num_uarts; i++) {
> +		oh = omap_uart_hwmod_lookup(i);

This is a heavy operation to add for *every* entry into idle.

> +		if (!oh)
>  			continue;
> -		}
>  
> -		/* This UART can now safely sleep. */
> -		omap_uart_allow_sleep(uart);
> +		if (oh->od && oh->od->pdev &&
> +				!pm_runtime_suspended(&oh->od->pdev->dev))
> +			return false;
>  	}
>  
> -	return can_sleep;
> +	return ret;
>  }
>  
>  #ifdef CONFIG_OMAP_MUX

Kevin