Re: [PATCH] Fix polling policy in the absence of _TZP

[Len Brown <lenb@kernel.org>]

On Tuesday 13 May 2008, Matthew Garrett wrote:
> Fix Linux to conform to 11.3.18 of the ACPI spec 3.0. In the absence of 
> a _TZP method, we should be polling at a default frequency. While it can 
> be argued that "0" is a default frequency, I don't think that's what the 
> spec authors had in mind.

Actually it is what the spec authors had in mind,
and the spec is wrong.  Yes, I can provide documentation
supporting this statement.

NAK

thanks,
-Len

> Signed-off-by: Matthew Garrett <mjg@redhat.com>
> 
> ---
> 
> Arguably this should be implemented in such a way that the polling rate 
> increases as the temperature rises and drops if the trend is downwards. 
> That would give higher resolution when we're heading towards a trip 
> point, without any significant increase in power consumption since 
> increased temperatures imply that the CPU is probably not idle.
> 
> diff --git a/drivers/acpi/thermal.c b/drivers/acpi/thermal.c
> index 504385b..93cb3e8 100644
> --- a/drivers/acpi/thermal.c
> +++ b/drivers/acpi/thermal.c
> @@ -846,10 +846,11 @@ static void acpi_thermal_check(void *data)
>  	 * Calculate Sleep Time
>  	 * --------------------
>  	 * If we're in the passive state, use _TSP's value.  Otherwise
> -	 * use the default polling frequency (e.g. _TZP).  If no polling
> -	 * frequency is specified then we'll wait forever (at least until
> -	 * a thermal event occurs).  Note that _TSP and _TZD values are
> -	 * given in 1/10th seconds (we must covert to milliseconds).
> +	 * use the default polling frequency (e.g. _TZP).  If no
> +	 * polling frequency is specified then we'll wait 10 seconds
> +	 * (or until a thermal event occurs).  Note that _TSP and _TZD
> +	 * values are given in 1/10th seconds (we must covert to
> +	 * milliseconds).
>  	 */
>  	if (tz->state.passive) {
>  		sleep_time = tz->trips.passive.tsp * 100;
> @@ -1575,8 +1576,9 @@ static int acpi_thermal_get_info(struct acpi_thermal *tz)
>  	/* Get default polling frequency [_TZP] (optional) */
>  	if (tzp)
>  		tz->polling_frequency = tzp;
> -	else
> -		acpi_thermal_get_polling_frequency(tz);
> +	else if (acpi_thermal_get_polling_frequency(tz) == -ENODEV)
> +		/* If no _TZP, default to polling every 10 seconds */
> +		tz->polling_frequency = 100;
>  
>  	return 0;
>  }
>