linux-kernel - Re: [PATCH V2] cpuidle/powernv: Read target_residency value of idle states from DT if available

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Message-ID: <54C8B0E6.5080406@linux.vnet.ibm.com>
Date:	Wed, 28 Jan 2015 15:20:30 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Stewart Smith <stewart@...ux.vnet.ibm.com>, mpe@...erman.id.au
CC:	rafael.j.wysocki@...el.com, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH V2] cpuidle/powernv: Read target_residency value of idle
 states from DT if available

On 01/28/2015 02:45 PM, Stewart Smith wrote:
> Preeti U Murthy <preeti@...ux.vnet.ibm.com> writes:
>> The device tree now exposes the residency values for different idle states. Read
>> these values instead of calculating residency from the latency values. The values
>> exposed in the DT are validated for optimal power efficiency. However to maintain
>> compatibility with the older firmware code which does not expose residency
>> values, use default values as a fallback mechanism. While at it, handle some
>> cleanups.
> 
> From a "I just merged the patch that exports these values from firmware"
> point of view, using them and falling back looks good.
> 
> (I find the hardcoding of snooze in the driver a bit odd, as is the

Snooze is the only software defined idle state, the rest are platform
specific. The first idle state is usually associated with some sort of a
polling operation and each architecture has a variant to this. This is
why we end up hard-coding this idle state in the driver as far as my
understanding goes.

> hardcoding of max power states to 8 - which could bite us in the future

Hmm.. not sure about this. Need to check.

> if a future processor has more states... but these aren't problems with
> this patch)
> 
> Acked-by: Stewart Smith <stewart@...ux.vnet.ibm.com>

Thanks!

Regards
Preeti U Murthy
> 

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