From mboxrd@z Thu Jan  1 00:00:00 1970
From: swarren@wwwdotorg.org (Stephen Warren)
Date: Thu, 18 Jul 2013 13:26:56 -0600
Subject: [PATCH 3/4] pinctrl: Add support for additional dynamic states
In-Reply-To: <20130718073638.GP7656@atomide.com>
References: <20130716090310.5541.36777.stgit@localhost>
 <20130716090536.5541.36289.stgit@localhost> <51E70B5D.6030802@wwwdotorg.org>
 <20130718073638.GP7656@atomide.com>
Message-ID: <51E84180.6080902@wwwdotorg.org>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 07/18/2013 01:36 AM, Tony Lindgren wrote:
> * Stephen Warren <swarren@wwwdotorg.org> [130717 14:30]:
>> On 07/16/2013 03:05 AM, Tony Lindgren wrote:
...
>> Why shouldn't e.g. a pinctrl-based I2C mux also be able to do runtime
>> PM? Does the mux setting select which states are used for runtime PM, or
>> does runtime PM override the basic mux setting, or must the pincrl-I2C
>> mux manually implement custom runtime-PM/pinctrl interaction since
>> there's no generic answer to those questions? How many more custom
>> exceptions will there be?
> 
> The idea is that runtime PM will never touch the basic mux settings
> at all. The "default" state should be considered a static state
> that is claimed during driver probe, and released when the driver
> is unloaded. This is typically let's say 90% of the pins for any
> device.
> 
> For runtime PM, we can just toggle the PM related pinctrl states as
> they have been verified to match the active state during init.
> 
> So I don't see why pinctrl-I2C would have to do anything specific.
> All that is required is that the pins are grouped for the consumer
> driver, and we can provide some automated checks on the states for
> runtime PM.

So, consider a pinctrl-based I2C mux. It has 2 states to cover two I2C
buses:

a) bus 1: I2C controller is muxed out onto one set of pins.

b) bus 2: I2C controller is muxed out onto another set of pins.

Now, the system could go idle in either of those 2 states, and then
later need to return to one of those states. I just don't see how that
would work, since the runtime PM code in this series switches to *an*
active state when the device becomes non-idle. If the definition of the
idle state switches the mux function for both sets of pins to some
idle/quiescent value, then you'd need to do different reprogramming when
going back to "the" active state; I guess the system would need to
remember which state was active before switching to idle, then switch
back to that same state rather than hard-coding the active state name as
"active"...