Date:	Tue, 20 May 2014 12:42:18 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	FanWu <fwu@...vell.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	ext Tony Lindgren <tony@...mide.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephen Warren <swarren@...dia.com>,
	Chao Xie <cxie4@...vell.com>, Yilu Mao <ylmao@...vell.com>,
	Ning Jiang <njiang1@...vell.com>,
	Xiaofan Tian <tianxf@...vell.com>,
	Fangsuo Wu <fswu@...vell.com>
Subject: Re: [PATCH] pinctrl: add params in disable_setting for different
 usage

On 05/19/2014 09:05 PM, FanWu wrote:
> On 05/20/2014 04:55 AM, Stephen Warren wrote:
>> On 05/18/2014 08:54 PM, FanWu wrote:
>>> On 05/17/2014 03:53 AM, Stephen Warren wrote:
>>>> On 05/16/2014 10:21 AM, Linus Walleij wrote:
>>>>> On Wed, May 14, 2014 at 4:01 AM,  <fwu@...vell.com> wrote:
>>>>>
>>>>>> From: Fan Wu <fwu@...vell.com>
>>>>>>
>>>>>> The patch added params in disable_setting to differ the two possible
>>>>>> usage,
>>>>>> 1.Only want to disable the pin setting in SW aspect, param can be
>>>>>> set to "0"
>>>>>> 2.Want to disable the pin setting in both HW and SW aspect, param
>>>>>> can be set to "1";
>>>>>>
>>>>>> The reason why to do this is that:
>>>>>> To avoid duplicated enable_setting operation without disabling
>>>>>> operation which will
>>>>>> let Pin's desc->mux_usecount keep being added.
>>>>>>
>>>>>> In the following case, the issue can be reproduced:
>>>>>> 1)There is a driver need to switch Pin state dynamicly, E.g. b/t
>>>>>> "sleep" and
>>>>>> "default" state
>>>>>> 2)The Pin setting configuration in the two state is same, like the
>>>>>> following one:
>>>>>> component a {
>>>>>>           pinctrl-names = "default", "sleep";
>>>>>>           pinctrl-0 = <&a_grp_setting &c_grp_setting>;
>>>>>>           pinctrl-1 = <&b_grp_setting &c_grp_setting>;
>>>>>> }
>>>>>> The "c_grp_setting" config node is totaly same, maybe like following
>>>>>> one:
>>>>>
>>>>> Hm this is a quite interesting thing if we can get it in place, but
>>>>> I need Stephen's consent, also Tony should have a look at this as
>>>>> I know he's had the same problem as you in pinctrl-single.
>>>>
>>>> I only briefly looked at the patch, but it probably solves/hides the
>>>> immediate problem.
>>>>
>>>> However, rather than doing this, why not just remove
>>>> pinmux_disable_setting() completely. It doesn't make sense to
>>>> "disable a
>>>> mux selection" (some value is always selected in the mux register
>>>> field)
>>>> any more than it does to "disable a drive strength selection". We don't
>>>> have a pinconf_disable_setting(), and couldn't really add one if we
>>>> wanted. For consistency, let's just remove pinmux_disable_setting(). Do
>>>> you agree?
>>>>
>>>
>>> Dear, Stephen and Guys,
>>>
>>> Sorry for late due to some personal affairs in Weekend time.
>>>
>>> I don't think it is a proper way to remove pinmux_disable_setting
>>> directly without changing any other code, like no change on the code in
>>> pinmux_enable_setting.
>>>
>>> Talking about the pinmux_disable_operation, in SW aspect, we also need
>>> to consider the "pinmux_enable_setting" operation.
>>> For the "pinmux_enable_setting" operation, there is some SW level code
>>> logic, like pin_request.
>>> Do you think it is a acceptable way to remove the SW level code logic
>>> from the "pinmux_enable_setting" path, because there will be no
>>> corresponding operation in reverse order in pinmux_disable_setting after
>>> applying our possible change?
>>
>> No, I don't think we should remove the SW aspects of
>> pinmux_enable_setting(). The pinctrl core currently tracks which pinctrl
>> state "owns" each pingroup's mux, so that different pinctrl states can't
>> both attempt to configure a pingroup's mux setting. We need to keep all
>> the SW aspects of mux enable/disable. All I'm proposing removing is the
>> HW-programming parts of pinmux_disable_setting().
>>
>>> At least, I think this way may be a considerable change in Pinmux
>>> framework, right?
>>
>> Yes, removing all of pinmux_en/disable_setting would be a considerable
>> and likely inappropriate change.
>>
>>> Talking about HW aspect,
>>> I think the solution you mentioned is indeed a good way to solve the
>>> problem for some HW vendor's SoC chip, but may be not that intact
>>> solution.
>>>
>>> In my understanding, the pinmux operation, like enabling and disabling,
>>> is to change pin's(pins') multi-function from funcion_M to function_N.
>>> And, the "pinconf" enabling function is used to change the attributes of
>>> the pin, like Pull_Up/Down, DriveStrength(Low/Medium/Fast) and etc.
>>>
>>> The pinmux disabling operation will be called in the following case in
>>> current pinmux framework:
>>> 1. when pin(s) is/are freed or error handler when configure it(them) and
>>> finally the pin will be changed to a disabled/safe state if defined by
>>> vendor.
>>> 2. in the pinctrl_select_state function
>>>
>>> The item 2# is just the thing we talked about in this loop and we reach
>>> agreement that the item 2# is not useful.
>>>
>>> I think the item 1# is still useful for some vendor if they defined the
>>> disabled/safe multi-function for a pin. They may expect the pin is
>>> changed to the disabled/safe state for saving power or some security
>>> reason.
>>
>> The only time item #1 above would happen is an error case. If there's an
>> error, there shouldn't be any expectation for the specific state of the
>> pinmux. If this intermediate state is illegal, then that's a problem in
>> an of itself; the HW is going to be in that state for some (admittedly
>> small) amount of time while the pinmux is being programmed, error or no
>> error, hence all the intermediate states had better be legal. I think
>> it's fine if the HW programming is simply left in whatever partial state
>> the code managed to get to. It's quite unlikely there's any "safe" state
>> that's /meaningfully/ better for a pin to be in once an error is
>> detected.
>>
>>> Thus, I think we should keep the disable_pinmux_setting in pinmux code.
>>>
>>> Do you think what I mentioned is an acceptable and not that aggressive
>>> solution?
>>
>> Not really.
>>
>>> Please correct me if anything wrong.
>>>
>>>
>>>
>>> For another topics:
>>> 1. There is no disable_pinconf: I think this is a issue. When the pin's
>>> mux setting is changed, the pinconf setting should also be changed, at
>>> least, the pinmux code here should offer the user a chance(interface) to
>>> decide whether to change the pinconf setting. Thus, we may need to add
>>> pinconf disable function.
>>
>> pinctrl already allows any config options to be changed along with the
>> mux option.
>>
>> The only reason any mux or config option is ever changed is in response
>> to selecting a new pinctrl state. Hence, I don't think you ever want to
>> "disable" either a mux or config option. Rather, you simply want to
>> "enable" or "select" or "program" the mux/config options in the new
>> state. Any mux/config option that needs to differ between states should
>> simply be listed in all the states, so that when the state is entered,
>> the appropriate HW programming is performed.
>>
>>> 2. If the vendor use pinctrl-single driver, the
>>> "pinctrl-single,function-off" implementation is not useful in practical
>>> usage. The "pinctrl-single,function-off" is parsed when pinctrl-single
>>> driver probe phase and the instance setting of
>>> "pinctrl-single,function-off" will be used for all pins setting.
>>> Practically, I think different pins may have different disabled/safe.
>>
>> I'm not sure what you're asking here.
>>
> 
> Dear Stephen,
> 
> I think we have reached the agreement that the HW operation should be
> avoided in disable_pinmux_setting. Just a little difference, I insist
> that the HW operation should only should be removed sometimes not always.
> 
> I think the disable_pinmux_setting is not only called by the error
> handler but also the
> "pinctrl_put=>pinctrl_release=>...=>"pinctrl_free_setting" call stack
> when there is no any alive user to use this pin.
> In this case,
> the pinmux_disable_setting will try to put the pin to a fixed and final
> state, not intermediate state, and should offer the vendor's driver an
> interface to place the pin to the unused(disabled/safe) state(HW aspect).
> 
> Thus, I think we should remove HW operation in pinmux_disabl_setting
> only for some cases, just same as what I mentioned in my patch.
> 
> Did I got anything wrong ?

Like I said, I think there's really not much point in doing that, and
it'll just make the code more complicated than it needs to be.

However, if LinusW is OK taking that patch, I don't have any problem
with it; that change won't cause any problems on any HW platform I have.
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