Message-ID: <537AC661.7010400@marvell.com>
Date:	Tue, 20 May 2014 11:05:05 +0800
From:	FanWu <fwu@...vell.com>
To:	Stephen Warren <swarren@...dotorg.org>
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 05/20/2014 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 ?

Great thanks !

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