linux-kernel - Re: [Pinctrl] A suggestion to avoid duplicated enabling operation on a pin's setting

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Date:	Tue, 13 May 2014 09:42:32 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	FanWu <fwu@...vell.com>
CC:	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"swarren@...dia.com" <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: [Pinctrl] A suggestion to avoid duplicated enabling operation
 on a pin's setting

On 05/12/2014 11:53 PM, FanWu wrote:
...
> About the glitch I mentioned before, I want to make myself clear.
> If there is a case like the following one:
> pinctrl-0 = <&a_grp_settingA>;
> pinctrl-1 = <&a_grp_settingB>;
> "a_grp_settingA" and "a_grp_settingB" are used to described the same
> Pin's different mux and function configuration
> In my understanding,
> When there is a need to switch Pin group state, the current code will
> disable "a_grp_settingA" first ahead of enabling "a_grp_settingB", right ?

Yes.

> Do you mean the case I mentioned will not be a glitch ?

I guess you're talking about that:

>> In the original code, the Pin setting will be changed to the
>> disabled/safe state when Pin state is switched if the old setting is not
>> existed in new state rather than directly switched to the new Pin
>> setting. Also a possible glitch?

Yes, in this case, there is no glitch. However, there is certainly a
change in HW configuration. A glitch is a temporary short-term
accidental change in output value or configuration. In the case quoted
immediately above, the change is permanent - at least until some other
state is activated later. Hence, there is no glitch. However, there
certainly is a change in HW configuration, and that could be just as
problematic, depending on the HW and exact pin configuration.
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