Date:	Mon, 26 May 2014 10:52:14 +0800
From:	FanWu <fwu@...vell.com>
To:	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"tony@...mide.com" <tony@...mide.com>
CC:	"fwu@...vell.com" <fwu@...vell.com>,
	"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>, <wwang27@...vell.com>,
	<jxiang@...vell.com>
Subject: Re: [PATCH v3] pinctrl: to avoid duplicated calling enable_pinmux_setting
 for a pin

On 05/26/2014 10:43 AM, fwu@...vell.com wrote:
> From: Fan Wu <fwu@...vell.com>
>
> What the patch did:
> 1.To call pinmux_disable_setting ahead of pinmux_enable_setting in each time of
>    calling pinctrl_select_state
> 2.Remove the HW disable operation in in pinmux_disable_setting function.
>
> The reason why to do this is that:
> 1.To avoid duplicated calling enable_setting operation without disabling
>    operation which will let Pin's desc->mux_usecount keep being added.
> 2.The HW pin disable operation is not useful for most of the vendors' platform.
>    And this can be used to avoid the HW glitch after using the item 1#
>    modification.
>
> 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 DTS node may be 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:
> c_grp_setting: c_grp_setting {
> 	pinctrl-single,pins = <GPIO48 AF6>;
> 	MFP_DEFAULT;
> }
> 3)When switching the Pin state in the following official Pinctrl sequence:
> 	pin = pinctrl_get();
> 	state = pinctrl_lookup_state(wanted_state);
> 	pinctrl_select_state(state);
> 	pinctrl_put();
>
> Test Result:
> 1)The switch is completed as expectation, that is: component's
> Pins configuration are changed according to the description in the
> "wanted_state" group setting
> 2)The "desc->mux_usecount" of corresponding Pins in "c_group" is added without being
> decreased, because the "desc" is for each physical pin while the "setting" is
> for each setting node in the DTS.
> Thus, if the "c_grp_setting" in pinctrl-0 is not disabled ahead of enabling
> "c_grp_setting" in pinctrl-1, the desc->mux_usecount will be kept added without
> any chance to be decreased.
>
> According to the comments in the original code, only the setting, in old state
> but not in new state, will be "disable"(calling pinmux_disable_setting), which
> is correct logic but not intact. We still need consider case that the setting
> is in both old state and new state.
> We can do this in the following two ways:
> 1) Avoid "enable"(calling pinmux_enable_setting) the Same Pins setting repeatedly.
> 2) "Disable"(calling pinmux_disable_setting) the "Same Pins setting", actually
> two setting instance, ahead of enabling them.
>
> Analysis:
> 1.The solution 2# is better because it can avoid too much iteration.
> 2.If we disable all of the setting in the old state and one/ones of the setting(s) is/are
> existed in the new state, the Pin's mux function change may happen when
> some SoC vendors defined the "pinctrl-single,function-off" in their DTS file.
> old_setting=>disabled_setting=>new_setting.
> 3.In the pinmux framework, when Pin state is switched, the setting in the old state should be
> marked as "disabled".
>
> Conclusion:
> 1.To Remove the HW disabling operation to above the glitch mentioned above.
> 2.Handle the issue mentioned above by disabling all of the settings in old
> state and then enable the all of the settings in new state.
>
> Signed-off-by: Fan Wu <fwu@...vell.com>
> Signed-off-by: Stephen Warren <swarren@...dia.com>
> ---
>   drivers/pinctrl/core.c   |   24 +++++-------------------
>   drivers/pinctrl/pinmux.c |    4 ----
>   2 files changed, 5 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/pinctrl/core.c b/drivers/pinctrl/core.c
> index c0fe609..4445a67 100644
> --- a/drivers/pinctrl/core.c
> +++ b/drivers/pinctrl/core.c
> @@ -989,29 +989,15 @@ int pinctrl_select_state(struct pinctrl *p, struct pinctrl_state *state)
>
>   	if (p->state) {
>   		/*
> -		 * The set of groups with a mux configuration in the old state
> -		 * may not be identical to the set of groups with a mux setting
> -		 * in the new state. While this might be unusual, it's entirely
> -		 * possible for the "user"-supplied mapping table to be written
> -		 * that way. For each group that was configured in the old state
> -		 * but not in the new state, this code puts that group into a
> -		 * safe/disabled state.
> +		 * For each pinmux setting in the old state, forget SW's record
> +		 * of mux owner for that pingroup. Any pingroups which are
> +		 * still owned by the new state will be re-acquired by the call
> +		 * to pinmux_enable_setting() in the loop below.
>   		 */
>   		list_for_each_entry(setting, &p->state->settings, node) {
> -			bool found = false;
>   			if (setting->type != PIN_MAP_TYPE_MUX_GROUP)
>   				continue;
> -			list_for_each_entry(setting2, &state->settings, node) {
> -				if (setting2->type != PIN_MAP_TYPE_MUX_GROUP)
> -					continue;
> -				if (setting2->data.mux.group ==
> -						setting->data.mux.group) {
> -					found = true;
> -					break;
> -				}
> -			}
> -			if (!found)
> -				pinmux_disable_setting(setting);
> +			pinmux_disable_setting(setting);
>   		}
>   	}
>
> diff --git a/drivers/pinctrl/pinmux.c b/drivers/pinctrl/pinmux.c
> index 9248ce4..c2c4aff 100644
> --- a/drivers/pinctrl/pinmux.c
> +++ b/drivers/pinctrl/pinmux.c
> @@ -469,7 +469,6 @@ void pinmux_disable_setting(struct pinctrl_setting const *setting)
>   {
>   	struct pinctrl_dev *pctldev = setting->pctldev;
>   	const struct pinctrl_ops *pctlops = pctldev->desc->pctlops;
> -	const struct pinmux_ops *ops = pctldev->desc->pmxops;
>   	int ret;
>   	const unsigned *pins;
>   	unsigned num_pins;
> @@ -515,9 +514,6 @@ void pinmux_disable_setting(struct pinctrl_setting const *setting)
>   				 pins[i], desc->name, gname);
>   		}
>   	}
> -
> -	if (ops->disable)
> -		ops->disable(pctldev, setting->data.mux.func, setting->data.mux.group);
>   }
>
>   #ifdef CONFIG_DEBUG_FS
>


Dear Stephen,

Great thanks for your suggestion about the inline comments in the patch.
I have updated the part you mentioned and the patch title.
Please help to review again.

Great to see that we almost get the goal of the long term discussion! :)

After this patch is acknowledged by you Guys, I will submit the 
following two patches for you to review:
1.to remove the ops->disable registration in pinctrl-single
2.to remove the ops->disable function phandle in pinmux struct.

Great thanks for this !

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