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pinctrl: avoid duplicated calling enable_pinmux_setting for a pin
What the patch does:
1. Call pinmux_disable_setting ahead of pinmux_enable_setting
each time pinctrl_select_state is called
2. Remove the HW disable operation in pinmux_disable_setting function.
3. Remove the disable ops in struct pinmux_ops
4. Remove all the disable ops users in current code base.
Notes:
1. Great thanks for the suggestion from Linus, Tony Lindgren and
Stephen Warren and Everyone that shared comments on this patch.
2. The patch also includes comment fixes from Stephen Warren.
The reason why we do this:
1. To avoid duplicated calling of the enable_setting operation
without disabling operation inbetween which will let the pin
descriptor desc->mux_usecount increase monotonously.
2. The HW pin disable operation is not useful for any of the
existing platforms.
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 that need to switch pin state dynamically,
e.g. between "sleep" and "default" state
2. The pin setting configuration in a DTS node may be like this:
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 totally identical, maybe like
following one:
c_grp_setting: c_grp_setting {
pinctrl-single,pins = <GPIO48 AF6>;
}
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 expected, that is: the device's
pin configuration is changed according to the description in the
"wanted_state" group setting
2. The "desc->mux_usecount" of the corresponding pins in "c_group"
is increased 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 keep increasing 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 "disabled" (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 to "enable"(calling pinmux_enable_setting) the "same pin
setting" repeatedly
2. "Disable"(calling pinmux_disable_setting) the "same pin setting",
actually two setting instances, 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 settings in the old state and one of
the setting(s) exist in the new state, the pins 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 a 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@marvell.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>