• Fan Wu's avatar
    pinctrl: avoid duplicated calling enable_pinmux_setting for a pin · 2243a87d
    Fan Wu authored
    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: default avatarFan Wu <fwu@marvell.com>
    Acked-by: default avatarStephen Warren <swarren@nvidia.com>
    Acked-by: default avatarPatrice Chotard <patrice.chotard@st.com>
    Acked-by: default avatarHeiko Stuebner <heiko@sntech.de>
    Acked-by: default avatarMaxime Coquelin <maxime.coquelin@st.com>
    Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
    2243a87d
pinctrl-bcm2835.c 27.5 KB