[PATCH v6 4/7] pinctrl: add optional .release_mux() callback

[Frank Li <Frank.Li@nxp.com>]

Add an optional .release_mux() callback to struct pinmux_ops.

Some drivers acquire additional resources in .set_mux(), such as software
locks. These resources may need to be released when the mux function is no
longer active. Introducing a dedicated .release_mux() callback allows
drivers to clean up such resources.

The callback is optional and does not affect existing drivers.

Commit 2243a87d90b42 ("pinctrl: avoid duplicated calling
enable_pinmux_setting for a pin") removed the .disable() callback
to resolve two issues:

  1. desc->mux_usecount increasing monotonically
  2. Hardware glitches caused by repeated .disable()/.enable() calls

Adding .release_mux() does not reintroduce those problems. The callback is
intended only for releasing driver-side resources (e.g. locks) and must not
modify hardware registers.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
change in v4
- none

change in v3
- Add judgement about 2243a87d90b42 ("pinctrl: avoid duplicated calling
enable_pinmux_setting for a pin") in commit message.
---
 drivers/pinctrl/pinmux.c       | 5 +++++
 include/linux/pinctrl/pinmux.h | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/pinctrl/pinmux.c b/drivers/pinctrl/pinmux.c
index 3a8dd184ba3d670e01a890427e19af59b65eb813..c705bc182266c596c4e6c820f5e3ffcadbbb2838 100644
--- a/drivers/pinctrl/pinmux.c
+++ b/drivers/pinctrl/pinmux.c
@@ -517,6 +517,7 @@ void pinmux_disable_setting(const struct pinctrl_setting *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 = 0;
 	const unsigned int *pins = NULL;
 	unsigned int num_pins = 0;
@@ -563,6 +564,10 @@ void pinmux_disable_setting(const struct pinctrl_setting *setting)
 				 pins[i], desc->name, gname);
 		}
 	}
+
+	if (ops->release_mux)
+		ops->release_mux(pctldev, setting->data.mux.func,
+				 setting->data.mux.group);
 }
 
 #ifdef CONFIG_DEBUG_FS
diff --git a/include/linux/pinctrl/pinmux.h b/include/linux/pinctrl/pinmux.h
index 094bbe2fd6fd5ea3c5fdf5b6d6d9a7639700b50b..77664937eeb273eef440988c4cf833dbc6f10758 100644
--- a/include/linux/pinctrl/pinmux.h
+++ b/include/linux/pinctrl/pinmux.h
@@ -51,6 +51,8 @@ struct pinctrl_gpio_range;
  *	are handled by the pinmux subsystem. The @func_selector selects a
  *	certain function whereas @group_selector selects a certain set of pins
  *	to be used. On simple controllers the latter argument may be ignored
+ * @release_mux: Release software resources acquired by @set_mux. This callback
+ *	must not change hardware state to avoid glitches when switching mux.
  * @gpio_request_enable: requests and enables GPIO on a certain pin.
  *	Implement this only if you can mux every pin individually as GPIO. The
  *	affected GPIO range is passed along with an offset(pin number) into that
@@ -80,6 +82,9 @@ struct pinmux_ops {
 				  unsigned int selector);
 	int (*set_mux) (struct pinctrl_dev *pctldev, unsigned int func_selector,
 			unsigned int group_selector);
+	void (*release_mux) (struct pinctrl_dev *pctldev,
+			     unsigned int func_selector,
+			     unsigned int group_selector);
 	int (*gpio_request_enable) (struct pinctrl_dev *pctldev,
 				    struct pinctrl_gpio_range *range,
 				    unsigned int offset);

-- 
2.43.0