[PATCH v8 0/7] mmc: host: renesas_sdhi_core: support configuring an optional sdio mux

[PATCH v8 0/7] mmc: host: renesas_sdhi_core: support configuring an optional sdio mux

[Josua Mayer]

Some Renesas SoC based boards mux SD and eMMC on a single sdio
controller, exposing user control by dip switch and software control by
gpio.

Purpose is to simplify development and provisioning by selecting boot
media at power-on, and again before starting linux.

Add binding and driver support for linking a (gpio) mux to renesas sdio
controller.

Introduce generic helper functions for getting managed and selected
mux-state objects, and switch i2c-omap and phy-can-transceiver drivers.

Signed-off-by: Josua Mayer <josua@solid-run.com>
---
Changes in v8:
- Add defensive null checks for all non-optional calls to internal
  mux_get function.
- Document NULL return value on applicable functions.
- Avoid IS_ERR_OR_NULL and ERR_PTR(0) to disarm smatch errors.
- Link to v7: https://lore.kernel.org/r/20260128-rz-sdio-mux-v7-0-92ebb6da0df8@solid-run.com

Changes in v7:
- picked up reviewed-tags
- fix Kconfig change to add the missing prompt for CONFIG_MULTIPLEXER,
  and enable it by default when COMPILE_TEST is set.
  (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
- fix another kernel build robot warning: undocumented C struct member
- Link to v6: https://lore.kernel.org/r/20260121-rz-sdio-mux-v6-0-38aa39527928@solid-run.com

Changes in v6:
- replaced /* with /** for devm_mux_state_state function description.
- collected review tags.
- fixed checkpatch warnings (space-before-tab, void-return).
  (Reported-by: Geert Uytterhoeven)
- fixed use-after-free in mux core mux_get function.
  (Reported-by: Geert Uytterhoeven)
- fix mux helper error path uninitialised return code variable.
  (Reported-by: kernel test robot <lkp@intel.com>)
- Link to v5: https://lore.kernel.org/r/20260118-rz-sdio-mux-v5-0-3c37e8872683@solid-run.com

Changes in v5:
- implemented automatic mux deselect for devm_*_selected.
  (Reported-by: Wolfram Sang <wsa+renesas@sang-engineering.com>)
- because of semantic changes I dropped reviewed and acks from omap-i2c
  patch (Andreas Kemnade / Wolfram Sang).
- fix invalid return value in void function for mux helper stubs
  (Reported-by: kernel test robot <lkp@intel.com>)
- Link to v4: https://lore.kernel.org/r/20251229-rz-sdio-mux-v4-0-a023e55758fe@solid-run.com

Changes in v4:
- added MULTIPLEXER Kconfig help text.
- removed "select MULTIPLEXER" from renesas sdhi Kconfig, as it is
  not required for all devices using this driver.
- added stubs for all symbols exported by mux core.
  (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
- refactored mux core logic to silence ENOENT errors only on optional
  code paths, keeping error printing unchanged otherwise.
  (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
- picked up various reviewed- and acked-by tags
- Link to v3: https://lore.kernel.org/r/20251210-rz-sdio-mux-v3-0-ca628db56d60@solid-run.com

Changes in v3:
- updated omap-i2c and phy-can-transceiver to use new helpers.
- created generic helper functions for getting managed optional mux-state.
  (Reported-by: Rob Herring <robh@kernel.org>)
- picked up binding ack by Rob Herring.
- replaced use of "SDIO" with "SD/SDIO/eMMC" in binding document and
  commit descriptions.
  (Reported-by: Ulf Hansson <ulf.hansson@linaro.org>)
- Link to v2: https://lore.kernel.org/r/20251201-rz-sdio-mux-v2-0-bcb581b88dd7@solid-run.com

Changes in v2:
- dropped mux-controller node from dt binding example
  (Reported-by: Conor Dooley <conor@kernel.org>
   Reported-by: Krzysztof Kozlowski <krzk@kernel.org>)
- Link to v1: https://lore.kernel.org/r/20251128-rz-sdio-mux-v1-0-1ede318d160f@solid-run.com

---
Josua Mayer (7):
      phy: can-transceiver: rename temporary helper function to avoid conflict
      mux: Add helper functions for getting optional and selected mux-state
      mux: add help text for MULTIPLEXER config option
      phy: can-transceiver: drop temporary helper getting optional mux-state
      i2c: omap: switch to new generic helper for getting selected mux-state
      dt-bindings: mmc: renesas,sdhi: Add mux-states property
      mmc: host: renesas_sdhi_core: support selecting an optional mux

 .../devicetree/bindings/mmc/renesas,sdhi.yaml      |   6 +
 drivers/i2c/busses/i2c-omap.c                      |  24 +--
 drivers/mmc/host/renesas_sdhi_core.c               |   6 +
 drivers/mux/Kconfig                                |   8 +-
 drivers/mux/core.c                                 | 205 +++++++++++++++++----
 drivers/phy/phy-can-transceiver.c                  |  10 -
 include/linux/mux/consumer.h                       | 108 ++++++++++-
 7 files changed, 302 insertions(+), 65 deletions(-)
---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251128-rz-sdio-mux-acc5137f1618

Best regards,
-- 
Josua Mayer <josua@solid-run.com>

[PATCH v8 1/7] phy: can-transceiver: rename temporary helper function to avoid conflict

[Josua Mayer]

Rename the temporary devm_mux_state_get_optional function to avoid
conflict with upcoming implementation in multiplexer subsystem.

Acked-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/phy/phy-can-transceiver.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/phy/phy-can-transceiver.c b/drivers/phy/phy-can-transceiver.c
index 330356706ad7..81591d247128 100644
--- a/drivers/phy/phy-can-transceiver.c
+++ b/drivers/phy/phy-can-transceiver.c
@@ -128,7 +128,7 @@ MODULE_DEVICE_TABLE(of, can_transceiver_phy_ids);
 
 /* Temporary wrapper until the multiplexer subsystem supports optional muxes */
 static inline struct mux_state *
-devm_mux_state_get_optional(struct device *dev, const char *mux_name)
+temp_devm_mux_state_get_optional(struct device *dev, const char *mux_name)
 {
 	if (!of_property_present(dev->of_node, "mux-states"))
 		return NULL;
@@ -183,7 +183,7 @@ static int can_transceiver_phy_probe(struct platform_device *pdev)
 	priv->num_ch = num_ch;
 	platform_set_drvdata(pdev, priv);
 
-	mux_state = devm_mux_state_get_optional(dev, NULL);
+	mux_state = temp_devm_mux_state_get_optional(dev, NULL);
 	if (IS_ERR(mux_state))
 		return PTR_ERR(mux_state);
 

-- 
2.43.0

[PATCH v8 2/7] mux: Add helper functions for getting optional and selected mux-state

[Josua Mayer]

In-tree phy-can-transceiver driver has already implemented a local
version of devm_mux_state_get_optional.

The omap-i2c driver gets and selects an optional mux in its probe
function without using any helper.

Add new helper functions covering both aforementioned use-cases:

- mux_control_get_optional:
  Get a mux-control if specified in dt, return NULL otherwise.
- devm_mux_state_get_optional:
  Get a mux-state if specified in dt, return NULL otherwise.
- devm_mux_state_get_selected:
  Get and select a mux-state specified in dt, return error otherwise.
- devm_mux_state_get_optional_selected:
  Get and select a mux-state if specified in dt, return error or NULL.

Existing mux_get helper function is changed to take an extra argument
indicating whether the mux is optional.
In this case no error is printed, and NULL returned in case of ENOENT.

Calling code is adapted to handle NULL return case, and to pass optional
argument as required.

To support automatic deselect for _selected helper, a new structure is
created storing an exit pointer similar to clock core which is called on
release.

To facilitate code sharing between optional/mandatory/selected helpers,
a new internal helper function is added to handle quiet (optional) and
verbose (mandatory) errors, as well as storing the correct callback for
devm release: __devm_mux_state_get

Due to this structure devm_mux_state_get_*_selected can no longer print
a useful error message when select fails. Instead callers should print
errors where needed.

Commit e153fdea9db04 ("phy: can-transceiver: Re-instate "mux-states"
property presence check") noted that "mux_get() always prints an error
message in case of an error, including when the property is not present,
confusing the user."

The first error message covers the case that a mux name is not matched
in dt. The second error message is based on of_parse_phandle_with_args
return value.

In optional case no error is printed and NULL is returned.
This ensures that the new helper functions will not confuse the user
either.

With the addition of optional helper functions it became clear that
drivers should compile and link even if CONFIG_MULTIPLEXER was not enabled.
Add stubs for all symbols exported by mux core.

Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/mux/core.c           | 205 ++++++++++++++++++++++++++++++++++++-------
 include/linux/mux/consumer.h | 108 ++++++++++++++++++++++-
 2 files changed, 278 insertions(+), 35 deletions(-)

diff --git a/drivers/mux/core.c b/drivers/mux/core.c
index a3840fe0995f..2e8295e3aabe 100644
--- a/drivers/mux/core.c
+++ b/drivers/mux/core.c
@@ -46,6 +46,16 @@ static const struct class mux_class = {
 	.name = "mux",
 };
 
+/**
+ * struct devm_mux_state_state -	Tracks managed resources for mux-state objects.
+ * @mstate:				Pointer to a mux state.
+ * @exit:				An optional callback to execute before free.
+ */
+struct devm_mux_state_state {
+	struct mux_state *mstate;
+	int (*exit)(struct mux_state *mstate);
+};
+
 static DEFINE_IDA(mux_ida);
 
 static int __init mux_init(void)
@@ -516,17 +526,19 @@ static struct mux_chip *of_find_mux_chip_by_node(struct device_node *np)
 	return dev ? to_mux_chip(dev) : NULL;
 }
 
-/*
+/**
  * mux_get() - Get the mux-control for a device.
  * @dev: The device that needs a mux-control.
  * @mux_name: The name identifying the mux-control.
  * @state: Pointer to where the requested state is returned, or NULL when
  *         the required multiplexer states are handled by other means.
+ * @optional: Whether to return NULL and silence errors when mux doesn't exist.
  *
- * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
+ * Return: Pointer to the mux-control on success, an ERR_PTR with a negative errno on error,
+ * or NULL if optional is true and mux doesn't exist.
  */
 static struct mux_control *mux_get(struct device *dev, const char *mux_name,
-				   unsigned int *state)
+				   unsigned int *state, bool optional)
 {
 	struct device_node *np = dev->of_node;
 	struct of_phandle_args args;
@@ -542,7 +554,9 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
 		else
 			index = of_property_match_string(np, "mux-control-names",
 							 mux_name);
-		if (index < 0) {
+		if (index < 0 && optional) {
+			return NULL;
+		} else if (index < 0) {
 			dev_err(dev, "mux controller '%s' not found\n",
 				mux_name);
 			return ERR_PTR(index);
@@ -558,8 +572,12 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
 						 "mux-controls", "#mux-control-cells",
 						 index, &args);
 	if (ret) {
+		if (optional && ret == -ENOENT)
+			return NULL;
+
 		dev_err(dev, "%pOF: failed to get mux-%s %s(%i)\n",
-			np, state ? "state" : "control", mux_name ?: "", index);
+			np, state ? "state" : "control",
+			mux_name ?: "", index);
 		return ERR_PTR(ret);
 	}
 
@@ -617,10 +635,28 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
  */
 struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
 {
-	return mux_get(dev, mux_name, NULL);
+	struct mux_control *mux = mux_get(dev, mux_name, NULL, false);
+
+	if (!mux)
+		return ERR_PTR(-ENOENT);
+
+	return mux;
 }
 EXPORT_SYMBOL_GPL(mux_control_get);
 
+/**
+ * mux_control_get_optional() - Get the optional mux-control for a device.
+ * @dev: The device that needs a mux-control.
+ * @mux_name: The name identifying the mux-control.
+ *
+ * Return: A pointer to the mux-control, an ERR_PTR with a negative errno.
+ */
+struct mux_control *mux_control_get_optional(struct device *dev, const char *mux_name)
+{
+	return mux_get(dev, mux_name, NULL, true);
+}
+EXPORT_SYMBOL_GPL(mux_control_get_optional);
+
 /**
  * mux_control_put() - Put away the mux-control for good.
  * @mux: The mux-control to put away.
@@ -657,10 +693,13 @@ struct mux_control *devm_mux_control_get(struct device *dev,
 	if (!ptr)
 		return ERR_PTR(-ENOMEM);
 
-	mux = mux_control_get(dev, mux_name);
+	mux = mux_get(dev, mux_name, NULL, false);
 	if (IS_ERR(mux)) {
 		devres_free(ptr);
 		return mux;
+	} else if (!mux) {
+		devres_free(ptr);
+		return ERR_PTR(-ENOENT);
 	}
 
 	*ptr = mux;
@@ -670,14 +709,16 @@ struct mux_control *devm_mux_control_get(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(devm_mux_control_get);
 
-/*
+/**
  * mux_state_get() - Get the mux-state for a device.
  * @dev: The device that needs a mux-state.
  * @mux_name: The name identifying the mux-state.
+ * @optional: Whether to return NULL and silence errors when mux doesn't exist.
  *
- * Return: A pointer to the mux-state, or an ERR_PTR with a negative errno.
+ * Return: Pointer to the mux-state on success, an ERR_PTR with a negative errno on error,
+ * or NULL if optional is true and mux doesn't exist.
  */
-static struct mux_state *mux_state_get(struct device *dev, const char *mux_name)
+static struct mux_state *mux_state_get(struct device *dev, const char *mux_name, bool optional)
 {
 	struct mux_state *mstate;
 
@@ -685,12 +726,16 @@ static struct mux_state *mux_state_get(struct device *dev, const char *mux_name)
 	if (!mstate)
 		return ERR_PTR(-ENOMEM);
 
-	mstate->mux = mux_get(dev, mux_name, &mstate->state);
+	mstate->mux = mux_get(dev, mux_name, &mstate->state, optional);
 	if (IS_ERR(mstate->mux)) {
-		int err = PTR_ERR(mstate->mux);
-
 		kfree(mstate);
-		return ERR_PTR(err);
+		return ERR_CAST(mstate->mux);
+	} else if (optional && !mstate->mux) {
+		kfree(mstate);
+		return NULL;
+	} else if (!mstate->mux) {
+		kfree(mstate);
+		return ERR_PTR(-ENOENT);
 	}
 
 	return mstate;
@@ -710,9 +755,66 @@ static void mux_state_put(struct mux_state *mstate)
 
 static void devm_mux_state_release(struct device *dev, void *res)
 {
-	struct mux_state *mstate = *(struct mux_state **)res;
+	struct devm_mux_state_state *devm_state = res;
 
+	if (devm_state->exit)
+		devm_state->exit(devm_state->mstate);
+
+	mux_state_put(devm_state->mstate);
+}
+
+/**
+ * __devm_mux_state_get() - Get the optional mux-state for a device,
+ *			    with resource management.
+ * @dev: The device that needs a mux-state.
+ * @mux_name: The name identifying the mux-state.
+ * @optional: Whether to return NULL and silence errors when mux doesn't exist.
+ * @init: Optional function pointer for mux-state object initialisation.
+ * @exit: Optional function pointer for mux-state object cleanup on release.
+ *
+ * Return: Pointer to the mux-state on success, an ERR_PTR with a negative errno on error,
+ * or NULL if optional is true and mux doesn't exist.
+ */
+static struct mux_state *__devm_mux_state_get(struct device *dev, const char *mux_name,
+					      bool optional,
+					      int (*init)(struct mux_state *mstate),
+					      int (*exit)(struct mux_state *mstate))
+{
+	struct devm_mux_state_state *devm_state;
+	struct mux_state *mstate;
+	int ret;
+
+	mstate = mux_state_get(dev, mux_name, optional);
+	if (IS_ERR(mstate))
+		return ERR_CAST(mstate);
+	else if (optional && !mstate)
+		return NULL;
+	else if (!mstate)
+		return ERR_PTR(-ENOENT);
+
+	devm_state = devres_alloc(devm_mux_state_release, sizeof(*devm_state), GFP_KERNEL);
+	if (!devm_state) {
+		ret = -ENOMEM;
+		goto err_devres_alloc;
+	}
+
+	if (init) {
+		ret = init(mstate);
+		if (ret)
+			goto err_mux_state_init;
+	}
+
+	devm_state->mstate = mstate;
+	devm_state->exit = exit;
+	devres_add(dev, devm_state);
+
+	return mstate;
+
+err_mux_state_init:
+	devres_free(devm_state);
+err_devres_alloc:
 	mux_state_put(mstate);
+	return ERR_PTR(ret);
 }
 
 /**
@@ -722,28 +824,69 @@ static void devm_mux_state_release(struct device *dev, void *res)
  * @mux_name: The name identifying the mux-control.
  *
  * Return: Pointer to the mux-state, or an ERR_PTR with a negative errno.
+ *
+ * The mux-state will automatically be freed on release.
  */
-struct mux_state *devm_mux_state_get(struct device *dev,
-				     const char *mux_name)
+struct mux_state *devm_mux_state_get(struct device *dev, const char *mux_name)
 {
-	struct mux_state **ptr, *mstate;
-
-	ptr = devres_alloc(devm_mux_state_release, sizeof(*ptr), GFP_KERNEL);
-	if (!ptr)
-		return ERR_PTR(-ENOMEM);
+	return __devm_mux_state_get(dev, mux_name, false, NULL, NULL);
+}
+EXPORT_SYMBOL_GPL(devm_mux_state_get);
 
-	mstate = mux_state_get(dev, mux_name);
-	if (IS_ERR(mstate)) {
-		devres_free(ptr);
-		return mstate;
-	}
+/**
+ * devm_mux_state_get_optional() - Get the optional mux-state for a device,
+ *				   with resource management.
+ * @dev: The device that needs a mux-state.
+ * @mux_name: The name identifying the mux-state.
+ *
+ * Return: Pointer to the mux-state on success, an ERR_PTR with a negative errno on error,
+ * or NULL if mux doesn't exist.
+ *
+ * The mux-state will automatically be freed on release.
+ */
+struct mux_state *devm_mux_state_get_optional(struct device *dev, const char *mux_name)
+{
+	return __devm_mux_state_get(dev, mux_name, true, NULL, NULL);
+}
+EXPORT_SYMBOL_GPL(devm_mux_state_get_optional);
 
-	*ptr = mstate;
-	devres_add(dev, ptr);
+/**
+ * devm_mux_state_get_selected() - Get the mux-state for a device, with
+ *				   resource management.
+ * @dev: The device that needs a mux-state.
+ * @mux_name: The name identifying the mux-state.
+ *
+ * Return: Pointer to the mux-state, or an ERR_PTR with a negative errno.
+ *
+ * The returned mux-state (if valid) is already selected.
+ *
+ * The mux-state will automatically be deselected and freed on release.
+ */
+struct mux_state *devm_mux_state_get_selected(struct device *dev, const char *mux_name)
+{
+	return __devm_mux_state_get(dev, mux_name, false, mux_state_select, mux_state_deselect);
+}
+EXPORT_SYMBOL_GPL(devm_mux_state_get_selected);
 
-	return mstate;
+/**
+ * devm_mux_state_get_optional_selected() - Get the optional mux-state for
+ *					    a device, with resource management.
+ * @dev: The device that needs a mux-state.
+ * @mux_name: The name identifying the mux-state.
+ *
+ * Return: Pointer to the mux-state on success, an ERR_PTR with a negative errno on error,
+ * or NULL if mux doesn't exist.
+ *
+ * The returned mux-state (if valid) is already selected.
+ *
+ * The mux-state will automatically be deselected and freed on release.
+ */
+struct mux_state *devm_mux_state_get_optional_selected(struct device *dev,
+						       const char *mux_name)
+{
+	return __devm_mux_state_get(dev, mux_name, true, mux_state_select, mux_state_deselect);
 }
-EXPORT_SYMBOL_GPL(devm_mux_state_get);
+EXPORT_SYMBOL_GPL(devm_mux_state_get_optional_selected);
 
 /*
  * Using subsys_initcall instead of module_init here to try to ensure - for
diff --git a/include/linux/mux/consumer.h b/include/linux/mux/consumer.h
index 2e25c838f831..3ede55b907eb 100644
--- a/include/linux/mux/consumer.h
+++ b/include/linux/mux/consumer.h
@@ -16,6 +16,8 @@ struct device;
 struct mux_control;
 struct mux_state;
 
+#ifdef CONFIG_MULTIPLEXER
+
 unsigned int mux_control_states(struct mux_control *mux);
 int __must_check mux_control_select_delay(struct mux_control *mux,
 					  unsigned int state,
@@ -54,11 +56,109 @@ int mux_control_deselect(struct mux_control *mux);
 int mux_state_deselect(struct mux_state *mstate);
 
 struct mux_control *mux_control_get(struct device *dev, const char *mux_name);
+struct mux_control *mux_control_get_optional(struct device *dev, const char *mux_name);
 void mux_control_put(struct mux_control *mux);
 
-struct mux_control *devm_mux_control_get(struct device *dev,
-					 const char *mux_name);
-struct mux_state *devm_mux_state_get(struct device *dev,
-				     const char *mux_name);
+struct mux_control *devm_mux_control_get(struct device *dev, const char *mux_name);
+struct mux_state *devm_mux_state_get(struct device *dev, const char *mux_name);
+struct mux_state *devm_mux_state_get_optional(struct device *dev, const char *mux_name);
+struct mux_state *devm_mux_state_get_selected(struct device *dev, const char *mux_name);
+struct mux_state *devm_mux_state_get_optional_selected(struct device *dev, const char *mux_name);
+
+#else
+
+static inline unsigned int mux_control_states(struct mux_control *mux)
+{
+	return 0;
+}
+static inline int __must_check mux_control_select_delay(struct mux_control *mux,
+							unsigned int state, unsigned int delay_us)
+{
+	return -EOPNOTSUPP;
+}
+static inline int __must_check mux_state_select_delay(struct mux_state *mstate,
+						      unsigned int delay_us)
+{
+	return -EOPNOTSUPP;
+}
+static inline int __must_check mux_control_try_select_delay(struct mux_control *mux,
+							    unsigned int state,
+							    unsigned int delay_us)
+{
+	return -EOPNOTSUPP;
+}
+static inline int __must_check mux_state_try_select_delay(struct mux_state *mstate,
+							  unsigned int delay_us)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int __must_check mux_control_select(struct mux_control *mux,
+						  unsigned int state)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int __must_check mux_state_select(struct mux_state *mstate)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int __must_check mux_control_try_select(struct mux_control *mux,
+						      unsigned int state)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int __must_check mux_state_try_select(struct mux_state *mstate)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int mux_control_deselect(struct mux_control *mux)
+{
+	return -EOPNOTSUPP;
+}
+static inline int mux_state_deselect(struct mux_state *mstate)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct mux_control *mux_control_get_optional(struct device *dev,
+							   const char *mux_name)
+{
+	return NULL;
+}
+static inline void mux_control_put(struct mux_control *mux) {}
+
+static inline struct mux_control *devm_mux_control_get(struct device *dev, const char *mux_name)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct mux_state *devm_mux_state_get(struct device *dev, const char *mux_name)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct mux_state *devm_mux_state_get_optional(struct device *dev,
+							    const char *mux_name)
+{
+	return NULL;
+}
+static inline struct mux_state *devm_mux_state_get_selected(struct device *dev,
+							    const char *mux_name)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+static inline struct mux_state *devm_mux_state_get_optional_selected(struct device *dev,
+								     const char *mux_name)
+{
+	return NULL;
+}
+
+#endif /* CONFIG_MULTIPLEXER */
 
 #endif /* _LINUX_MUX_CONSUMER_H */

-- 
2.43.0

[PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Josua Mayer]

Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
option thorugh the kernel configuration without explicit "select" driver
dependencies.

Select it by default when COMPILE_TEST is set for better coverage.

Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/mux/Kconfig | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
index c68132e38138..e31c46820bdf 100644
--- a/drivers/mux/Kconfig
+++ b/drivers/mux/Kconfig
@@ -4,7 +4,13 @@
 #
 
 config MULTIPLEXER
-	tristate
+	tristate "Generic Multiplexer Support" if COMPILE_TEST
+	help
+	  This framework is designed to abstract multiplexer handling for
+	  devices via various GPIO-, MMIO/Regmap or specific multiplexer
+	  controller chips.
+
+	  If unsure, say no.
 
 menu "Multiplexer drivers"
 	depends on MULTIPLEXER

-- 
2.43.0

[PATCH v8 4/7] phy: can-transceiver: drop temporary helper getting optional mux-state

[Josua Mayer]

Multiplexer subsystem has now added helpers for getting managed optional
mux-state.

Switch to the new devm_mux_state_get_optional helper.

This change is only compile-tested.

Acked-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/phy/phy-can-transceiver.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/drivers/phy/phy-can-transceiver.c b/drivers/phy/phy-can-transceiver.c
index 81591d247128..2b52e47f247a 100644
--- a/drivers/phy/phy-can-transceiver.c
+++ b/drivers/phy/phy-can-transceiver.c
@@ -126,16 +126,6 @@ static const struct of_device_id can_transceiver_phy_ids[] = {
 };
 MODULE_DEVICE_TABLE(of, can_transceiver_phy_ids);
 
-/* Temporary wrapper until the multiplexer subsystem supports optional muxes */
-static inline struct mux_state *
-temp_devm_mux_state_get_optional(struct device *dev, const char *mux_name)
-{
-	if (!of_property_present(dev->of_node, "mux-states"))
-		return NULL;
-
-	return devm_mux_state_get(dev, mux_name);
-}
-
 static struct phy *can_transceiver_phy_xlate(struct device *dev,
 					     const struct of_phandle_args *args)
 {
@@ -183,7 +173,7 @@ static int can_transceiver_phy_probe(struct platform_device *pdev)
 	priv->num_ch = num_ch;
 	platform_set_drvdata(pdev, priv);
 
-	mux_state = temp_devm_mux_state_get_optional(dev, NULL);
+	mux_state = devm_mux_state_get_optional(dev, NULL);
 	if (IS_ERR(mux_state))
 		return PTR_ERR(mux_state);
 

-- 
2.43.0

[PATCH v8 5/7] i2c: omap: switch to new generic helper for getting selected mux-state

[Josua Mayer]

Multiplexer subsystem has added generic helper functions for getting an
already selected mux-state object.

Replace existing logic in probe with the equivalent helper function.

There is a functional difference in that the mux is now automatically
deselected on release, replacing the explicit mux_state_deselect call.

This change is only compile-tested.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/i2c/busses/i2c-omap.c | 24 +++++-------------------
 1 file changed, 5 insertions(+), 19 deletions(-)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index d9f590f0c384..f02d294db42a 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -1453,27 +1453,16 @@ omap_i2c_probe(struct platform_device *pdev)
 				       (1000 * omap->speed / 8);
 	}
 
-	if (of_property_present(node, "mux-states")) {
-		struct mux_state *mux_state;
-
-		mux_state = devm_mux_state_get(&pdev->dev, NULL);
-		if (IS_ERR(mux_state)) {
-			r = PTR_ERR(mux_state);
-			dev_dbg(&pdev->dev, "failed to get I2C mux: %d\n", r);
-			goto err_put_pm;
-		}
-		omap->mux_state = mux_state;
-		r = mux_state_select(omap->mux_state);
-		if (r) {
-			dev_err(&pdev->dev, "failed to select I2C mux: %d\n", r);
-			goto err_put_pm;
-		}
+	omap->mux_state = devm_mux_state_get_optional_selected(&pdev->dev, NULL);
+	if (IS_ERR(omap->mux_state)) {
+		r = PTR_ERR(omap->mux_state);
+		goto err_put_pm;
 	}
 
 	/* reset ASAP, clearing any IRQs */
 	r = omap_i2c_init(omap);
 	if (r)
-		goto err_mux_state_deselect;
+		goto err_put_pm;
 
 	if (omap->rev < OMAP_I2C_OMAP1_REV_2)
 		r = devm_request_irq(&pdev->dev, omap->irq, omap_i2c_omap1_isr,
@@ -1515,9 +1504,6 @@ omap_i2c_probe(struct platform_device *pdev)
 
 err_unuse_clocks:
 	omap_i2c_write_reg(omap, OMAP_I2C_CON_REG, 0);
-err_mux_state_deselect:
-	if (omap->mux_state)
-		mux_state_deselect(omap->mux_state);
 err_put_pm:
 	pm_runtime_put_sync(omap->dev);
 err_disable_pm:

-- 
2.43.0

[PATCH v8 6/7] dt-bindings: mmc: renesas,sdhi: Add mux-states property

[Josua Mayer]

Add mux controller support for data or control lines that are muxed
between a host and multiple cards.

There are several devices supporting a choice of eMMC or SD on a single
board by both dip switch and gpio, e.g. Renesas RZ/G2L SMARC SoM and
SolidRun RZ/G2L SoM.

In-tree dts for the Renesas boards currently rely on preprocessor macros
and gpio hogs to describe the respective cards.

By adding mux-states property to sdhi controller description, boards can
correctly describe the mux that already exists in hardware - and drivers
can coordinate between mux selection and probing for cards.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml b/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml
index c754ea71f51f..64fac0d11329 100644
--- a/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml
+++ b/Documentation/devicetree/bindings/mmc/renesas,sdhi.yaml
@@ -106,6 +106,11 @@ properties:
   iommus:
     maxItems: 1
 
+  mux-states:
+    description:
+      mux controller node to route the SD/SDIO/eMMC signals from SoC to cards.
+    maxItems: 1
+
   power-domains:
     maxItems: 1
 
@@ -275,6 +280,7 @@ examples:
         max-frequency = <195000000>;
         power-domains = <&sysc R8A7790_PD_ALWAYS_ON>;
         resets = <&cpg 314>;
+        mux-states = <&mux 0>;
     };
 
     sdhi1: mmc@ee120000 {

-- 
2.43.0

[PATCH v8 7/7] mmc: host: renesas_sdhi_core: support selecting an optional mux

[Josua Mayer]

Some hardware designs route data or control signals through a mux to
support multiple devices on a single sdhi controller.

In particular SolidRun RZ/G2L/G2LC/V2L System on Module use a mux for
switching between soldered eMMC and an optional microSD on a carrier
board, e.g. for development or provisioning.

SD/SDIO/eMMC are not well suited for runtime switching between different
cards, however boot-time selection is possible and useful - in
particular considering dt overlays.

Add support for an optional SD/SDIO/eMMC mux defined in dt, and select
it during probe.

Similar functionality already exists in other places, e.g. i2c-omap.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Josua Mayer <josua@solid-run.com>
---
 drivers/mmc/host/renesas_sdhi_core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/mmc/host/renesas_sdhi_core.c b/drivers/mmc/host/renesas_sdhi_core.c
index 2a310a145785..f9ec78d699f4 100644
--- a/drivers/mmc/host/renesas_sdhi_core.c
+++ b/drivers/mmc/host/renesas_sdhi_core.c
@@ -26,6 +26,7 @@
 #include <linux/mmc/mmc.h>
 #include <linux/mmc/slot-gpio.h>
 #include <linux/module.h>
+#include <linux/mux/consumer.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/pinctrl/pinctrl-state.h>
 #include <linux/platform_data/tmio.h>
@@ -1062,6 +1063,7 @@ int renesas_sdhi_probe(struct platform_device *pdev,
 	struct regulator_dev *rdev;
 	struct renesas_sdhi_dma *dma_priv;
 	struct device *dev = &pdev->dev;
+	struct mux_state *mux_state;
 	struct tmio_mmc_host *host;
 	struct renesas_sdhi *priv;
 	int num_irqs, irq, ret, i;
@@ -1116,6 +1118,10 @@ int renesas_sdhi_probe(struct platform_device *pdev,
 						"state_uhs");
 	}
 
+	mux_state = devm_mux_state_get_optional_selected(&pdev->dev, NULL);
+	if (IS_ERR(mux_state))
+		return PTR_ERR(mux_state);
+
 	host = tmio_mmc_host_alloc(pdev, mmc_data);
 	if (IS_ERR(host))
 		return PTR_ERR(host);

-- 
2.43.0

Re: [PATCH v8 2/7] mux: Add helper functions for getting optional and selected mux-state

[Josua Mayer]

On 03/02/2026 15:01, Josua Mayer wrote:
> In-tree phy-can-transceiver driver has already implemented a local
> version of devm_mux_state_get_optional.
>
> The omap-i2c driver gets and selects an optional mux in its probe
> function without using any helper.
>
> Add new helper functions covering both aforementioned use-cases:
>
> - mux_control_get_optional:
>    Get a mux-control if specified in dt, return NULL otherwise.
> - devm_mux_state_get_optional:
>    Get a mux-state if specified in dt, return NULL otherwise.
> - devm_mux_state_get_selected:
>    Get and select a mux-state specified in dt, return error otherwise.
> - devm_mux_state_get_optional_selected:
>    Get and select a mux-state if specified in dt, return error or NULL.
>
> Existing mux_get helper function is changed to take an extra argument
> indicating whether the mux is optional.
> In this case no error is printed, and NULL returned in case of ENOENT.
>
> Calling code is adapted to handle NULL return case, and to pass optional
> argument as required.
>
> To support automatic deselect for _selected helper, a new structure is
> created storing an exit pointer similar to clock core which is called on
> release.
>
> To facilitate code sharing between optional/mandatory/selected helpers,
> a new internal helper function is added to handle quiet (optional) and
> verbose (mandatory) errors, as well as storing the correct callback for
> devm release: __devm_mux_state_get
>
> Due to this structure devm_mux_state_get_*_selected can no longer print
> a useful error message when select fails. Instead callers should print
> errors where needed.
>
> Commit e153fdea9db04 ("phy: can-transceiver: Re-instate "mux-states"
> property presence check") noted that "mux_get() always prints an error
> message in case of an error, including when the property is not present,
> confusing the user."
>
> The first error message covers the case that a mux name is not matched
> in dt. The second error message is based on of_parse_phandle_with_args
> return value.
>
> In optional case no error is printed and NULL is returned.
> This ensures that the new helper functions will not confuse the user
> either.
>
> With the addition of optional helper functions it became clear that
> drivers should compile and link even if CONFIG_MULTIPLEXER was not enabled.
> Add stubs for all symbols exported by mux core.
>
> Signed-off-by: Josua Mayer <josua@solid-run.com>
> ---
>   drivers/mux/core.c           | 205 ++++++++++++++++++++++++++++++++++++-------
>   include/linux/mux/consumer.h | 108 ++++++++++++++++++++++-
>   2 files changed, 278 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/mux/core.c b/drivers/mux/core.c
> index a3840fe0995f..2e8295e3aabe 100644
> --- a/drivers/mux/core.c
> +++ b/drivers/mux/core.c
> @@ -46,6 +46,16 @@ static const struct class mux_class = {
>   	.name = "mux",
>   };
>   
> +/**
> + * struct devm_mux_state_state -	Tracks managed resources for mux-state objects.
> + * @mstate:				Pointer to a mux state.
> + * @exit:				An optional callback to execute before free.
> + */
> +struct devm_mux_state_state {
> +	struct mux_state *mstate;
> +	int (*exit)(struct mux_state *mstate);
> +};
> +
>   static DEFINE_IDA(mux_ida);
>   
>   static int __init mux_init(void)
> @@ -516,17 +526,19 @@ static struct mux_chip *of_find_mux_chip_by_node(struct device_node *np)
>   	return dev ? to_mux_chip(dev) : NULL;
>   }
>   
> -/*
> +/**
>    * mux_get() - Get the mux-control for a device.
>    * @dev: The device that needs a mux-control.
>    * @mux_name: The name identifying the mux-control.
>    * @state: Pointer to where the requested state is returned, or NULL when
>    *         the required multiplexer states are handled by other means.
> + * @optional: Whether to return NULL and silence errors when mux doesn't exist.
>    *
> - * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
> + * Return: Pointer to the mux-control on success, an ERR_PTR with a negative errno on error,
> + * or NULL if optional is true and mux doesn't exist.
>    */
>   static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> -				   unsigned int *state)
> +				   unsigned int *state, bool optional)
>   {
>   	struct device_node *np = dev->of_node;
>   	struct of_phandle_args args;
> @@ -542,7 +554,9 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
>   		else
>   			index = of_property_match_string(np, "mux-control-names",
>   							 mux_name);
> -		if (index < 0) {
> +		if (index < 0 && optional) {
> +			return NULL;
> +		} else if (index < 0) {
>   			dev_err(dev, "mux controller '%s' not found\n",
>   				mux_name);
>   			return ERR_PTR(index);
> @@ -558,8 +572,12 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
>   						 "mux-controls", "#mux-control-cells",
>   						 index, &args);
>   	if (ret) {
> +		if (optional && ret == -ENOENT)
> +			return NULL;
> +
>   		dev_err(dev, "%pOF: failed to get mux-%s %s(%i)\n",
> -			np, state ? "state" : "control", mux_name ?: "", index);
> +			np, state ? "state" : "control",
> +			mux_name ?: "", index);
>   		return ERR_PTR(ret);
>   	}
>   
> @@ -617,10 +635,28 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
>    */
>   struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
>   {
> -	return mux_get(dev, mux_name, NULL);
> +	struct mux_control *mux = mux_get(dev, mux_name, NULL, false);
> +
> +	if (!mux)
> +		return ERR_PTR(-ENOENT);
> +
> +	return mux;
>   }
>   EXPORT_SYMBOL_GPL(mux_control_get);
>   
> +/**
> + * mux_control_get_optional() - Get the optional mux-control for a device.
> + * @dev: The device that needs a mux-control.
> + * @mux_name: The name identifying the mux-control.
> + *
> + * Return: A pointer to the mux-control, an ERR_PTR with a negative errno.
  * Return: Pointer to the mux-state on success, an ERR_PTR with a 
negative errno on error,
  * or NULL if mux doesn't exist.

If there will be v9, I shall change this to be more precise similar to 
other functions.
> + */
> +struct mux_control *mux_control_get_optional(struct device *dev, const char *mux_name)
> +{
> +	return mux_get(dev, mux_name, NULL, true);
> +}
> +EXPORT_SYMBOL_GPL(mux_control_get_optional);
> +
>   /**
>    * mux_control_put() - Put away the mux-control for good.
>    * @mux: The mux-control to put away.
> @@ -657,10 +693,13 @@ struct mux_control *devm_mux_control_get(struct device *dev,
>   	if (!ptr)
>   		return ERR_PTR(-ENOMEM);
>   
> -	mux = mux_control_get(dev, mux_name);
> +	mux = mux_get(dev, mux_name, NULL, false);
>   	if (IS_ERR(mux)) {
>   		devres_free(ptr);
>   		return mux;
> +	} else if (!mux) {
> +		devres_free(ptr);
> +		return ERR_PTR(-ENOENT);
>   	}
>   
>   	*ptr = mux;
> @@ -670,14 +709,16 @@ struct mux_control *devm_mux_control_get(struct device *dev,
>   }
>   EXPORT_SYMBOL_GPL(devm_mux_control_get);
>   
> -/*
> +/**
>    * mux_state_get() - Get the mux-state for a device.
>    * @dev: The device that needs a mux-state.
>    * @mux_name: The name identifying the mux-state.
> + * @optional: Whether to return NULL and silence errors when mux doesn't exist.
>    *
> - * Return: A pointer to the mux-state, or an ERR_PTR with a negative errno.
> + * Return: Pointer to the mux-state on success, an ERR_PTR with a negative errno on error,
> + * or NULL if optional is true and mux doesn't exist.
>    */
> -static struct mux_state *mux_state_get(struct device *dev, const char *mux_name)
> +static struct mux_state *mux_state_get(struct device *dev, const char *mux_name, bool optional)
>   {
>   	struct mux_state *mstate;
>   
...

Re: [PATCH v8 2/7] mux: Add helper functions for getting optional and selected mux-state

[Ulf Hansson]

On Tue, 3 Feb 2026 at 16:35, Josua Mayer <josua@solid-run.com> wrote:
>
> On 03/02/2026 15:01, Josua Mayer wrote:
> > In-tree phy-can-transceiver driver has already implemented a local
> > version of devm_mux_state_get_optional.
> >
> > The omap-i2c driver gets and selects an optional mux in its probe
> > function without using any helper.
> >
> > Add new helper functions covering both aforementioned use-cases:
> >
> > - mux_control_get_optional:
> >    Get a mux-control if specified in dt, return NULL otherwise.
> > - devm_mux_state_get_optional:
> >    Get a mux-state if specified in dt, return NULL otherwise.
> > - devm_mux_state_get_selected:
> >    Get and select a mux-state specified in dt, return error otherwise.
> > - devm_mux_state_get_optional_selected:
> >    Get and select a mux-state if specified in dt, return error or NULL.
> >
> > Existing mux_get helper function is changed to take an extra argument
> > indicating whether the mux is optional.
> > In this case no error is printed, and NULL returned in case of ENOENT.
> >
> > Calling code is adapted to handle NULL return case, and to pass optional
> > argument as required.
> >
> > To support automatic deselect for _selected helper, a new structure is
> > created storing an exit pointer similar to clock core which is called on
> > release.
> >
> > To facilitate code sharing between optional/mandatory/selected helpers,
> > a new internal helper function is added to handle quiet (optional) and
> > verbose (mandatory) errors, as well as storing the correct callback for
> > devm release: __devm_mux_state_get
> >
> > Due to this structure devm_mux_state_get_*_selected can no longer print
> > a useful error message when select fails. Instead callers should print
> > errors where needed.
> >
> > Commit e153fdea9db04 ("phy: can-transceiver: Re-instate "mux-states"
> > property presence check") noted that "mux_get() always prints an error
> > message in case of an error, including when the property is not present,
> > confusing the user."
> >
> > The first error message covers the case that a mux name is not matched
> > in dt. The second error message is based on of_parse_phandle_with_args
> > return value.
> >
> > In optional case no error is printed and NULL is returned.
> > This ensures that the new helper functions will not confuse the user
> > either.
> >
> > With the addition of optional helper functions it became clear that
> > drivers should compile and link even if CONFIG_MULTIPLEXER was not enabled.
> > Add stubs for all symbols exported by mux core.
> >
> > Signed-off-by: Josua Mayer <josua@solid-run.com>
> > ---
> >   drivers/mux/core.c           | 205 ++++++++++++++++++++++++++++++++++++-------
> >   include/linux/mux/consumer.h | 108 ++++++++++++++++++++++-
> >   2 files changed, 278 insertions(+), 35 deletions(-)
> >
> > diff --git a/drivers/mux/core.c b/drivers/mux/core.c
> > index a3840fe0995f..2e8295e3aabe 100644
> > --- a/drivers/mux/core.c
> > +++ b/drivers/mux/core.c
> > @@ -46,6 +46,16 @@ static const struct class mux_class = {
> >       .name = "mux",
> >   };
> >
> > +/**
> > + * struct devm_mux_state_state -     Tracks managed resources for mux-state objects.
> > + * @mstate:                          Pointer to a mux state.
> > + * @exit:                            An optional callback to execute before free.
> > + */
> > +struct devm_mux_state_state {
> > +     struct mux_state *mstate;
> > +     int (*exit)(struct mux_state *mstate);
> > +};
> > +
> >   static DEFINE_IDA(mux_ida);
> >
> >   static int __init mux_init(void)
> > @@ -516,17 +526,19 @@ static struct mux_chip *of_find_mux_chip_by_node(struct device_node *np)
> >       return dev ? to_mux_chip(dev) : NULL;
> >   }
> >
> > -/*
> > +/**
> >    * mux_get() - Get the mux-control for a device.
> >    * @dev: The device that needs a mux-control.
> >    * @mux_name: The name identifying the mux-control.
> >    * @state: Pointer to where the requested state is returned, or NULL when
> >    *         the required multiplexer states are handled by other means.
> > + * @optional: Whether to return NULL and silence errors when mux doesn't exist.
> >    *
> > - * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
> > + * Return: Pointer to the mux-control on success, an ERR_PTR with a negative errno on error,
> > + * or NULL if optional is true and mux doesn't exist.
> >    */
> >   static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> > -                                unsigned int *state)
> > +                                unsigned int *state, bool optional)
> >   {
> >       struct device_node *np = dev->of_node;
> >       struct of_phandle_args args;
> > @@ -542,7 +554,9 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> >               else
> >                       index = of_property_match_string(np, "mux-control-names",
> >                                                        mux_name);
> > -             if (index < 0) {
> > +             if (index < 0 && optional) {
> > +                     return NULL;
> > +             } else if (index < 0) {
> >                       dev_err(dev, "mux controller '%s' not found\n",
> >                               mux_name);
> >                       return ERR_PTR(index);
> > @@ -558,8 +572,12 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> >                                                "mux-controls", "#mux-control-cells",
> >                                                index, &args);
> >       if (ret) {
> > +             if (optional && ret == -ENOENT)
> > +                     return NULL;
> > +
> >               dev_err(dev, "%pOF: failed to get mux-%s %s(%i)\n",
> > -                     np, state ? "state" : "control", mux_name ?: "", index);
> > +                     np, state ? "state" : "control",
> > +                     mux_name ?: "", index);
> >               return ERR_PTR(ret);
> >       }
> >
> > @@ -617,10 +635,28 @@ static struct mux_control *mux_get(struct device *dev, const char *mux_name,
> >    */
> >   struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
> >   {
> > -     return mux_get(dev, mux_name, NULL);
> > +     struct mux_control *mux = mux_get(dev, mux_name, NULL, false);
> > +
> > +     if (!mux)
> > +             return ERR_PTR(-ENOENT);
> > +
> > +     return mux;
> >   }
> >   EXPORT_SYMBOL_GPL(mux_control_get);
> >
> > +/**
> > + * mux_control_get_optional() - Get the optional mux-control for a device.
> > + * @dev: The device that needs a mux-control.
> > + * @mux_name: The name identifying the mux-control.
> > + *
> > + * Return: A pointer to the mux-control, an ERR_PTR with a negative errno.
>   * Return: Pointer to the mux-state on success, an ERR_PTR with a
> negative errno on error,
>   * or NULL if mux doesn't exist.
>
> If there will be v9, I shall change this to be more precise similar to
> other functions.

The series looks good to me!

I can queue the series for v7.0 via my mmc tree and amend the change
according to above when applying, but I need the ack from Wolfram on
the i2c patch (patch5) first.

If this doesn't make it for v7.0, I suggest you re-spin a v9 after the
merge window.

Kind regards
Uffe



> > + */
> > +struct mux_control *mux_control_get_optional(struct device *dev, const char *mux_name)
> > +{
> > +     return mux_get(dev, mux_name, NULL, true);
> > +}
> > +EXPORT_SYMBOL_GPL(mux_control_get_optional);
> > +
> >   /**
> >    * mux_control_put() - Put away the mux-control for good.
> >    * @mux: The mux-control to put away.
> > @@ -657,10 +693,13 @@ struct mux_control *devm_mux_control_get(struct device *dev,
> >       if (!ptr)
> >               return ERR_PTR(-ENOMEM);
> >
> > -     mux = mux_control_get(dev, mux_name);
> > +     mux = mux_get(dev, mux_name, NULL, false);
> >       if (IS_ERR(mux)) {
> >               devres_free(ptr);
> >               return mux;
> > +     } else if (!mux) {
> > +             devres_free(ptr);
> > +             return ERR_PTR(-ENOENT);
> >       }
> >
> >       *ptr = mux;
> > @@ -670,14 +709,16 @@ struct mux_control *devm_mux_control_get(struct device *dev,
> >   }
> >   EXPORT_SYMBOL_GPL(devm_mux_control_get);
> >
> > -/*
> > +/**
> >    * mux_state_get() - Get the mux-state for a device.
> >    * @dev: The device that needs a mux-state.
> >    * @mux_name: The name identifying the mux-state.
> > + * @optional: Whether to return NULL and silence errors when mux doesn't exist.
> >    *
> > - * Return: A pointer to the mux-state, or an ERR_PTR with a negative errno.
> > + * Return: Pointer to the mux-state on success, an ERR_PTR with a negative errno on error,
> > + * or NULL if optional is true and mux doesn't exist.
> >    */
> > -static struct mux_state *mux_state_get(struct device *dev, const char *mux_name)
> > +static struct mux_state *mux_state_get(struct device *dev, const char *mux_name, bool optional)
> >   {
> >       struct mux_state *mstate;
> >
> ...

Re: [PATCH v8 1/7] phy: can-transceiver: rename temporary helper function to avoid conflict

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:34PM +0200, Josua Mayer wrote:
> Rename the temporary devm_mux_state_get_optional function to avoid
> conflict with upcoming implementation in multiplexer subsystem.
> 
> Acked-by: Vinod Koul <vkoul@kernel.org>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Josua Mayer <josua@solid-run.com>

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 2/7] mux: Add helper functions for getting optional and selected mux-state

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:35PM +0200, Josua Mayer wrote:
> In-tree phy-can-transceiver driver has already implemented a local
> version of devm_mux_state_get_optional.
> 
> The omap-i2c driver gets and selects an optional mux in its probe
> function without using any helper.
> 
> Add new helper functions covering both aforementioned use-cases:
> 
> - mux_control_get_optional:
>   Get a mux-control if specified in dt, return NULL otherwise.
> - devm_mux_state_get_optional:
>   Get a mux-state if specified in dt, return NULL otherwise.
> - devm_mux_state_get_selected:
>   Get and select a mux-state specified in dt, return error otherwise.
> - devm_mux_state_get_optional_selected:
>   Get and select a mux-state if specified in dt, return error or NULL.
> 
> Existing mux_get helper function is changed to take an extra argument
> indicating whether the mux is optional.
> In this case no error is printed, and NULL returned in case of ENOENT.
> 
> Calling code is adapted to handle NULL return case, and to pass optional
> argument as required.
> 
> To support automatic deselect for _selected helper, a new structure is
> created storing an exit pointer similar to clock core which is called on
> release.
> 
> To facilitate code sharing between optional/mandatory/selected helpers,
> a new internal helper function is added to handle quiet (optional) and
> verbose (mandatory) errors, as well as storing the correct callback for
> devm release: __devm_mux_state_get
> 
> Due to this structure devm_mux_state_get_*_selected can no longer print
> a useful error message when select fails. Instead callers should print
> errors where needed.
> 
> Commit e153fdea9db04 ("phy: can-transceiver: Re-instate "mux-states"
> property presence check") noted that "mux_get() always prints an error
> message in case of an error, including when the property is not present,
> confusing the user."
> 
> The first error message covers the case that a mux name is not matched
> in dt. The second error message is based on of_parse_phandle_with_args
> return value.
> 
> In optional case no error is printed and NULL is returned.
> This ensures that the new helper functions will not confuse the user
> either.
> 
> With the addition of optional helper functions it became clear that
> drivers should compile and link even if CONFIG_MULTIPLEXER was not enabled.
> Add stubs for all symbols exported by mux core.
> 
> Signed-off-by: Josua Mayer <josua@solid-run.com>

I trust you guys with this one. I think the interfaces are useful,
though, so maybe like this?

Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:36PM +0200, Josua Mayer wrote:
> Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
> option thorugh the kernel configuration without explicit "select" driver
> dependencies.
> 
> Select it by default when COMPILE_TEST is set for better coverage.
> 
> Signed-off-by: Josua Mayer <josua@solid-run.com>

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 4/7] phy: can-transceiver: drop temporary helper getting optional mux-state

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:37PM +0200, Josua Mayer wrote:
> Multiplexer subsystem has now added helpers for getting managed optional
> mux-state.
> 
> Switch to the new devm_mux_state_get_optional helper.
> 
> This change is only compile-tested.
> 
> Acked-by: Vinod Koul <vkoul@kernel.org>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Josua Mayer <josua@solid-run.com>

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 5/7] i2c: omap: switch to new generic helper for getting selected mux-state

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:38PM +0200, Josua Mayer wrote:
> Multiplexer subsystem has added generic helper functions for getting an
> already selected mux-state object.
> 
> Replace existing logic in probe with the equivalent helper function.
> 
> There is a functional difference in that the mux is now automatically
> deselected on release, replacing the explicit mux_state_deselect call.
> 
> This change is only compile-tested.
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Reviewed-by: Andreas Kemnade <andreas@kemnade.info>
> Signed-off-by: Josua Mayer <josua@solid-run.com>

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 6/7] dt-bindings: mmc: renesas,sdhi: Add mux-states property

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:39PM +0200, Josua Mayer wrote:
> Add mux controller support for data or control lines that are muxed
> between a host and multiple cards.
> 
> There are several devices supporting a choice of eMMC or SD on a single
> board by both dip switch and gpio, e.g. Renesas RZ/G2L SMARC SoM and
> SolidRun RZ/G2L SoM.
> 
> In-tree dts for the Renesas boards currently rely on preprocessor macros
> and gpio hogs to describe the respective cards.
> 
> By adding mux-states property to sdhi controller description, boards can
> correctly describe the mux that already exists in hardware - and drivers
> can coordinate between mux selection and probing for cards.
> 
> Acked-by: Rob Herring (Arm) <robh@kernel.org>
> Signed-off-by: Josua Mayer <josua@solid-run.com>

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 7/7] mmc: host: renesas_sdhi_core: support selecting an optional mux

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:40PM +0200, Josua Mayer wrote:
> Some hardware designs route data or control signals through a mux to
> support multiple devices on a single sdhi controller.
> 
> In particular SolidRun RZ/G2L/G2LC/V2L System on Module use a mux for
> switching between soldered eMMC and an optional microSD on a carrier
> board, e.g. for development or provisioning.
> 
> SD/SDIO/eMMC are not well suited for runtime switching between different
> cards, however boot-time selection is possible and useful - in
> particular considering dt overlays.
> 
> Add support for an optional SD/SDIO/eMMC mux defined in dt, and select
> it during probe.
> 
> Similar functionality already exists in other places, e.g. i2c-omap.
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Josua Mayer <josua@solid-run.com>

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 0/7] mmc: host: renesas_sdhi_core: support configuring an optional sdio mux

[Ulf Hansson]

On Tue, 3 Feb 2026 at 14:01, Josua Mayer <josua@solid-run.com> wrote:
>
> Some Renesas SoC based boards mux SD and eMMC on a single sdio
> controller, exposing user control by dip switch and software control by
> gpio.
>
> Purpose is to simplify development and provisioning by selecting boot
> media at power-on, and again before starting linux.
>
> Add binding and driver support for linking a (gpio) mux to renesas sdio
> controller.
>
> Introduce generic helper functions for getting managed and selected
> mux-state objects, and switch i2c-omap and phy-can-transceiver drivers.
>
> Signed-off-by: Josua Mayer <josua@solid-run.com>
> ---
> Changes in v8:
> - Add defensive null checks for all non-optional calls to internal
>   mux_get function.
> - Document NULL return value on applicable functions.
> - Avoid IS_ERR_OR_NULL and ERR_PTR(0) to disarm smatch errors.
> - Link to v7: https://lore.kernel.org/r/20260128-rz-sdio-mux-v7-0-92ebb6da0df8@solid-run.com
>
> Changes in v7:
> - picked up reviewed-tags
> - fix Kconfig change to add the missing prompt for CONFIG_MULTIPLEXER,
>   and enable it by default when COMPILE_TEST is set.
>   (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
> - fix another kernel build robot warning: undocumented C struct member
> - Link to v6: https://lore.kernel.org/r/20260121-rz-sdio-mux-v6-0-38aa39527928@solid-run.com
>
> Changes in v6:
> - replaced /* with /** for devm_mux_state_state function description.
> - collected review tags.
> - fixed checkpatch warnings (space-before-tab, void-return).
>   (Reported-by: Geert Uytterhoeven)
> - fixed use-after-free in mux core mux_get function.
>   (Reported-by: Geert Uytterhoeven)
> - fix mux helper error path uninitialised return code variable.
>   (Reported-by: kernel test robot <lkp@intel.com>)
> - Link to v5: https://lore.kernel.org/r/20260118-rz-sdio-mux-v5-0-3c37e8872683@solid-run.com
>
> Changes in v5:
> - implemented automatic mux deselect for devm_*_selected.
>   (Reported-by: Wolfram Sang <wsa+renesas@sang-engineering.com>)
> - because of semantic changes I dropped reviewed and acks from omap-i2c
>   patch (Andreas Kemnade / Wolfram Sang).
> - fix invalid return value in void function for mux helper stubs
>   (Reported-by: kernel test robot <lkp@intel.com>)
> - Link to v4: https://lore.kernel.org/r/20251229-rz-sdio-mux-v4-0-a023e55758fe@solid-run.com
>
> Changes in v4:
> - added MULTIPLEXER Kconfig help text.
> - removed "select MULTIPLEXER" from renesas sdhi Kconfig, as it is
>   not required for all devices using this driver.
> - added stubs for all symbols exported by mux core.
>   (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
> - refactored mux core logic to silence ENOENT errors only on optional
>   code paths, keeping error printing unchanged otherwise.
>   (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
> - picked up various reviewed- and acked-by tags
> - Link to v3: https://lore.kernel.org/r/20251210-rz-sdio-mux-v3-0-ca628db56d60@solid-run.com
>
> Changes in v3:
> - updated omap-i2c and phy-can-transceiver to use new helpers.
> - created generic helper functions for getting managed optional mux-state.
>   (Reported-by: Rob Herring <robh@kernel.org>)
> - picked up binding ack by Rob Herring.
> - replaced use of "SDIO" with "SD/SDIO/eMMC" in binding document and
>   commit descriptions.
>   (Reported-by: Ulf Hansson <ulf.hansson@linaro.org>)
> - Link to v2: https://lore.kernel.org/r/20251201-rz-sdio-mux-v2-0-bcb581b88dd7@solid-run.com
>
> Changes in v2:
> - dropped mux-controller node from dt binding example
>   (Reported-by: Conor Dooley <conor@kernel.org>
>    Reported-by: Krzysztof Kozlowski <krzk@kernel.org>)
> - Link to v1: https://lore.kernel.org/r/20251128-rz-sdio-mux-v1-0-1ede318d160f@solid-run.com
>
> ---
> Josua Mayer (7):
>       phy: can-transceiver: rename temporary helper function to avoid conflict
>       mux: Add helper functions for getting optional and selected mux-state
>       mux: add help text for MULTIPLEXER config option
>       phy: can-transceiver: drop temporary helper getting optional mux-state
>       i2c: omap: switch to new generic helper for getting selected mux-state
>       dt-bindings: mmc: renesas,sdhi: Add mux-states property
>       mmc: host: renesas_sdhi_core: support selecting an optional mux
>
>  .../devicetree/bindings/mmc/renesas,sdhi.yaml      |   6 +
>  drivers/i2c/busses/i2c-omap.c                      |  24 +--
>  drivers/mmc/host/renesas_sdhi_core.c               |   6 +
>  drivers/mux/Kconfig                                |   8 +-
>  drivers/mux/core.c                                 | 205 +++++++++++++++++----
>  drivers/phy/phy-can-transceiver.c                  |  10 -
>  include/linux/mux/consumer.h                       | 108 ++++++++++-
>  7 files changed, 302 insertions(+), 65 deletions(-)
> ---
> base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> change-id: 20251128-rz-sdio-mux-acc5137f1618
>
> Best regards,
> --
> Josua Mayer <josua@solid-run.com>
>
>

The series applied for next, thanks!

Kind regards
Uffe

Re: [PATCH v8 7/7] mmc: host: renesas_sdhi_core: support selecting an optional mux

[Wolfram Sang]

On Tue, Feb 03, 2026 at 03:01:40PM +0200, Josua Mayer wrote:
> Some hardware designs route data or control signals through a mux to
> support multiple devices on a single sdhi controller.
> 
> In particular SolidRun RZ/G2L/G2LC/V2L System on Module use a mux for
> switching between soldered eMMC and an optional microSD on a carrier
> board, e.g. for development or provisioning.
> 
> SD/SDIO/eMMC are not well suited for runtime switching between different
> cards, however boot-time selection is possible and useful - in
> particular considering dt overlays.
> 
> Add support for an optional SD/SDIO/eMMC mux defined in dt, and select
> it during probe.
> 
> Similar functionality already exists in other places, e.g. i2c-omap.
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Josua Mayer <josua@solid-run.com>

And to confirm the obvious, no regression found on a Renesas SparrowHawk
(R-Car V4H) not using muxes:

Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Josua Mayer]

On 03/02/2026 15:01, Josua Mayer wrote:
> Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
> option thorugh the kernel configuration without explicit "select" driver
> dependencies.
>
> Select it by default when COMPILE_TEST is set for better coverage.
>
> Signed-off-by: Josua Mayer <josua@solid-run.com>
> ---
>   drivers/mux/Kconfig | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
> index c68132e38138..e31c46820bdf 100644
> --- a/drivers/mux/Kconfig
> +++ b/drivers/mux/Kconfig
> @@ -4,7 +4,13 @@
>   #
>   
>   config MULTIPLEXER
> -	tristate
> +	tristate "Generic Multiplexer Support" if COMPILE_TEST

This didn't do what I thought it would.
It was my intention to allow enabling this through menuconfig / .config.

With the syntax above menuconfig shows:

│ Symbol: MULTIPLEXER [=n]
│ Type  : tristate
│ Defined at drivers/mux/Kconfig:6
│   Prompt: Generic Multiplexer Support
│   Visible if: COMPILE_TEST [=n]

This means it cannot be selected.

Instead I (think I) should use
default m if COMPILE_TEST

Since my patch-set broke x86_64 allmodconfig and failed merge into 
linux-next,
this presents an opportunity to change the above as well with v9.

> +	help
> +	  This framework is designed to abstract multiplexer handling for
> +	  devices via various GPIO-, MMIO/Regmap or specific multiplexer
> +	  controller chips.
> +
> +	  If unsure, say no.
>   
>   menu "Multiplexer drivers"
>   	depends on MULTIPLEXER
>

Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Geert Uytterhoeven]

Hi Josua,

On Sun, 8 Feb 2026 at 16:16, Josua Mayer <josua@solid-run.com> wrote:
> On 03/02/2026 15:01, Josua Mayer wrote:
> > Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
> > option thorugh the kernel configuration without explicit "select" driver
> > dependencies.
> >
> > Select it by default when COMPILE_TEST is set for better coverage.
> >
> > Signed-off-by: Josua Mayer <josua@solid-run.com>
> > ---
> >   drivers/mux/Kconfig | 8 +++++++-
> >   1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
> > index c68132e38138..e31c46820bdf 100644
> > --- a/drivers/mux/Kconfig
> > +++ b/drivers/mux/Kconfig
> > @@ -4,7 +4,13 @@
> >   #
> >
> >   config MULTIPLEXER
> > -     tristate
> > +     tristate "Generic Multiplexer Support" if COMPILE_TEST
>
> This didn't do what I thought it would.
> It was my intention to allow enabling this through menuconfig / .config.
>
> With the syntax above menuconfig shows:
>
> │ Symbol: MULTIPLEXER [=n]
> │ Type  : tristate
> │ Defined at drivers/mux/Kconfig:6
> │   Prompt: Generic Multiplexer Support
> │   Visible if: COMPILE_TEST [=n]
>
> This means it cannot be selected.

Looks like you haven't enabled COMPILE_TEST first?

> Instead I (think I) should use
> default m if COMPILE_TEST

No, merely enabling COMPILE_TEST must not enable additional
functionality.

> Since my patch-set broke x86_64 allmodconfig and failed merge into
> linux-next,
> this presents an opportunity to change the above as well with v9.

Ulf has already applied this series to mmc/next.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Josua Mayer]

On 09/02/2026 10:06, Geert Uytterhoeven wrote:
> Hi Josua,
>
> On Sun, 8 Feb 2026 at 16:16, Josua Mayer <josua@solid-run.com> wrote:
>> On 03/02/2026 15:01, Josua Mayer wrote:
>>> Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
>>> option thorugh the kernel configuration without explicit "select" driver
>>> dependencies.
>>>
>>> Select it by default when COMPILE_TEST is set for better coverage.
>>>
>>> Signed-off-by: Josua Mayer <josua@solid-run.com>
>>> ---
>>>    drivers/mux/Kconfig | 8 +++++++-
>>>    1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
>>> index c68132e38138..e31c46820bdf 100644
>>> --- a/drivers/mux/Kconfig
>>> +++ b/drivers/mux/Kconfig
>>> @@ -4,7 +4,13 @@
>>>    #
>>>
>>>    config MULTIPLEXER
>>> -     tristate
>>> +     tristate "Generic Multiplexer Support" if COMPILE_TEST
>> This didn't do what I thought it would.
>> It was my intention to allow enabling this through menuconfig / .config.
>>
>> With the syntax above menuconfig shows:
>>
>> │ Symbol: MULTIPLEXER [=n]
>> │ Type  : tristate
>> │ Defined at drivers/mux/Kconfig:6
>> │   Prompt: Generic Multiplexer Support
>> │   Visible if: COMPILE_TEST [=n]
>>
>> This means it cannot be selected.
> Looks like you haven't enabled COMPILE_TEST first?
Correct.
But CONFIG_MULTIPLEXER should be visible always,
not just when COMPILE_TEST is set.
>
>> Instead I (think I) should use
>> default m if COMPILE_TEST
> No, merely enabling COMPILE_TEST must not enable additional
> functionality.
>
>> Since my patch-set broke x86_64 allmodconfig and failed merge into
>> linux-next,
>> this presents an opportunity to change the above as well with v9.
> Ulf has already applied this series to mmc/next.
What would be the process to fix the build error for x86_64 allmodconfig 
now?
>
> Gr{oetje,eeting}s,
>
>                          Geert
>

Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Geert Uytterhoeven]

Hi Josua,

On Mon, 9 Feb 2026 at 11:12, Josua Mayer <josua@solid-run.com> wrote:
> On 09/02/2026 10:06, Geert Uytterhoeven wrote:
> > On Sun, 8 Feb 2026 at 16:16, Josua Mayer <josua@solid-run.com> wrote:
> >> On 03/02/2026 15:01, Josua Mayer wrote:
> >>> Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
> >>> option thorugh the kernel configuration without explicit "select" driver
> >>> dependencies.
> >>>
> >>> Select it by default when COMPILE_TEST is set for better coverage.
> >>>
> >>> Signed-off-by: Josua Mayer <josua@solid-run.com>
> >>> ---
> >>>    drivers/mux/Kconfig | 8 +++++++-
> >>>    1 file changed, 7 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
> >>> index c68132e38138..e31c46820bdf 100644
> >>> --- a/drivers/mux/Kconfig
> >>> +++ b/drivers/mux/Kconfig
> >>> @@ -4,7 +4,13 @@
> >>>    #
> >>>
> >>>    config MULTIPLEXER
> >>> -     tristate
> >>> +     tristate "Generic Multiplexer Support" if COMPILE_TEST
> >> This didn't do what I thought it would.
> >> It was my intention to allow enabling this through menuconfig / .config.
> >>
> >> With the syntax above menuconfig shows:
> >>
> >> │ Symbol: MULTIPLEXER [=n]
> >> │ Type  : tristate
> >> │ Defined at drivers/mux/Kconfig:6
> >> │   Prompt: Generic Multiplexer Support
> >> │   Visible if: COMPILE_TEST [=n]
> >>
> >> This means it cannot be selected.
> > Looks like you haven't enabled COMPILE_TEST first?
> Correct.
> But CONFIG_MULTIPLEXER should be visible always,
> not just when COMPILE_TEST is set.

Why should it always be visible? All users select it?

> >> Instead I (think I) should use
> >> default m if COMPILE_TEST
> > No, merely enabling COMPILE_TEST must not enable additional
> > functionality.
> >
> >> Since my patch-set broke x86_64 allmodconfig and failed merge into
> >> linux-next,
> >> this presents an opportunity to change the above as well with v9.
> > Ulf has already applied this series to mmc/next.
> What would be the process to fix the build error for x86_64 allmodconfig
> now?

Incremental patches, cfr. Ulf's response to [PATCH v9 0/7].

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Josua Mayer]

On 09/02/2026 12:17, Geert Uytterhoeven wrote:
> Hi Josua,
>
> On Mon, 9 Feb 2026 at 11:12, Josua Mayer <josua@solid-run.com> wrote:
>> On 09/02/2026 10:06, Geert Uytterhoeven wrote:
>>> On Sun, 8 Feb 2026 at 16:16, Josua Mayer <josua@solid-run.com> wrote:
>>>> On 03/02/2026 15:01, Josua Mayer wrote:
>>>>> Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
>>>>> option thorugh the kernel configuration without explicit "select" driver
>>>>> dependencies.
>>>>>
>>>>> Select it by default when COMPILE_TEST is set for better coverage.
>>>>>
>>>>> Signed-off-by: Josua Mayer <josua@solid-run.com>
>>>>> ---
>>>>>     drivers/mux/Kconfig | 8 +++++++-
>>>>>     1 file changed, 7 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
>>>>> index c68132e38138..e31c46820bdf 100644
>>>>> --- a/drivers/mux/Kconfig
>>>>> +++ b/drivers/mux/Kconfig
>>>>> @@ -4,7 +4,13 @@
>>>>>     #
>>>>>
>>>>>     config MULTIPLEXER
>>>>> -     tristate
>>>>> +     tristate "Generic Multiplexer Support" if COMPILE_TEST
>>>> This didn't do what I thought it would.
>>>> It was my intention to allow enabling this through menuconfig / .config.
>>>>
>>>> With the syntax above menuconfig shows:
>>>>
>>>> │ Symbol: MULTIPLEXER [=n]
>>>> │ Type  : tristate
>>>> │ Defined at drivers/mux/Kconfig:6
>>>> │   Prompt: Generic Multiplexer Support
>>>> │   Visible if: COMPILE_TEST [=n]
>>>>
>>>> This means it cannot be selected.
>>> Looks like you haven't enabled COMPILE_TEST first?
>> Correct.
>> But CONFIG_MULTIPLEXER should be visible always,
>> not just when COMPILE_TEST is set.
> Why should it always be visible? All users select it?

This is not relevant for v7 now and can be handled later.

It was discussed previously that drivers supporting optional muxes
do not need to "select" MULTIPLEXER through Kconfig,
E.g. the renesas sdhi driver.

However other drivers are already selecting it even though the mux
is optional, see e.g. phy-can-transceiver.

In order to support muxes in renesas sdhi driver e.g., users must choose to
enable both the renesas driver, and multiplexer subsystem via the 
configuration.

The mux core standalone also supports a limited use-case without other 
driver
interactions, setting idle-state e.g.:

mux-controller {
     compatible = "gpio-mux";
     #mux-control-cells = <0>;
     mux-gpios = <&tca6416_u20 0 GPIO_ACTIVE_HIGH>;
     idle-state = <0>;
};

So it can be generally useful for a user to enable CONFIG_MULTIPLEXER.

>
>>>> Instead I (think I) should use
>>>> default m if COMPILE_TEST
>>> No, merely enabling COMPILE_TEST must not enable additional
>>> functionality.
>>>
>>>> Since my patch-set broke x86_64 allmodconfig and failed merge into
>>>> linux-next,
>>>> this presents an opportunity to change the above as well with v9.
>>> Ulf has already applied this series to mmc/next.
>> What would be the process to fix the build error for x86_64 allmodconfig
>> now?
> Incremental patches, cfr. Ulf's response to [PATCH v9 0/7].
>
> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds

Re: [PATCH v8 3/7] mux: add help text for MULTIPLEXER config option

[Geert Uytterhoeven]

Hi Josua,

On Mon, 9 Feb 2026 at 11:47, Josua Mayer <josua@solid-run.com> wrote:
> On 09/02/2026 12:17, Geert Uytterhoeven wrote:
> > On Mon, 9 Feb 2026 at 11:12, Josua Mayer <josua@solid-run.com> wrote:
> >> On 09/02/2026 10:06, Geert Uytterhoeven wrote:
> >>> On Sun, 8 Feb 2026 at 16:16, Josua Mayer <josua@solid-run.com> wrote:
> >>>> On 03/02/2026 15:01, Josua Mayer wrote:
> >>>>> Add prompt and help text for CONFIG_MULTIPLEXER to allow enabling this
> >>>>> option thorugh the kernel configuration without explicit "select" driver
> >>>>> dependencies.
> >>>>>
> >>>>> Select it by default when COMPILE_TEST is set for better coverage.
> >>>>>
> >>>>> Signed-off-by: Josua Mayer <josua@solid-run.com>
> >>>>> ---
> >>>>>     drivers/mux/Kconfig | 8 +++++++-
> >>>>>     1 file changed, 7 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/mux/Kconfig b/drivers/mux/Kconfig
> >>>>> index c68132e38138..e31c46820bdf 100644
> >>>>> --- a/drivers/mux/Kconfig
> >>>>> +++ b/drivers/mux/Kconfig
> >>>>> @@ -4,7 +4,13 @@
> >>>>>     #
> >>>>>
> >>>>>     config MULTIPLEXER
> >>>>> -     tristate
> >>>>> +     tristate "Generic Multiplexer Support" if COMPILE_TEST
> >>>> This didn't do what I thought it would.
> >>>> It was my intention to allow enabling this through menuconfig / .config.
> >>>>
> >>>> With the syntax above menuconfig shows:
> >>>>
> >>>> │ Symbol: MULTIPLEXER [=n]
> >>>> │ Type  : tristate
> >>>> │ Defined at drivers/mux/Kconfig:6
> >>>> │   Prompt: Generic Multiplexer Support
> >>>> │   Visible if: COMPILE_TEST [=n]
> >>>>
> >>>> This means it cannot be selected.
> >>> Looks like you haven't enabled COMPILE_TEST first?
> >> Correct.
> >> But CONFIG_MULTIPLEXER should be visible always,
> >> not just when COMPILE_TEST is set.
> > Why should it always be visible? All users select it?
>
> This is not relevant for v7 now and can be handled later.
>
> It was discussed previously that drivers supporting optional muxes
> do not need to "select" MULTIPLEXER through Kconfig,
> E.g. the renesas sdhi driver.
>
> However other drivers are already selecting it even though the mux
> is optional, see e.g. phy-can-transceiver.
>
> In order to support muxes in renesas sdhi driver e.g., users must choose to
> enable both the renesas driver, and multiplexer subsystem via the
> configuration.
>
> The mux core standalone also supports a limited use-case without other
> driver
> interactions, setting idle-state e.g.:
>
> mux-controller {
>      compatible = "gpio-mux";
>      #mux-control-cells = <0>;
>      mux-gpios = <&tca6416_u20 0 GPIO_ACTIVE_HIGH>;
>      idle-state = <0>;
> };
>
> So it can be generally useful for a user to enable CONFIG_MULTIPLEXER.

Then please say so in the patch description.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v8 0/7] mmc: host: renesas_sdhi_core: support configuring an optional sdio mux

[Ulf Hansson]

On Wed, 4 Feb 2026 at 16:33, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> On Tue, 3 Feb 2026 at 14:01, Josua Mayer <josua@solid-run.com> wrote:
> >
> > Some Renesas SoC based boards mux SD and eMMC on a single sdio
> > controller, exposing user control by dip switch and software control by
> > gpio.
> >
> > Purpose is to simplify development and provisioning by selecting boot
> > media at power-on, and again before starting linux.
> >
> > Add binding and driver support for linking a (gpio) mux to renesas sdio
> > controller.
> >
> > Introduce generic helper functions for getting managed and selected
> > mux-state objects, and switch i2c-omap and phy-can-transceiver drivers.
> >
> > Signed-off-by: Josua Mayer <josua@solid-run.com>
> > ---
> > Changes in v8:
> > - Add defensive null checks for all non-optional calls to internal
> >   mux_get function.
> > - Document NULL return value on applicable functions.
> > - Avoid IS_ERR_OR_NULL and ERR_PTR(0) to disarm smatch errors.
> > - Link to v7: https://lore.kernel.org/r/20260128-rz-sdio-mux-v7-0-92ebb6da0df8@solid-run.com
> >
> > Changes in v7:
> > - picked up reviewed-tags
> > - fix Kconfig change to add the missing prompt for CONFIG_MULTIPLEXER,
> >   and enable it by default when COMPILE_TEST is set.
> >   (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
> > - fix another kernel build robot warning: undocumented C struct member
> > - Link to v6: https://lore.kernel.org/r/20260121-rz-sdio-mux-v6-0-38aa39527928@solid-run.com
> >
> > Changes in v6:
> > - replaced /* with /** for devm_mux_state_state function description.
> > - collected review tags.
> > - fixed checkpatch warnings (space-before-tab, void-return).
> >   (Reported-by: Geert Uytterhoeven)
> > - fixed use-after-free in mux core mux_get function.
> >   (Reported-by: Geert Uytterhoeven)
> > - fix mux helper error path uninitialised return code variable.
> >   (Reported-by: kernel test robot <lkp@intel.com>)
> > - Link to v5: https://lore.kernel.org/r/20260118-rz-sdio-mux-v5-0-3c37e8872683@solid-run.com
> >
> > Changes in v5:
> > - implemented automatic mux deselect for devm_*_selected.
> >   (Reported-by: Wolfram Sang <wsa+renesas@sang-engineering.com>)
> > - because of semantic changes I dropped reviewed and acks from omap-i2c
> >   patch (Andreas Kemnade / Wolfram Sang).
> > - fix invalid return value in void function for mux helper stubs
> >   (Reported-by: kernel test robot <lkp@intel.com>)
> > - Link to v4: https://lore.kernel.org/r/20251229-rz-sdio-mux-v4-0-a023e55758fe@solid-run.com
> >
> > Changes in v4:
> > - added MULTIPLEXER Kconfig help text.
> > - removed "select MULTIPLEXER" from renesas sdhi Kconfig, as it is
> >   not required for all devices using this driver.
> > - added stubs for all symbols exported by mux core.
> >   (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
> > - refactored mux core logic to silence ENOENT errors only on optional
> >   code paths, keeping error printing unchanged otherwise.
> >   (Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>)
> > - picked up various reviewed- and acked-by tags
> > - Link to v3: https://lore.kernel.org/r/20251210-rz-sdio-mux-v3-0-ca628db56d60@solid-run.com
> >
> > Changes in v3:
> > - updated omap-i2c and phy-can-transceiver to use new helpers.
> > - created generic helper functions for getting managed optional mux-state.
> >   (Reported-by: Rob Herring <robh@kernel.org>)
> > - picked up binding ack by Rob Herring.
> > - replaced use of "SDIO" with "SD/SDIO/eMMC" in binding document and
> >   commit descriptions.
> >   (Reported-by: Ulf Hansson <ulf.hansson@linaro.org>)
> > - Link to v2: https://lore.kernel.org/r/20251201-rz-sdio-mux-v2-0-bcb581b88dd7@solid-run.com
> >
> > Changes in v2:
> > - dropped mux-controller node from dt binding example
> >   (Reported-by: Conor Dooley <conor@kernel.org>
> >    Reported-by: Krzysztof Kozlowski <krzk@kernel.org>)
> > - Link to v1: https://lore.kernel.org/r/20251128-rz-sdio-mux-v1-0-1ede318d160f@solid-run.com
> >
> > ---
> > Josua Mayer (7):
> >       phy: can-transceiver: rename temporary helper function to avoid conflict
> >       mux: Add helper functions for getting optional and selected mux-state
> >       mux: add help text for MULTIPLEXER config option
> >       phy: can-transceiver: drop temporary helper getting optional mux-state
> >       i2c: omap: switch to new generic helper for getting selected mux-state
> >       dt-bindings: mmc: renesas,sdhi: Add mux-states property
> >       mmc: host: renesas_sdhi_core: support selecting an optional mux
> >
> >  .../devicetree/bindings/mmc/renesas,sdhi.yaml      |   6 +
> >  drivers/i2c/busses/i2c-omap.c                      |  24 +--
> >  drivers/mmc/host/renesas_sdhi_core.c               |   6 +
> >  drivers/mux/Kconfig                                |   8 +-
> >  drivers/mux/core.c                                 | 205 +++++++++++++++++----
> >  drivers/phy/phy-can-transceiver.c                  |  10 -
> >  include/linux/mux/consumer.h                       | 108 ++++++++++-
> >  7 files changed, 302 insertions(+), 65 deletions(-)
> > ---
> > base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> > change-id: 20251128-rz-sdio-mux-acc5137f1618
> >
> > Best regards,
> > --
> > Josua Mayer <josua@solid-run.com>
> >
> >
>
> The series applied for next, thanks!

Unfortunately my pull request for MMC for v7.0 was broken and will not
be pulled by Linus, hence I need to drop the $subject series from my
next branch.

Please submit a new version of the series when v7.0-rc1 is out and
let's fix the build errors and the dependency to the phy subsystem [1]
properly, so we can land this for v7.1 instead.

Kind regards
Uffe

[1]
https://lkml.org/lkml/2026/2/12/399 (lore was down, so pointing to
lkml.org instead)