The status of each mux is read during suspend and stored in the private
memory of the mux_chip.
Then the state is restored during the resume.

Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
---
In this second version, as discussed with Peter, everything is done in the
mmio-mux driver.
A mux_mmio_set() function was added, and used during suspend stage to get
the status of the of the muxes.
This status is stored in the private memory of the mux_chip.
---
Changes in v2:
- Remove all modifications done in the mux subsystem
- Add a mux_mmio_set()
- Read the status of muxes during suspend and store in the private memory
  of the mux_chip.
- Use this status to restore muxes during resume.
- Link to v1: https://lore.kernel.org/r/20240613-mux-mmio-resume-support-v1-0-4525bf56024a@bootlin.com
---
 drivers/mux/mmio.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 73 insertions(+), 9 deletions(-)

diff --git a/drivers/mux/mmio.c b/drivers/mux/mmio.c
index 30a952c34365..30b84382637f 100644
--- a/drivers/mux/mmio.c
+++ b/drivers/mux/mmio.c
@@ -15,11 +15,25 @@
 #include <linux/property.h>
 #include <linux/regmap.h>
 
+struct mux_mmio {
+	struct regmap_field **fields;
+	unsigned int *hardware_states;
+};
+
+static int mux_mmio_get(struct mux_control *mux, int *state)
+{
+	struct mux_mmio *mux_mmio = mux_chip_priv(mux->chip);
+	unsigned int index = mux_control_get_index(mux);
+
+	return regmap_field_read(mux_mmio->fields[index], state);
+}
+
 static int mux_mmio_set(struct mux_control *mux, int state)
 {
-	struct regmap_field **fields = mux_chip_priv(mux->chip);
+	struct mux_mmio *mux_mmio = mux_chip_priv(mux->chip);
+	unsigned int index = mux_control_get_index(mux);
 
-	return regmap_field_write(fields[mux_control_get_index(mux)], state);
+	return regmap_field_write(mux_mmio->fields[index], state);
 }
 
 static const struct mux_control_ops mux_mmio_ops = {
@@ -37,8 +51,8 @@ static int mux_mmio_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct device_node *np = dev->of_node;
-	struct regmap_field **fields;
 	struct mux_chip *mux_chip;
+	struct mux_mmio *mux_mmio;
 	struct regmap *regmap;
 	int num_fields;
 	int ret;
@@ -69,12 +83,20 @@ static int mux_mmio_probe(struct platform_device *pdev)
 	}
 	num_fields = ret / 2;
 
-	mux_chip = devm_mux_chip_alloc(dev, num_fields, num_fields *
-				       sizeof(*fields));
+	mux_chip = devm_mux_chip_alloc(dev, num_fields, sizeof(struct mux_mmio));
 	if (IS_ERR(mux_chip))
 		return PTR_ERR(mux_chip);
 
-	fields = mux_chip_priv(mux_chip);
+	mux_mmio = mux_chip_priv(mux_chip);
+
+	mux_mmio->fields = devm_kmalloc(dev, num_fields * sizeof(*mux_mmio->fields), GFP_KERNEL);
+	if (IS_ERR(mux_mmio->fields))
+		return PTR_ERR(mux_mmio->fields);
+
+	mux_mmio->hardware_states = devm_kmalloc(dev, num_fields *
+						 sizeof(*mux_mmio->hardware_states), GFP_KERNEL);
+	if (IS_ERR(mux_mmio->hardware_states))
+		return PTR_ERR(mux_mmio->hardware_states);
 
 	for (i = 0; i < num_fields; i++) {
 		struct mux_control *mux = &mux_chip->mux[i];
@@ -104,9 +126,9 @@ static int mux_mmio_probe(struct platform_device *pdev)
 			return -EINVAL;
 		}
 
-		fields[i] = devm_regmap_field_alloc(dev, regmap, field);
-		if (IS_ERR(fields[i])) {
-			ret = PTR_ERR(fields[i]);
+		mux_mmio->fields[i] = devm_regmap_field_alloc(dev, regmap, field);
+		if (IS_ERR(mux_mmio->fields[i])) {
+			ret = PTR_ERR(mux_mmio->fields[i]);
 			dev_err(dev, "bitfield %d: failed allocate: %d\n",
 				i, ret);
 			return ret;
@@ -130,13 +152,55 @@ static int mux_mmio_probe(struct platform_device *pdev)
 
 	mux_chip->ops = &mux_mmio_ops;
 
+	dev_set_drvdata(dev, mux_chip);
+
 	return devm_mux_chip_register(dev, mux_chip);
 }
 
+static int mux_mmio_suspend_noirq(struct device *dev)
+{
+	struct mux_chip *mux_chip = dev_get_drvdata(dev);
+	struct mux_mmio *mux_mmio = mux_chip_priv(mux_chip);
+	unsigned int state;
+	int ret, i;
+
+	for (i = 0; i < mux_chip->controllers; i++) {
+		ret = mux_mmio_get(&mux_chip->mux[i], &state);
+		if (ret) {
+			dev_err(dev, "control %u: error saving mux: %d\n", i, ret);
+			return ret;
+		}
+
+		mux_mmio->hardware_states[i] = state;
+	}
+
+	return 0;
+}
+
+static int mux_mmio_resume_noirq(struct device *dev)
+{
+	struct mux_chip *mux_chip = dev_get_drvdata(dev);
+	struct mux_mmio *mux_mmio = mux_chip_priv(mux_chip);
+	int ret, i;
+
+	for (i = 0; i < mux_chip->controllers; i++) {
+		ret = mux_mmio_set(&mux_chip->mux[i], mux_mmio->hardware_states[i]);
+		if (ret) {
+			dev_err(dev, "control %u: error restoring mux: %d\n", i, ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static DEFINE_NOIRQ_DEV_PM_OPS(mux_mmio_pm_ops, mux_mmio_suspend_noirq, mux_mmio_resume_noirq);
+
 static struct platform_driver mux_mmio_driver = {
 	.driver = {
 		.name = "mmio-mux",
 		.of_match_table	= mux_mmio_dt_ids,
+		.pm = pm_sleep_ptr(&mux_mmio_pm_ops),
 	},
 	.probe = mux_mmio_probe,
 };

---
base-commit: caf614bf68351c7e9e38dd37e07539417c757813
change-id: 20240613-mux-mmio-resume-support-4f3b2a34a32a

Best regards,
-- 
Thomas Richard <thomas.richard@bootlin.com>

On 9/11/24 10:53, Thomas Richard wrote:
> The status of each mux is read during suspend and stored in the private
> memory of the mux_chip.
> Then the state is restored during the resume.

Hello Peter,

Did you have time to look at this patch ?

Regards,

Thomas