All devices supported by simple MFD use the same 8-bit register 8-bit
value regmap configuration.  There is an option available for a device
to specify a custom configuration, but no existing device uses it.

Rather than requiring a "full" regmap configuration to be provided to
change only the max_register value, Lee Jones suggested allowing
max_register to be specified in the simple_mfd_data structure.  The
8-bit register 8-bit configuration is still used by default, but
max_register is also applied if it is non-zero.

If both regmap_config and max_register are provided, the max_register
field in the regmap_config structure is ignored.

Signed-off-by: Alex Elder <elder@riscstar.com>
Suggested-by: Lee Jones <lee@kernel.org>
---
v9: - max_register takes precedence over regmap_config in simple_mfd_data
    - New function simple_regmap_config() encapsulates providing config
    - simple_regmap_config() allocates a regmap_config if necessary
    - A small duplicated comment is removed in "simple-mfd-i2c.h"

 drivers/mfd/simple-mfd-i2c.c | 38 +++++++++++++++++++++++++++++++-----
 drivers/mfd/simple-mfd-i2c.h |  5 +----
 2 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
index 22159913bea03..f3ba79c112d4e 100644
--- a/drivers/mfd/simple-mfd-i2c.c
+++ b/drivers/mfd/simple-mfd-i2c.c
@@ -29,6 +29,36 @@ static const struct regmap_config regmap_config_8r_8v = {
 	.val_bits = 8,
 };
 
+/*
+ * Determine regmap config to use.  If no regmap_config is provided,
+ * regmap_config_8r_8v is used.  If max_register is specified it is
+ * (also) used, whether or not regmap_config is provided.
+ */
+static const struct regmap_config *
+simple_regmap_config(struct device *dev, const struct simple_mfd_data *data)
+{
+	struct regmap_config *regmap_config;
+
+	if (!data)
+		return &regmap_config_8r_8v;
+
+	if (data->regmap_config && !data->max_register)
+		return data->regmap_config;
+
+	regmap_config = devm_kzalloc(dev, sizeof(*regmap_config), GFP_KERNEL);
+	if (!regmap_config)
+		return NULL;
+
+	if (data->regmap_config)
+		*regmap_config = *data->regmap_config;
+	else
+		*regmap_config = regmap_config_8r_8v;
+	if (data->max_register)
+		regmap_config->max_register = data->max_register;
+
+	return regmap_config;
+}
+
 static int simple_mfd_i2c_probe(struct i2c_client *i2c)
 {
 	const struct simple_mfd_data *simple_mfd_data;
@@ -38,11 +68,9 @@ static int simple_mfd_i2c_probe(struct i2c_client *i2c)
 
 	simple_mfd_data = device_get_match_data(&i2c->dev);
 
-	/* If no regmap_config is specified, use the default 8reg and 8val bits */
-	if (!simple_mfd_data || !simple_mfd_data->regmap_config)
-		regmap_config = &regmap_config_8r_8v;
-	else
-		regmap_config = simple_mfd_data->regmap_config;
+	regmap_config = simple_regmap_config(&i2c->dev, simple_mfd_data);
+	if (!regmap_config)
+		return -ENOMEM;
 
 	regmap = devm_regmap_init_i2c(i2c, regmap_config);
 	if (IS_ERR(regmap))
diff --git a/drivers/mfd/simple-mfd-i2c.h b/drivers/mfd/simple-mfd-i2c.h
index 7cb2bdd347d97..6fa36b3d7a217 100644
--- a/drivers/mfd/simple-mfd-i2c.h
+++ b/drivers/mfd/simple-mfd-i2c.h
@@ -8,10 +8,6 @@
  * shared by all sub-devices.  Children can use their parent's device structure
  * (dev.parent) in order to reference it.
  *
- * This driver creates a single register map with the intention for it to be
- * shared by all sub-devices.  Children can use their parent's device structure
- * (dev.parent) in order to reference it.
- *
  * Once the register map has been successfully initialised, any sub-devices
  * represented by child nodes in Device Tree or via the MFD cells in the
  * associated C file will be subsequently registered.
@@ -25,6 +21,7 @@
 
 struct simple_mfd_data {
 	const struct regmap_config *regmap_config;
+	unsigned int max_register;
 	const struct mfd_cell *mfd_cell;
 	size_t mfd_cell_size;
 };
-- 
2.43.0

On 7/24/25 3:25 PM, Alex Elder wrote:
> All devices supported by simple MFD use the same 8-bit register 8-bit
> value regmap configuration.  There is an option available for a device
> to specify a custom configuration, but no existing device uses it.
> 
> Rather than requiring a "full" regmap configuration to be provided to
> change only the max_register value, Lee Jones suggested allowing
> max_register to be specified in the simple_mfd_data structure.  The
> 8-bit register 8-bit configuration is still used by default, but
> max_register is also applied if it is non-zero.
> 
> If both regmap_config and max_register are provided, the max_register
> field in the regmap_config structure is ignored.

It occurred to me this morning that the regmap_config structure
can be freed after the call to devm_regmap_init_i2c(), so I'm
going to add a function to free it (if it was dynamically
allocated).

					-Alex

> Signed-off-by: Alex Elder <elder@riscstar.com>
> Suggested-by: Lee Jones <lee@kernel.org>
> ---
> v9: - max_register takes precedence over regmap_config in simple_mfd_data
>      - New function simple_regmap_config() encapsulates providing config
>      - simple_regmap_config() allocates a regmap_config if necessary
>      - A small duplicated comment is removed in "simple-mfd-i2c.h"
> 
>   drivers/mfd/simple-mfd-i2c.c | 38 +++++++++++++++++++++++++++++++-----
>   drivers/mfd/simple-mfd-i2c.h |  5 +----
>   2 files changed, 34 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
> index 22159913bea03..f3ba79c112d4e 100644
> --- a/drivers/mfd/simple-mfd-i2c.c
> +++ b/drivers/mfd/simple-mfd-i2c.c
> @@ -29,6 +29,36 @@ static const struct regmap_config regmap_config_8r_8v = {
>   	.val_bits = 8,
>   };
>   
> +/*
> + * Determine regmap config to use.  If no regmap_config is provided,
> + * regmap_config_8r_8v is used.  If max_register is specified it is
> + * (also) used, whether or not regmap_config is provided.
> + */
> +static const struct regmap_config *
> +simple_regmap_config(struct device *dev, const struct simple_mfd_data *data)
> +{
> +	struct regmap_config *regmap_config;
> +
> +	if (!data)
> +		return &regmap_config_8r_8v;
> +
> +	if (data->regmap_config && !data->max_register)
> +		return data->regmap_config;
> +
> +	regmap_config = devm_kzalloc(dev, sizeof(*regmap_config), GFP_KERNEL);
> +	if (!regmap_config)
> +		return NULL;
> +
> +	if (data->regmap_config)
> +		*regmap_config = *data->regmap_config;
> +	else
> +		*regmap_config = regmap_config_8r_8v;
> +	if (data->max_register)
> +		regmap_config->max_register = data->max_register;
> +
> +	return regmap_config;
> +}
> +
>   static int simple_mfd_i2c_probe(struct i2c_client *i2c)
>   {
>   	const struct simple_mfd_data *simple_mfd_data;
> @@ -38,11 +68,9 @@ static int simple_mfd_i2c_probe(struct i2c_client *i2c)
>   
>   	simple_mfd_data = device_get_match_data(&i2c->dev);
>   
> -	/* If no regmap_config is specified, use the default 8reg and 8val bits */
> -	if (!simple_mfd_data || !simple_mfd_data->regmap_config)
> -		regmap_config = &regmap_config_8r_8v;
> -	else
> -		regmap_config = simple_mfd_data->regmap_config;
> +	regmap_config = simple_regmap_config(&i2c->dev, simple_mfd_data);
> +	if (!regmap_config)
> +		return -ENOMEM;
>   
>   	regmap = devm_regmap_init_i2c(i2c, regmap_config);
>   	if (IS_ERR(regmap))
> diff --git a/drivers/mfd/simple-mfd-i2c.h b/drivers/mfd/simple-mfd-i2c.h
> index 7cb2bdd347d97..6fa36b3d7a217 100644
> --- a/drivers/mfd/simple-mfd-i2c.h
> +++ b/drivers/mfd/simple-mfd-i2c.h
> @@ -8,10 +8,6 @@
>    * shared by all sub-devices.  Children can use their parent's device structure
>    * (dev.parent) in order to reference it.
>    *
> - * This driver creates a single register map with the intention for it to be
> - * shared by all sub-devices.  Children can use their parent's device structure
> - * (dev.parent) in order to reference it.
> - *
>    * Once the register map has been successfully initialised, any sub-devices
>    * represented by child nodes in Device Tree or via the MFD cells in the
>    * associated C file will be subsequently registered.
> @@ -25,6 +21,7 @@
>   
>   struct simple_mfd_data {
>   	const struct regmap_config *regmap_config;
> +	unsigned int max_register;
>   	const struct mfd_cell *mfd_cell;
>   	size_t mfd_cell_size;
>   };