linux-kernel - Re: [PATCH v9 2/8] mfd: simple-mfd-i2c: specify max

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Message-ID: <e236fa5e-7085-419e-bc68-c49f9416847b@riscstar.com>
Date: Fri, 25 Jul 2025 07:27:27 -0500
From: Alex Elder <elder@...cstar.com>
To: lee@...nel.org, lgirdwood@...il.com, broonie@...nel.org,
 alexandre.belloni@...tlin.com, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org
Cc: mat.jonczyk@...pl, dlan@...too.org, paul.walmsley@...ive.com,
 palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr,
 linux.amoon@...il.com, troymitchell988@...il.com, guodong@...cstar.com,
 linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
 linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 2/8] mfd: simple-mfd-i2c: specify max_register

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@...cstar.com>
> Suggested-by: Lee Jones <lee@...nel.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;
>   };