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 specify a "full" regmap configuration to change only
the max_register value, Lee Jones suggested allowing max_register
to be specified in the simple_mfd_data structure.  If regmap_config
and max_register are both supplied, the max_register field is ignored.

Signed-off-by: Alex Elder <elder@riscstar.com>
Suggested-by: Lee Jones <lee@kernel.org>
---
v8: - Use regmap_config_8r_8v, modifying it if max_register supplied

 drivers/mfd/simple-mfd-i2c.c | 8 ++++++--
 drivers/mfd/simple-mfd-i2c.h | 3 ++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
index 22159913bea03..5138aa72140b5 100644
--- a/drivers/mfd/simple-mfd-i2c.c
+++ b/drivers/mfd/simple-mfd-i2c.c
@@ -24,15 +24,16 @@
 
 #include "simple-mfd-i2c.h"
 
-static const struct regmap_config regmap_config_8r_8v = {
+static struct regmap_config regmap_config_8r_8v = {
 	.reg_bits = 8,
 	.val_bits = 8,
+	/* .max_register can be specified in simple_mfd_data */
 };
 
 static int simple_mfd_i2c_probe(struct i2c_client *i2c)
 {
 	const struct simple_mfd_data *simple_mfd_data;
-	const struct regmap_config *regmap_config;
+	struct regmap_config *regmap_config;
 	struct regmap *regmap;
 	int ret;
 
@@ -43,8 +44,11 @@ static int simple_mfd_i2c_probe(struct i2c_client *i2c)
 		regmap_config = &regmap_config_8r_8v;
 	else
 		regmap_config = simple_mfd_data->regmap_config;
+	if (simple_mfd_data && !simple_mfd_data->regmap_config)
+		regmap_config->max_register = simple_mfd_data->max_register;
 
 	regmap = devm_regmap_init_i2c(i2c, regmap_config);
+	regmap_config->max_register = 0;
 	if (IS_ERR(regmap))
 		return PTR_ERR(regmap);
 
diff --git a/drivers/mfd/simple-mfd-i2c.h b/drivers/mfd/simple-mfd-i2c.h
index 7cb2bdd347d97..ea2a96af8bce4 100644
--- a/drivers/mfd/simple-mfd-i2c.h
+++ b/drivers/mfd/simple-mfd-i2c.h
@@ -24,7 +24,8 @@
 #include <linux/regmap.h>
 
 struct simple_mfd_data {
-	const struct regmap_config *regmap_config;
+	struct regmap_config *regmap_config;
+	unsigned int max_register;	/* Ignored if regmap_config supplied */
 	const struct mfd_cell *mfd_cell;
 	size_t mfd_cell_size;
 };
-- 
2.45.2

On Thu, 10 Jul 2025, 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 specify a "full" regmap configuration to change only
> the max_register value, Lee Jones suggested allowing max_register
> to be specified in the simple_mfd_data structure.  If regmap_config
> and max_register are both supplied, the max_register field is ignored.
> 
> Signed-off-by: Alex Elder <elder@riscstar.com>
> Suggested-by: Lee Jones <lee@kernel.org>
> ---
> v8: - Use regmap_config_8r_8v, modifying it if max_register supplied
> 
>  drivers/mfd/simple-mfd-i2c.c | 8 ++++++--
>  drivers/mfd/simple-mfd-i2c.h | 3 ++-
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
> index 22159913bea03..5138aa72140b5 100644
> --- a/drivers/mfd/simple-mfd-i2c.c
> +++ b/drivers/mfd/simple-mfd-i2c.c
> @@ -24,15 +24,16 @@
>  
>  #include "simple-mfd-i2c.h"
>  
> -static const struct regmap_config regmap_config_8r_8v = {
> +static struct regmap_config regmap_config_8r_8v = {
>  	.reg_bits = 8,
>  	.val_bits = 8,
> +	/* .max_register can be specified in simple_mfd_data */

Drop this comment please.

>  };
>  
>  static int simple_mfd_i2c_probe(struct i2c_client *i2c)
>  {
>  	const struct simple_mfd_data *simple_mfd_data;
> -	const struct regmap_config *regmap_config;
> +	struct regmap_config *regmap_config;
>  	struct regmap *regmap;
>  	int ret;
>  
> @@ -43,8 +44,11 @@ static int simple_mfd_i2c_probe(struct i2c_client *i2c)
>  		regmap_config = &regmap_config_8r_8v;
>  	else
>  		regmap_config = simple_mfd_data->regmap_config;
> +	if (simple_mfd_data && !simple_mfd_data->regmap_config)
> +		regmap_config->max_register = simple_mfd_data->max_register;

If max_register is set in simple_mfd_data, it should take precedence.

if (simple_mfd_data && simple_mfd_data->max_register)
	regmap_config->max_register = simple_mfd_data->max_register;

>  	regmap = devm_regmap_init_i2c(i2c, regmap_config);
> +	regmap_config->max_register = 0;

Does max_register definitely have persistence over subsequent calls?

>  	if (IS_ERR(regmap))
>  		return PTR_ERR(regmap);
>  
> diff --git a/drivers/mfd/simple-mfd-i2c.h b/drivers/mfd/simple-mfd-i2c.h
> index 7cb2bdd347d97..ea2a96af8bce4 100644
> --- a/drivers/mfd/simple-mfd-i2c.h
> +++ b/drivers/mfd/simple-mfd-i2c.h
> @@ -24,7 +24,8 @@
>  #include <linux/regmap.h>
>  
>  struct simple_mfd_data {
> -	const struct regmap_config *regmap_config;
> +	struct regmap_config *regmap_config;
> +	unsigned int max_register;	/* Ignored if regmap_config supplied */
>  	const struct mfd_cell *mfd_cell;
>  	size_t mfd_cell_size;
>  };
> -- 
> 2.45.2
> 

-- 
Lee Jones [李琼斯]

On 7/23/25 4:51 AM, Lee Jones wrote:
> On Thu, 10 Jul 2025, 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 specify a "full" regmap configuration to change only
>> the max_register value, Lee Jones suggested allowing max_register
>> to be specified in the simple_mfd_data structure.  If regmap_config
>> and max_register are both supplied, the max_register field is ignored.
>>
>> Signed-off-by: Alex Elder <elder@riscstar.com>
>> Suggested-by: Lee Jones <lee@kernel.org>
>> ---
>> v8: - Use regmap_config_8r_8v, modifying it if max_register supplied
>>
>>   drivers/mfd/simple-mfd-i2c.c | 8 ++++++--
>>   drivers/mfd/simple-mfd-i2c.h | 3 ++-
>>   2 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
>> index 22159913bea03..5138aa72140b5 100644
>> --- a/drivers/mfd/simple-mfd-i2c.c
>> +++ b/drivers/mfd/simple-mfd-i2c.c
>> @@ -24,15 +24,16 @@
>>   
>>   #include "simple-mfd-i2c.h"
>>   
>> -static const struct regmap_config regmap_config_8r_8v = {
>> +static struct regmap_config regmap_config_8r_8v = {
>>   	.reg_bits = 8,
>>   	.val_bits = 8,
>> +	/* .max_register can be specified in simple_mfd_data */
> 
> Drop this comment please.
> 
>>   };
>>   
>>   static int simple_mfd_i2c_probe(struct i2c_client *i2c)
>>   {
>>   	const struct simple_mfd_data *simple_mfd_data;
>> -	const struct regmap_config *regmap_config;
>> +	struct regmap_config *regmap_config;
>>   	struct regmap *regmap;
>>   	int ret;
>>   
>> @@ -43,8 +44,11 @@ static int simple_mfd_i2c_probe(struct i2c_client *i2c)
>>   		regmap_config = &regmap_config_8r_8v;
>>   	else
>>   		regmap_config = simple_mfd_data->regmap_config;
>> +	if (simple_mfd_data && !simple_mfd_data->regmap_config)
>> +		regmap_config->max_register = simple_mfd_data->max_register;
> 
> If max_register is set in simple_mfd_data, it should take precedence.

I don't really agree with that.  If simple_mfd_data->regmap_config
is provided, why not use the max_register field already available
there?

This is why I said above that I think this feature doesn't add
much value.  It provides a second way to specify something, but
in the end it complicates the code more than it's worth.

The only time this new simple_mfd_data->max_register field seems
to make sense is if it were the only thing provided (without
simple_mfd_data->regmap_config being supplied).  In that case,
I see the benefit--a null simple_mfd_data->regmap_config means
use regmap_config_8r_8v, and overlay it with the max_register
value.  The new max_register field avoids defining another huge
but mostly empty regmap_config structure.

Anyway, back to your original point:  I said in v7 "If both
are specified, the max_register value is ignored" and I think
that's the simplest.  Specify one or the other--if you want
to define things in regmap_config, then that's where you add
your max_register.  If you like regmap_config_8r_8v but want
to define a max_register value, just provide max_register.

If you insist, I'll do what you say but before I sent another
version I wanted to explain my reasoning.


> if (simple_mfd_data && simple_mfd_data->max_register)
> 	regmap_config->max_register = simple_mfd_data->max_register;
> 
>>   	regmap = devm_regmap_init_i2c(i2c, regmap_config);
>> +	regmap_config->max_register = 0;
> 
> Does max_register definitely have persistence over subsequent calls?

It is a global variable.  Isn't that how they work?  When
it was read-only there was no concern about that, nor about
any possible concurrent access (though I don't think multiple
probes can be using this code at once).

We could allocate a new one each time instead.

I think what I offered in v5 was acceptable.  If you're
willing to accept that I will be happy to keep discussing
(and implementing) the max_register feature.

					-Alex

> 
>>   	if (IS_ERR(regmap))
>>   		return PTR_ERR(regmap);
>>   
>> diff --git a/drivers/mfd/simple-mfd-i2c.h b/drivers/mfd/simple-mfd-i2c.h
>> index 7cb2bdd347d97..ea2a96af8bce4 100644
>> --- a/drivers/mfd/simple-mfd-i2c.h
>> +++ b/drivers/mfd/simple-mfd-i2c.h
>> @@ -24,7 +24,8 @@
>>   #include <linux/regmap.h>
>>   
>>   struct simple_mfd_data {
>> -	const struct regmap_config *regmap_config;
>> +	struct regmap_config *regmap_config;
>> +	unsigned int max_register;	/* Ignored if regmap_config supplied */
>>   	const struct mfd_cell *mfd_cell;
>>   	size_t mfd_cell_size;
>>   };
>> -- 
>> 2.45.2
>>
>

On Wed, 23 Jul 2025, Alex Elder wrote:

> On 7/23/25 4:51 AM, Lee Jones wrote:
> > On Thu, 10 Jul 2025, 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 specify a "full" regmap configuration to change only
> > > the max_register value, Lee Jones suggested allowing max_register
> > > to be specified in the simple_mfd_data structure.  If regmap_config
> > > and max_register are both supplied, the max_register field is ignored.
> > > 
> > > Signed-off-by: Alex Elder <elder@riscstar.com>
> > > Suggested-by: Lee Jones <lee@kernel.org>
> > > ---
> > > v8: - Use regmap_config_8r_8v, modifying it if max_register supplied
> > > 
> > >   drivers/mfd/simple-mfd-i2c.c | 8 ++++++--
> > >   drivers/mfd/simple-mfd-i2c.h | 3 ++-
> > >   2 files changed, 8 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
> > > index 22159913bea03..5138aa72140b5 100644
> > > --- a/drivers/mfd/simple-mfd-i2c.c
> > > +++ b/drivers/mfd/simple-mfd-i2c.c
> > > @@ -24,15 +24,16 @@
> > >   #include "simple-mfd-i2c.h"
> > > -static const struct regmap_config regmap_config_8r_8v = {
> > > +static struct regmap_config regmap_config_8r_8v = {
> > >   	.reg_bits = 8,
> > >   	.val_bits = 8,
> > > +	/* .max_register can be specified in simple_mfd_data */
> > 
> > Drop this comment please.
> > 
> > >   };
> > >   static int simple_mfd_i2c_probe(struct i2c_client *i2c)
> > >   {
> > >   	const struct simple_mfd_data *simple_mfd_data;
> > > -	const struct regmap_config *regmap_config;
> > > +	struct regmap_config *regmap_config;
> > >   	struct regmap *regmap;
> > >   	int ret;
> > > @@ -43,8 +44,11 @@ static int simple_mfd_i2c_probe(struct i2c_client *i2c)
> > >   		regmap_config = &regmap_config_8r_8v;
> > >   	else
> > >   		regmap_config = simple_mfd_data->regmap_config;
> > > +	if (simple_mfd_data && !simple_mfd_data->regmap_config)
> > > +		regmap_config->max_register = simple_mfd_data->max_register;
> > 
> > If max_register is set in simple_mfd_data, it should take precedence.
> 
> I don't really agree with that.  If simple_mfd_data->regmap_config
> is provided, why not use the max_register field already available
> there?

Why would a user add a max_register override to simple_mfd_data if they
didn't want to use it?

> This is why I said above that I think this feature doesn't add
> much value.  It provides a second way to specify something, but
> in the end it complicates the code more than it's worth.
> 
> The only time this new simple_mfd_data->max_register field seems
> to make sense is if it were the only thing provided (without
> simple_mfd_data->regmap_config being supplied).  In that case,
> I see the benefit--a null simple_mfd_data->regmap_config means
> use regmap_config_8r_8v, and overlay it with the max_register
> value.  The new max_register field avoids defining another huge
> but mostly empty regmap_config structure.

This is your use-case, right?

> Anyway, back to your original point:  I said in v7 "If both
> are specified, the max_register value is ignored" and I think
> that's the simplest.  Specify one or the other--if you want
> to define things in regmap_config, then that's where you add
> your max_register.  If you like regmap_config_8r_8v but want
> to define a max_register value, just provide max_register.
> 
> If you insist, I'll do what you say but before I sent another
> version I wanted to explain my reasoning.

I hear you and I get what you're saying.

I see no use-case where a user would provide both regmap_config AND
max_register either.  However, I see max_register in simple_mfd_data as
an override, so I would like it to take precedence please.

> > if (simple_mfd_data && simple_mfd_data->max_register)
> > 	regmap_config->max_register = simple_mfd_data->max_register;
> > 
> > >   	regmap = devm_regmap_init_i2c(i2c, regmap_config);
> > > +	regmap_config->max_register = 0;
> > 
> > Does max_register definitely have persistence over subsequent calls?
> 
> It is a global variable.  Isn't that how they work?  When
> it was read-only there was no concern about that, nor about
> any possible concurrent access (though I don't think multiple
> probes can be using this code at once).
> 
> We could allocate a new one each time instead.
> 
> I think what I offered in v5 was acceptable.  If you're
> willing to accept that I will be happy to keep discussing
> (and implementing) the max_register feature.

Yes, I'm inclined to agree.

Make the call and I will respect your decision.

-- 
Lee Jones [李琼斯]