Re: [PATCH v4 1/1] mfd: Add I2C based System Configuaration (SYSCON) access

[Michael Walle]

Hi Lee,

Am 2020-06-30 11:16, schrieb Michael Walle:
> I'm just trying to use this for my sl28 driver. Some remarks, see 
> below.
>
> Am 2020-06-22 09:51, schrieb Lee Jones:
> > The existing SYSCON implementation only supports MMIO (memory mapped)
> > accesses, facilitated by Regmap.  This extends support for registers
> > held behind I2C busses.
> >
> > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > ---
> > Changelog:
> >
> > v3 => v4
> >   - Add ability to provide a non-default Regmap configuration
> >
> > v2 => v3
> >   - Change 'is CONFIG' present check to include loadable modules
> >     - s/#ifdef CONFIG_MFD_SYSCON_I2C/#if 
> > IS_ENABLED(CONFIG_MFD_SYSCON_I2C)/
> >
> > v1 => v2
> >   - Remove legacy references to OF
> >   - Allow building as a module (fixes h8300 0-day issue)
> >
> > drivers/mfd/Kconfig            |   7 +++
> >  drivers/mfd/Makefile           |   1 +
> >  drivers/mfd/syscon-i2c.c       | 104 
> > +++++++++++++++++++++++++++++++++
> >  include/linux/mfd/syscon-i2c.h |  36 ++++++++++++
> >  4 files changed, 148 insertions(+)
> >  create mode 100644 drivers/mfd/syscon-i2c.c
> >  create mode 100644 include/linux/mfd/syscon-i2c.h
>
> [..]
>
> > +static struct regmap *syscon_i2c_get_regmap(struct i2c_client 
> > *client,
> > +					    struct regmap_config *regmap_config)
> > +{
> > +	struct device *dev = &client->dev;
> > +	struct syscon *entry, *syscon = NULL;
> > +
> > +	spin_lock(&syscon_i2c_list_slock);
> > +
> > +	list_for_each_entry(entry, &syscon_i2c_list, list)
> > +		if (entry->dev == dev) {
> > +			syscon = entry;
> > +			break;
> > +		}
> > +
> > +	spin_unlock(&syscon_i2c_list_slock);
> > +
> > +	if (!syscon)
> > +		syscon = syscon_i2c_register(client, regmap_config);
> > +
> > +	if (IS_ERR(syscon))
> > +		return ERR_CAST(syscon);
> > +
> > +	return syscon->regmap;
> > +}
> > +
> > +struct regmap *syscon_i2c_to_regmap_config(struct i2c_client *client,
> > +					   struct regmap_config *regmap_config)
> > +{
> > +	return syscon_i2c_get_regmap(client, regmap_config);
> > +}
> > +EXPORT_SYMBOL_GPL(syscon_i2c_to_regmap_config);
> > +
> > +struct regmap *syscon_i2c_to_regmap(struct i2c_client *client)
> > +{
> > +	return syscon_i2c_get_regmap(client, &syscon_i2c_regmap_config);
> > +}
> > +EXPORT_SYMBOL_GPL(syscon_i2c_to_regmap);
>
> What do you think about
>
> struct regmap *syscon_i2c_to_regmap(struct device *dev)
> {
> 	struct i2c_client *client = i2c_verify_client(dev);
>
> 	if (!client)
> 		return ERR_PTR(-EINVAL);
>
> 	return syscon_i2c_get_regmap(client, &syscon_i2c_regmap_config);
> }
>
> Or even move it to syscon_i2c_get_regmap().
>
> This way, (a) a driver doesn't have to use "#include <linux/i2c.h>" 
> just
> to call to_i2c_client() (or i2c_verify_client()) and (b) you won't do 
> it
> all over again in all sub drivers.
>
> So you could just do a
>   regmap = syscon_i2c_to_regmap(pdev->dev.parent);
>
> I've also noticed that the mmio syscon uses device_node as parameter. 
> What
> was the reason to divert from that? Just curious.

How is this supposed to be used?

I had something like the following in mind:

&i2c {
  cpld@4a {
    compatible = "simple-mfd";
    reg = <0x4a>;

    gpio@4 {
      compatible = "vendor,gpio";
      reg = <0x4>;
    };
  };
};

But I think the childen are not enumerated if its an I2C device. And
the actual i2c driver is also missing.

-michael