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

[Michael Walle]

Am 2020-07-01 09:04, schrieb Lee Jones:
> On Wed, 01 Jul 2020, Michael Walle wrote:
>
> > 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>;
> >     };
> >   };
> > };
>
> Yes, that was the idea.
>
> > But I think the childen are not enumerated if its an I2C device. And
> > the actual i2c driver is also missing.
>
> What do you mean?  Can you elaborate?

There is no i2c_driver instance who would create the regmap. If I'm
reading the I2C code correctly, it won't probe any i2c device of a
bus if there is no i2c_driver with an associated .probe() or
.probe_new(). And even if it is probed, its subnodes won't be
enumerated; the "simple-mfd" code only works for MMIO busses, right?
Or I'm getting something really wrong here..

-michael