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

[Michael Walle]

Am 2020-07-02 09:14, schrieb Lee Jones:
> On Tue, 30 Jun 2020, Michael Walle wrote:
>
> > Hi Lee,
> >
> > 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.
>
> What is your use-case?

Still my sl28 mfd driver. There the sub devices just need a regmap.

>  This is set-up for based I2C drivers to call
> into.  'client' is given to them as their .probe() arg.

Ok, I see. Then this doesn't fit.

-michael

> > 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.
>
> This is a helper for I2C clients.  There aren't any OF helpers in here
> (yet).  If you think they would be helpful we can add them.  How do
> you see them being used?