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 <redacted>
---
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.

-michael