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

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Date:   Tue, 30 Jun 2020 11:16:33 +0200
From:   Michael Walle <michael@...le.cc>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     robh+dt@...nel.org, broonie@...nel.org, gregkh@...uxfoundation.org,
        andriy.shevchenko@...ux.intel.com, devicetree@...r.kernel.org,
        linus.walleij@...aro.org, bgolaszewski@...libre.com, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/1] mfd: Add I2C based System Configuaration (SYSCON)
 access

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@...aro.org>
> ---
> 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