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

From: Lee Jones <lee.jones@linaro.org>
To: Michael Walle <michael@walle.cc>
Cc: devicetree@vger.kernel.org, arnd@arndb.de,
	gregkh@linuxfoundation.org, linus.walleij@linaro.org,
	linux-kernel@vger.kernel.org, robh+dt@kernel.org,
	bgolaszewski@baylibre.com, broonie@kernel.org,
	andriy.shevchenko@linux.intel.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 1/1] mfd: Add I2C based System Configuaration (SYSCON) access
Date: Thu, 2 Jul 2020 08:14:02 +0100	[thread overview]
Message-ID: <20200702071402.GP1179328@dell> (raw)
In-Reply-To: <e436fd60bf0ebb6d72a76034d0fc35de@walle.cc>

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@linaro.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.

What is your use-case?  This is set-up for based I2C drivers to call
into.  'client' is given to them as their .probe() arg.

> 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?

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog

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