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Date:   Mon, 24 Sep 2018 22:37:14 +0800
From:   Song Qiang <songqiang1304521@gmail.com>
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net,
        robh+dt@kernel.org, mark.rutland@arm.com,
        linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iio: magnetometer: Add support for PNI RM3100 9-axis
 magnetometer
Message-ID: <20180924143714.GA16236@Eros>
References: <20180920131340.6699-1-songqiang1304521@gmail.com>
 <20180922111409.597126fd@archlinux>
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On Sat, Sep 22, 2018 at 11:14:09AM +0100, Jonathan Cameron wrote:
> On Thu, 20 Sep 2018 21:13:40 +0800
> Song Qiang <songqiang1304521@gmail.com> wrote:
> 
> > PNI RM3100 magnetometer is a high resolution, large signal immunity
> > magnetometer, composed of 3 single sensors and a processing chip.
> > PNI is currently not in the vendors list, so this is also adding it.
> > 
> > Following functions are available:
> >  - Single-shot measurement from
> >    /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
> >  - Triggerd buffer measurement.
> >  - Both i2c and spi interface are supported.
> >  - Both interrupt and polling measurement is supported, depands on if
> >    the 'interrupts' in DT is declared.
> > 
> > Signed-off-by: Song Qiang <songqiang1304521@gmail.com>
> Hi Song,

...

> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	/* 3sec more wait time. */
> > +	ret = regmap_read(data->regmap, RM_REG_TMRC, &tmp);
> > +	data->conversion_time = rm3100_samp_rates[tmp-RM_TMRC_OFFSET][2] + 3000;
> > +
> > +	/* Starting all channels' conversion. */
> > +	ret = regmap_write(regmap, RM_REG_CMM,
> > +		RM_CMM_PMX | RM_CMM_PMY | RM_CMM_PMZ | RM_CMM_START);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return devm_iio_device_register(dev, indio_dev);
> Nope.  Can't do this without having a race condition.   You need
> to ensure the userspace and in kernel interfaces are removed 'before'.
> you do that RM_REG_CMM write in remove.
> 
> One option is to use devm_add_action to add a custom unwind function
> to the automatic handling. The other is to not use devm for everything 
> after the write above and do the device_unregister manually.
> 

Hi Jonathan,

I considered the both options you mentioned, and I was going to use the
manual way. But then something came to my mind, what if there is another
devm_* operation needs care, what if more. I checked devm_add_action in
source code, and it says that this function only adds unwinding handlers.
I guess this method was designed for this situation, and if we have
already used devm_ in our code, it's better to use devm_add_action for
cleanup, is that right?

yours,
Song Qiang

> > +}
> > +EXPORT_SYMBOL(rm3100_common_probe);
> > +
> > +int rm3100_common_remove(struct device *dev)
> > +{
> > +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> > +	struct rm3100_data *data = iio_priv(indio_dev);
> > +	struct regmap *regmap = data->regmap;
> > +
> > +	regmap_write(regmap, RM_REG_CMM, 0x00);
> > +
> > +	return 0;
> No real point in returning int if you are always going to put 0 in
> in it.  Should probably check the regmap_write though and output
> a log message if it fails (as no other way of telling).
> 
> > +}
> > +EXPORT_SYMBOL(rm3100_common_remove);
> > +
> > +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> > +MODULE_DESCRIPTION("PNI RM3100 9-axis magnetometer i2c driver");
> > +MODULE_LICENSE("GPL v2");
> > diff --git a/drivers/iio/magnetometer/rm3100-i2c.c b/drivers/iio/magnetometer/rm3100-i2c.c
> > new file mode 100644
> > index 000000000000..b50dc5b1b30b
> > --- /dev/null
> > +++ b/drivers/iio/magnetometer/rm3100-i2c.c
> > @@ -0,0 +1,66 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Support for PNI RM3100 9-axis geomagnetic sensor a i2c bus.
> > + *
> > + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> > + *
> > + * User Manual available at
> > + * <https://www.pnicorp.com/download/rm3100-user-manual/>
> > + *
> > + * i2c slave address 0x20 + SA1 << 1 + SA0.
> > + */
> > +
> > +#include <linux/i2c.h>
> > +
> > +#include "rm3100.h"
> > +
> > +static const struct regmap_config rm3100_regmap_config = {
> > +		.reg_bits = 8,
> This indenting seems an extra tab on conventional choice...
> > +		.val_bits = 8,
> > +
> > +		.rd_table = &rm3100_readable_table,
> > +		.wr_table = &rm3100_writable_table,
> > +		.volatile_table = &rm3100_volatile_table,
> > +
> > +		.cache_type = REGCACHE_RBTREE,
> > +};
> > +
> > +static int rm3100_probe(struct i2c_client *client)
> > +{
> > +	struct regmap *regmap;
> > +
> > +	if (!i2c_check_functionality(client->adapter,
> > +		I2C_FUNC_SMBUS_READ_I2C_BLOCK | I2C_FUNC_SMBUS_BYTE_DATA))
> > +		return -EOPNOTSUPP;
> > +
> > +	regmap =  devm_regmap_init_i2c(client, &rm3100_regmap_config);
> > +	if (IS_ERR(regmap))
> > +		return PTR_ERR(regmap);
> > +
> > +	return rm3100_common_probe(&client->dev, regmap, client->irq);
> > +}
> > +
> > +static int rm3100_remove(struct i2c_client *client)
> > +{
> > +	return rm3100_common_remove(&client->dev);
> > +}
> > +
> > +static const struct of_device_id rm3100_dt_match[] = {
> > +	{ .compatible = "pni,rm3100-i2c", },
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> > +
> > +static struct i2c_driver rm3100_driver = {
> > +	.driver = {
> > +		.name = "rm3100-i2c",
> > +		.of_match_table = rm3100_dt_match,
> > +	},
> > +	.probe_new = rm3100_probe,
> > +	.remove = rm3100_remove,
> > +};
> > +module_i2c_driver(rm3100_driver);
> > +
> > +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> > +MODULE_DESCRIPTION("PNI RM3100 9-axis magnetometer i2c driver");
> > +MODULE_LICENSE("GPL v2");
> > diff --git a/drivers/iio/magnetometer/rm3100-spi.c b/drivers/iio/magnetometer/rm3100-spi.c
> > new file mode 100644
> > index 000000000000..2c7dd9e3a1a2
> > --- /dev/null
> > +++ b/drivers/iio/magnetometer/rm3100-spi.c
> > @@ -0,0 +1,72 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Support for PNI RM3100 9-axis geomagnetic sensor a spi bus.
> > + *
> > + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> > + *
> > + * User Manual available at
> > + * <https://www.pnicorp.com/download/rm3100-user-manual/>
> 
> Probably only worth mentioning the manual in the main file.
> 
> > + */
> > +
> > +#include <linux/spi/spi.h>
> > +
> > +#include "rm3100.h"
> > +
> > +static const struct regmap_config rm3100_regmap_config = {
> > +		.reg_bits = 8,
> > +		.val_bits = 8,
> > +
> > +		.rd_table = &rm3100_readable_table,
> > +		.wr_table = &rm3100_writable_table,
> > +		.volatile_table = &rm3100_volatile_table,
> > +
> > +		.read_flag_mask = 0x80,
> > +
> > +		.cache_type = REGCACHE_RBTREE,
> > +};
> > +
> > +static int rm3100_probe(struct spi_device *spi)
> > +{
> > +	struct regmap *regmap;
> > +	int ret;
> > +
> > +	/* Actually this device supports both mode 0 and mode 3. */
> > +	spi->mode = SPI_MODE_0;
> > +	/* data rates cannot exceeds 1Mbits. */
> > +	spi->max_speed_hz = 1000000;
> > +	spi->bits_per_word = 8;
> > +	ret = spi_setup(spi);
> > +	if (ret)
> > +		return ret;
> > +
> > +	regmap =  devm_regmap_init_spi(spi, &rm3100_regmap_config);
> > +	if (IS_ERR(regmap))
> > +		return PTR_ERR(regmap);
> > +
> > +	return rm3100_common_probe(&spi->dev, regmap, spi->irq);
> > +}
> > +
> > +static int rm3100_remove(struct spi_device *spi)
> > +{
> > +	return rm3100_common_remove(&spi->dev);
> > +}
> > +
> > +static const struct of_device_id rm3100_dt_match[] = {
> > +	{ .compatible = "pni,rm3100-spi", },
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> > +
> > +static struct spi_driver rm3100_driver = {
> > +		.driver = {
> > +				.name = "rm3100-spi",
> > +				.of_match_table = rm3100_dt_match,
> 
> Indenting looks oddly deep...
> 
> > +		},
> > +		.probe = rm3100_probe,
> > +		.remove = rm3100_remove,
> > +};
> > +module_spi_driver(rm3100_driver);
> > +
> > +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> > +MODULE_DESCRIPTION("PNI RM3100 9-axis magnetometer spi driver");
> > +MODULE_LICENSE("GPL v2");
> > diff --git a/drivers/iio/magnetometer/rm3100.h b/drivers/iio/magnetometer/rm3100.h
> > new file mode 100644
> > index 000000000000..5e30bc0f5149
> > --- /dev/null
> > +++ b/drivers/iio/magnetometer/rm3100.h
> > @@ -0,0 +1,90 @@
> > +/* SPDX-License-Identifier: GPL-2.0+ */
> > +/*
> > + * Header file for PNI RM3100 driver
> > + *
> > + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> > + */
> > +
> > +#ifndef RM3100_CORE_H
> > +#define RM3100_CORE_H
> > +
> > +#include <linux/module.h>
> > +#include <linux/regmap.h>
> 
> What in here needs module.h?  Push that down into the
> individual c files.  It's repetition but it si generally
> good practice to include headers at as low a level as possible.
> 
> > +
> > +#define RM_REG_REV_ID		0x36
> I would prefer RM3100 as the prefix.
> > +
> > +/* Cycle Count Registers MSBs and LSBs. */
> Could probably give these slightly more human readable names?
> RM3100_REG_CC_X_MSB
> 
> Actually I doubt you use both of them in the driver anyway...
> (just searched, nope you don't so drop the ones you don't
>  use and then the MSB, LSB definition probably not necessary).
> 
> > +#define RM_REG_CCXM		0x04
> > +#define RM_REG_CCXL		0x05
> > +#define RM_REG_CCYM		0x06
> > +#define RM_REG_CCYL		0x07
> > +#define RM_REG_CCZM		0x08
> > +#define RM_REG_CCZL		0x09
> > +
> > +/* Single Measurement Mode register. */
> > +#define RM_REG_POLL		0x00
> > +#define RM_POLL_PMX		BIT(4)
> > +#define RM_POLL_PMY		BIT(5)
> > +#define RM_POLL_PMZ		BIT(6)
> > +
> > +/* Continues Measurement Mode register. */
> > +#define RM_REG_CMM		0x01
> > +#define RM_CMM_START		BIT(0)
> > +#define RM_CMM_DRDM		BIT(2)
> > +#define RM_CMM_PMX		BIT(4)
> > +#define RM_CMM_PMY		BIT(5)
> > +#define RM_CMM_PMZ		BIT(6)
> > +
> > +/* TiMe Rate Configuration register. */
> > +#define RM_REG_TMRC		0x0B
> > +#define RM_TMRC_OFFSET		0x92
> > +
> > +/* Result Status register. */
> > +#define RM_REG_STATUS		0x34
> > +#define RM_STATUS_DRDY		BIT(7)
> > +
> > +/* Measurement result registers. */
> > +#define RM_REG_MX2		0x24
> 
> You only use some of these. Not sure having defines for the
> others is really helpful.
> 
> > +#define RM_REG_MX1		0x25
> > +#define RM_REG_MX0		0x26
> > +#define RM_REG_MY2		0x27
> > +#define RM_REG_MY1		0x28
> > +#define RM_REG_MY0		0x29
> > +#define RM_REG_MZ2		0x2a
> > +#define RM_REG_MZ1		0x2b
> > +#define RM_REG_MZ0		0x2c
> > +
> > +#define RM_REG_HSHAKE		0x35
> > +
> > +#define RM_W_REG_START		RM_REG_POLL
> > +#define RM_W_REG_END		RM_REG_REV_ID
> > +#define RM_R_REG_START		RM_REG_POLL
> > +#define RM_R_REG_END		RM_REG_HSHAKE
> > +#define RM_V_REG_START		RM_REG_MX2
> > +#define RM_V_REG_END		RM_REG_HSHAKE
> > +
> > +/* Built-In Self Test reigister. */
> > +#define RM_REG_BIST		0x33
> > +
> > +struct rm3100_data {
> > +	struct device *dev;
> > +	struct regmap *regmap;
> > +	struct completion measuring_done;
> > +	bool use_interrupt;
> > +
> > +	int conversion_time;
> > +
> > +	/* To protect consistency of every measurement and sampling
> 
> /*
>  * To protect
>  */
> (common format to most of the kernel other than those 'crazy' :)
> people in net and a few other corners.
> 
> > +	 * frequency change operations.
> > +	 */
> > +	struct mutex lock;
> > +};
> > +
> > +extern const struct regmap_access_table rm3100_readable_table;
> > +extern const struct regmap_access_table rm3100_writable_table;
> > +extern const struct regmap_access_table rm3100_volatile_table;
> > +
> > +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq);
> > +int rm3100_common_remove(struct device *dev);
> > +
> > +#endif /* RM3100_CORE_H */
>