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Date: Sun, 20 Sep 2015 22:35:37 -0700
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: peda@...ator.liu.se
Cc: linux-kernel@...r.kernel.org, Peter Rosin <peda@...ntia.se>,
Jonathan Corbet <corbet@....net>,
Arnd Bergmann <arnd@...db.de>, linux-doc@...r.kernel.org
Subject: Re: [PATCH] misc: mcp4xxx_dpot: Driver for Microchip digital
potentiometers
On Mon, Aug 31, 2015 at 10:08:08PM +0200, peda@...ator.liu.se wrote:
> From: Peter Rosin <peda@...ntia.se>
>
> Signed-off-by: Peter Rosin <peda@...ntia.se>
A whole new driver with exactly no changelog description at all? I
can't take that :(
> ---
> Documentation/misc-devices/mcp4xxx_dpot.txt | 47 +++++
> MAINTAINERS | 5 +
> drivers/misc/Kconfig | 15 ++
> drivers/misc/Makefile | 1 +
> drivers/misc/mcp4xxx_dpot.c | 269 +++++++++++++++++++++++++++
> drivers/misc/mcp4xxx_dpot.h | 44 +++++
> 6 files changed, 381 insertions(+)
> create mode 100644 Documentation/misc-devices/mcp4xxx_dpot.txt
> create mode 100644 drivers/misc/mcp4xxx_dpot.c
> create mode 100644 drivers/misc/mcp4xxx_dpot.h
>
> This patch has two checkpatch errors but I really don't know how to fix them.
> The offending code was copied from drivers/misc/ad525x_dpot.c and the errors
> are:
>
> ERROR: Macros with complex values should be enclosed in parentheses
> #266: FILE: drivers/misc/mcp4xxx_dpot.c:129:
> +#define MCP4XXX_DPOT_DEVICE_SHOW_SET(name, reg) \
> +MCP4XXX_DPOT_DEVICE_SHOW(name, reg) \
> +MCP4XXX_DPOT_DEVICE_SET(name, reg) \
> +static DEVICE_ATTR(name, S_IWUSR | S_IRUGO, show_##name, set_##name)
>
> ERROR: Macros with complex values should be enclosed in parentheses
> #271: FILE: drivers/misc/mcp4xxx_dpot.c:134:
> +#define MCP4XXX_DPOT_DEVICE_SHOW_ONLY(name, reg) \
> +MCP4XXX_DPOT_DEVICE_SHOW(name, reg) \
> +static DEVICE_ATTR(name, S_IWUSR | S_IRUGO, show_##name, NULL)
>
> I have tried to add various parentheses, but no luck.
>
> I am also unsure if I have modelled this on deprecated stuff. Is
> there a better place to add a digital potentiometer driver?
>
> Industrial IO perhaps? In any case, this is a sufficient implementation
> for my needs, and a more complex user-space api is only going to be a
> burden.
>
> Cheers,
> Peter
>
> diff --git a/Documentation/misc-devices/mcp4xxx_dpot.txt b/Documentation/misc-devices/mcp4xxx_dpot.txt
> new file mode 100644
> index 000000000000..10ed02958775
> --- /dev/null
> +++ b/Documentation/misc-devices/mcp4xxx_dpot.txt
> @@ -0,0 +1,47 @@
> +---------------------------------
> + MCP4XXX Digital Potentiometers
> +---------------------------------
> +
> +The mcp4xxx_dpot driver exports a simple sysfs interface. This allows you to
> +work with the immediate resistance settings.
sysfs files all need to be documented in Documentation/ABI/ not in
random Documentation files :)
Also, why isn't this just an IIO driver? Creating one-off sysfs files
for each driver is a path to madness, please work on using standard
interfaces if at all possible.
> +---------
> + Files
> +---------
> +
> +Each dpot device will have its own rdac files. How many depends on the actual
> +part you have, as will the range of allowed values.
> +
> +This rdac file is used to program the immediate value of the device.
> +
> +-----------
> + Example
> +-----------
> +
> +Locate the device in your sysfs tree. This is probably easiest by going into
> +the common i2c directory and locating the device by the i2c slave address.
> +
> + # ls /sys/bus/i2c/devices/
> + 0-0028 0-0050
> +
> +So assuming the device in question is on the first i2c bus and has the slave
> +address of 0x28, we descend (unrelated sysfs entries have been trimmed).
> +
> + # ls /sys/bus/i2c/devices/0-0028/
> + rdac0 rdac1
> +
> +You can use simple reads/writes to access these files:
> +
> + # cd /sys/bus/i2c/devices/0-0028/
> +
> + # cat rdac0
> + 0
> + # echo 128 > rdac0
> + # cat rdac0
> + 128
> +
> + # cat rdac1
> + 5
> + # echo 35 > rdac1
> + # cat rdac1
> + 35
You never say what the contents of these files really are. Nor what the
units are, if any, or what this driver even does or is used for. For
all I know it just is a sysfs file value storage driver :)
> diff --git a/MAINTAINERS b/MAINTAINERS
> index b60e2b2369d2..c7bc2cc8051d 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6600,6 +6600,11 @@ W: http://linuxtv.org
> S: Maintained
> F: drivers/media/radio/radio-maxiradio*
>
> +MPC4XXX MICROCHIP DIGITAL POTENTIOMETERS DRIVER
> +M: Peter Rosin <peda@...ntia.se>
> +S: Maintained
> +F: drivers/misc/mcp4xxx_dpot.*
> +
> MEDIA DRIVERS FOR RENESAS - VSP1
> M: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> L: linux-media@...r.kernel.org
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 42c38525904b..a4e5e42b6b92 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -51,6 +51,21 @@ config AD525X_DPOT_SPI
> To compile this driver as a module, choose M here: the
> module will be called ad525x_dpot-spi.
>
> +config MCP4XXX_DPOT
> + tristate "Microchip Digital Potentiometer"
> + depends on I2C && SYSFS
> + help
> + If you say yes here, you get support for the Microchip
> + MCP4531, MCP4532, MCP4551, MCP4552,
> + MCP4631, MCP4632, MCP4651, MCP4652,
> + digital potentiometer chips.
> +
> + See Documentation/misc-devices/mcp4xxx_dpot.txt for the
> + userspace interface.
> +
> + This driver can also be built as a module. If so, the module
> + will be called mcp4xxx_dpot.
> +
> config ATMEL_TCLIB
> bool "Atmel AT32/AT91 Timer/Counter Library"
> depends on (AVR32 || ARCH_AT91)
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index d056fb7186fe..bb8c2994fd98 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -15,6 +15,7 @@ obj-$(CONFIG_BMP085_SPI) += bmp085-spi.o
> obj-$(CONFIG_DUMMY_IRQ) += dummy-irq.o
> obj-$(CONFIG_ICS932S401) += ics932s401.o
> obj-$(CONFIG_LKDTM) += lkdtm.o
> +obj-$(CONFIG_MCP4XXX_DPOT) += mcp4xxx_dpot.o
> obj-$(CONFIG_TIFM_CORE) += tifm_core.o
> obj-$(CONFIG_TIFM_7XX1) += tifm_7xx1.o
> obj-$(CONFIG_PHANTOM) += phantom.o
> diff --git a/drivers/misc/mcp4xxx_dpot.c b/drivers/misc/mcp4xxx_dpot.c
> new file mode 100644
> index 000000000000..abacae99ae42
> --- /dev/null
> +++ b/drivers/misc/mcp4xxx_dpot.c
> @@ -0,0 +1,269 @@
> +/*
> + * mcp4xxx_dpot: Driver for Microchip digital potentiometers
> + * Copyright (c) 2015 Axentia Technologies AB
> + * Author: Peter Rosin <peda@...ntia.se>
> + *
> + * DEVID #Wipers #Positions Resistor Options (kOhm)
> + * mcp4531 1 129 5, 10, 50, 100
> + * mcp4532 1 129 5, 10, 50, 100
> + * mcp4551 1 257 5, 10, 50, 100
> + * mcp4552 1 257 5, 10, 50, 100
> + * mcp4631 2 129 5, 10, 50, 100
> + * mcp4632 2 129 5, 10, 50, 100
> + * mcp4651 2 257 5, 10, 50, 100
> + * mcp4652 2 257 5, 10, 50, 100
> + *
> + * See Documentation/misc-devices/mcp4xxx_dpot.txt for more info.
> + *
> + * derived from ad525x.c
> + * Copyright (c) 2009-2010 Analog Devices, Inc.
> + * Author: Michael Hennerich <hennerich@...ckfin.uclinux.org>
> + *
> + * derived from ad5258.c
> + * Copyright (c) 2009 Cyber Switching, Inc.
> + * Author: Chris Verges <chrisv@...erswitching.com>
> + *
> + * derived from ad5252.c
> + * Copyright (c) 2006-2011 Michael Hennerich <hennerich@...ckfin.uclinux.org>
> + *
> + * Licensed under the GPL-2 or later.
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +
> +#include "mcp4xxx_dpot.h"
> +
> +/*
> + * Client data (each client gets its own)
> + */
> +
> +struct mcp4xxx_dpot_data {
> + struct i2c_client *client;
> + struct mutex update_lock;
> + unsigned max_pos;
> + unsigned long devid;
> + unsigned uid;
> + unsigned wipers;
> +};
> +
> +static s32 mcp4xxx_dpot_read(struct mcp4xxx_dpot_data *dpot, u8 reg)
> +{
> + s32 value;
> +
> + value = i2c_smbus_read_word_data(dpot->client, (reg << 4) | 0xc);
> + if (value < 0)
> + return value;
> + return ((value >> 8) & 0xff) | ((value & 0xff) << 8);
> +}
> +
> +static s32 mcp4xxx_dpot_write(struct mcp4xxx_dpot_data *dpot,
> + u8 reg, u16 value)
> +{
> + return i2c_smbus_write_byte_data(dpot->client,
> + (reg << 4) | value >> 8,
> + value & 0xff);
> +}
> +
> +/* sysfs functions */
> +
> +static ssize_t mcp4xxx_sysfs_show_reg(struct device *dev,
> + struct device_attribute *attr,
> + char *buf, u32 reg)
> +{
> + struct mcp4xxx_dpot_data *data = dev_get_drvdata(dev);
> + s32 value;
> +
> + mutex_lock(&data->update_lock);
> + value = mcp4xxx_dpot_read(data, reg);
> + mutex_unlock(&data->update_lock);
> +
> + if (value < 0)
> + return -EINVAL;
> +
> + return sprintf(buf, "%u\n", value);
> +}
> +
> +static ssize_t mcp4xxx_sysfs_set_reg(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count, u32 reg)
> +{
> + struct mcp4xxx_dpot_data *data = dev_get_drvdata(dev);
> + unsigned long value;
> + int err;
> +
> + err = kstrtoul(buf, 10, &value);
> + if (err)
> + return err;
> +
> + if (value >= data->max_pos)
> + value = data->max_pos - 1;
> +
> + mutex_lock(&data->update_lock);
> + mcp4xxx_dpot_write(data, reg, value);
> + mutex_unlock(&data->update_lock);
> +
> + return count;
> +}
> +
> +/* ------------------------------------------------------------------------- */
> +
> +#define MCP4XXX_DPOT_DEVICE_SHOW(_name, _reg) \
> +static ssize_t show_##_name(struct device *dev, \
> + struct device_attribute *attr, char *buf) \
> +{ \
> + return mcp4xxx_sysfs_show_reg(dev, attr, buf, _reg); \
> +}
> +
> +#define MCP4XXX_DPOT_DEVICE_SET(_name, _reg) \
> +static ssize_t set_##_name(struct device *dev, \
> + struct device_attribute *attr, \
> + const char *buf, size_t count) \
> +{ \
> + return mcp4xxx_sysfs_set_reg(dev, attr, buf, count, _reg); \
> +}
> +
> +#define MCP4XXX_DPOT_DEVICE_SHOW_SET(name, reg) \
> +MCP4XXX_DPOT_DEVICE_SHOW(name, reg) \
> +MCP4XXX_DPOT_DEVICE_SET(name, reg) \
> +static DEVICE_ATTR(name, S_IWUSR | S_IRUGO, show_##name, set_##name)
DEVICE_ATTR_RW()?
> +
> +#define MCP4XXX_DPOT_DEVICE_SHOW_ONLY(name, reg) \
> +MCP4XXX_DPOT_DEVICE_SHOW(name, reg) \
> +static DEVICE_ATTR(name, S_IWUSR | S_IRUGO, show_##name, NULL)
DEVICE_ATTR_RW()?
> +
> +MCP4XXX_DPOT_DEVICE_SHOW_SET(rdac0, DPOT_ADDR_RDAC | DPOT_RDAC0);
> +MCP4XXX_DPOT_DEVICE_SHOW_SET(rdac1, DPOT_ADDR_RDAC | DPOT_RDAC1);
That's a bunch of macros for just 2 files, you could just spell them out
which would make things easier...
> +
> +static const struct attribute *mcp4xxx_dpot_attrib_wipers[] = {
> + &dev_attr_rdac0.attr,
> + &dev_attr_rdac1.attr,
> + NULL
> +};
> +
> +/* ------------------------------------------------------------------------- */
> +
> +static int mcp4xxx_dpot_add_files(struct device *dev, unsigned rdac)
> +{
> + int err = sysfs_create_file(&dev->kobj,
> + mcp4xxx_dpot_attrib_wipers[rdac]);
> +
Oops, you just raced with userspace and it never saw your sysfs file
created :(
You need to use an attribute group instead.
Or better yet, the IIO interface please.
> + if (err)
> + dev_err(dev, "failed to register sysfs hooks for RDAC%d\n",
> + rdac);
> +
> + return err;
> +}
> +
> +static inline void mcp4xxx_dpot_remove_files(struct device *dev, unsigned rdac)
> +{
> + sysfs_remove_file(&dev->kobj,
> + mcp4xxx_dpot_attrib_wipers[rdac]);
> +}
> +
> +static int mcp4xxx_dpot_i2c_probe(struct i2c_client *client,
> + const struct i2c_device_id *id)
> +{
> + struct device *dev = &client->dev;
> + unsigned long devid = id->driver_data;
> + const char *name = id->name;
> + struct mcp4xxx_dpot_data *data;
> + int i, err = 0;
> +
> + if (!i2c_check_functionality(client->adapter,
> + I2C_FUNC_SMBUS_WORD_DATA)) {
> + dev_err(&client->dev, "SMBUS Word Data not Supported\n");
> + return -EIO;
> + }
> +
> + data = kzalloc(sizeof(struct mcp4xxx_dpot_data), GFP_KERNEL);
> + if (!data) {
> + err = -ENOMEM;
> + goto exit;
> + }
> +
> + dev_set_drvdata(dev, data);
> + mutex_init(&data->update_lock);
> +
> + data->client = client;
> + data->devid = devid;
> +
> + data->max_pos = (1 << DPOT_MAX_POS(devid)) + 1;
> + data->uid = DPOT_UID(devid);
> + data->wipers = DPOT_WIPERS(devid);
> +
> + for (i = DPOT_RDAC0; i < MAX_RDACS; i++) {
> + if (!(data->wipers & (1 << i)))
> + continue;
> + if (mcp4xxx_dpot_add_files(dev, i))
> + goto exit_remove_files;
> + }
> +
> + dev_info(dev, "%s %d-Position Digital Potentiometer registered\n",
> + name, data->max_pos);
Don't be "noisy", if a driver is working properly, nothing should show
up in the kernel log. Otherwise it's a total mess.
thanks,
greg k-h
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