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Subject: Re: [PATCH 2/2] iio: accel: Add driver for Murata SCA3300
 accelerometer
From:   Tomas Melin <tomas.melin@vaisala.com>
To:     Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc:     jic23@kernel.org, devicetree@vger.kernel.org,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
        aardelean@deviqon.com
References: <20210412075056.56301-1-tomas.melin@vaisala.com>
 <20210412075056.56301-3-tomas.melin@vaisala.com>
 <20210412120807.000044d3@Huawei.com>
 <87302341-f9d0-372a-1f18-b934df202e82@vaisala.com>
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Date:   Fri, 16 Apr 2021 15:21:14 +0300
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Updated email-address for Alexandru.


On 4/16/21 3:17 PM, Tomas Melin wrote:
> On 4/15/21 11:41 AM, Tomas Melin wrote:
>
>>
>> While working on updates I did notice something new which I cannot
>>
>> reproduce on older (5.10.17 kernel) version. If compiling this as a 
>> module, getting error while
>>
>> unloading module:
>>
>> [   40.200084] Unable to handle kernel NULL pointer dereference at 
>> virtual address 00000104
>> ...
>>
>> [   40.510054] Backtrace:
>> [   40.512502] [<c06c5e0c>] (iio_device_ioctl_handler_unregister) 
>> from [<c06ca8c4>] (iio_buffers_free_sysfs_and_mask+0x2c/0x6c)
>> [   40.523735] [<c06ca898>] (iio_buffers_free_sysfs_and_mask) from 
>> [<c06c4a18>] (iio_device_unregister+0xa8/0xac)
>> [   40.533746]  r5:c1811228 r4:c1811000
>> [   40.537318] [<c06c4970>] (iio_device_unregister) from [<c06c4a38>] 
>> (devm_iio_device_unreg+0x1c/0x20)
>> [   40.546461]  r5:c2415000 r4:c25bab80
>> [   40.550025] [<c06c4a1c>] (devm_iio_device_unreg) from [<c0556820>] 
>> (release_nodes+0x1c0/0x1f0)
>> [   40.558654] [<c0556660>] (release_nodes) from [<c0556bb0>] 
>> (devres_release_all+0x40/0x60)
>> [   40.566847]  r10:00000081 r9:c2350000 r8:c0100264 r7:00000081 
>> r6:bf00c010 r5:c19be000
>> [   40.574669]  r4:c1a91c00
>> [   40.577194] [<c0556b70>] (devres_release_all) from [<c055216c>] 
>> (device_release_driver_internal+0x120/0x1cc)
>> [   40.587031]  r5:c19be000 r4:c1a91c00
>> [   40.590596] [<c055204c>] (device_release_driver_internal) from 
>> [<c05522b4>] (driver_detach+0x54/0x90)
>> [   40.599828]  r7:00000081 r6:00000000 r5:bf00c010 r4:c1a91c00
>> [   40.605482] [<c0552260>] (driver_detach) from [<c0550ba4>] 
>> (bus_remove_driver+0x5c/0xb0)
>> [   40.613583]  r5:00000800 r4:bf00c010
>> [   40.617148] [<c0550b48>] (bus_remove_driver) from [<c0552c38>] 
>> (driver_unregister+0x38/0x5c)
>> [   40.625596]  r5:00000800 r4:bf00c010
>> [   40.629161] [<c0552c00>] (driver_unregister) from [<bf00a760>] 
>> (sca3300_driver_exit+0x14/0x8b4 [sca3300])
>> [   40.638747]  r5:00000800 r4:bf00c080
>> [   40.642311] [<bf00a74c>] (sca3300_driver_exit [sca3300]) from 
>> [<c01c06f0>] (sys_delete_module+0x16c/0x238)
>> [   40.651990] [<c01c0584>] (sys_delete_module) from [<c0100244>] 
>> (__sys_trace_return+0x0/0x1c)
>> [   40.660435] Exception stack(0xc2351fa8 to 0xc2351ff0)
>> [   40.665484] 1fa0:                   0050e5a8 00000000 0050e5e4 
>> 00000800 081d4b00 bec18af4
>> [   40.673661] 1fc0: 0050e5a8 00000000 bec18b50 00000081 bec18e51 
>> 0050e190 00000001 bec18d3c
>> [   40.681834] 1fe0: 0050cf70 bec18afc 004f1ec8 b6ecb27c
>> [   40.686887]  r6:bec18b50 r5:00000000 r4:0050e5a8
>> [   40.691507] Code: e8bd4000 e1c020d0 e3a0cc01 e3001122 (e5823004)
>> [   40.707675] ---[ end trace 189882b050077333 ]---
>>
>> This happens when building against linux-next 
>> 5.12.0-rc6-next-20210409. I'm failing to see what is wrong. Any ideas?
>>
>> Thanks,
>>
>> Tomas
>
>
> Tested further that for this driver, loading and unloading as module 
> works fine until commit:
>
> commit f73f7f4da581875f9b1f2fb8ebd1ab15ed634488
> Author: Alexandru Ardelean <alexandru.ardelean@analog.com>
> Date:   Mon Feb 15 12:40:39 2021 +0200
>
>     iio: buffer: add ioctl() to support opening extra buffers for IIO 
> device
>
>
> Any thoughts what causes this issue?
>
> Thanks,
>
> Tomas
>
>
>
>>
>>
>>>
>>>> ---
>>>>   drivers/iio/accel/Kconfig   |  13 ++
>>>>   drivers/iio/accel/Makefile  |   1 +
>>>>   drivers/iio/accel/sca3300.c | 434 
>>>> ++++++++++++++++++++++++++++++++++++
>>>>   3 files changed, 448 insertions(+)
>>>>   create mode 100644 drivers/iio/accel/sca3300.c
>>>>
>>>> diff --git a/drivers/iio/accel/Kconfig b/drivers/iio/accel/Kconfig
>>>> index cceda3cecbcf..0dbf7b648e8a 100644
>>>> --- a/drivers/iio/accel/Kconfig
>>>> +++ b/drivers/iio/accel/Kconfig
>>>> @@ -450,6 +450,19 @@ config SCA3000
>>>>         To compile this driver as a module, say M here: the module 
>>>> will be
>>>>         called sca3000.
>>>>   +config SCA3300
>>>> +    tristate "Murata SCA3300 3-Axis Accelerometer Driver"
>>>> +    depends on SPI
>>>> +    select CRC8
>>>> +    select IIO_BUFFER
>>>> +    select IIO_TRIGGERED_BUFFER
>>>> +    help
>>>> +      Say yes here to build support for Murata SCA3300 3-Axis
>>>> +      accelerometer.
>>>> +
>>>> +      To compile this driver as a module, choose M here: the 
>>>> module will be
>>>> +      called sca3300.
>>>> +
>>>>   config STK8312
>>>>       tristate "Sensortek STK8312 3-Axis Accelerometer Driver"
>>>>       depends on I2C
>>>> diff --git a/drivers/iio/accel/Makefile b/drivers/iio/accel/Makefile
>>>> index 32cd1342a31a..4b56527a2b97 100644
>>>> --- a/drivers/iio/accel/Makefile
>>>> +++ b/drivers/iio/accel/Makefile
>>>> @@ -50,6 +50,7 @@ obj-$(CONFIG_MXC4005)        += mxc4005.o
>>>>   obj-$(CONFIG_MXC6255)        += mxc6255.o
>>>>     obj-$(CONFIG_SCA3000)        += sca3000.o
>>>> +obj-$(CONFIG_SCA3300)        += sca3300.o
>>>>     obj-$(CONFIG_STK8312)        += stk8312.o
>>>>   obj-$(CONFIG_STK8BA50)        += stk8ba50.o
>>>> diff --git a/drivers/iio/accel/sca3300.c b/drivers/iio/accel/sca3300.c
>>>> new file mode 100644
>>>> index 000000000000..112fb88ecd3a
>>>> --- /dev/null
>>>> +++ b/drivers/iio/accel/sca3300.c
>>>> @@ -0,0 +1,434 @@
>>>> +// SPDX-License-Identifier: GPL-2.0-only
>>>> +/*
>>>> + * Copyright (c) Vaisala Oyj. All rights reserved.
>>> Give a year for the copyright notice if you can.
>>>
>>>> + */
>>>> +#include <linux/crc8.h>
>>>> +#include <linux/delay.h>
>>>> +#include <linux/iio/buffer.h>
>>>> +#include <linux/iio/iio.h>
>>>> +#include <linux/iio/sysfs.h>
>>>> +#include <linux/iio/trigger_consumer.h>
>>>> +#include <linux/iio/triggered_buffer.h>
>>>> +#include <linux/kernel.h>
>>>> +#include <linux/module.h>
>>>> +#include <linux/spi/spi.h>
>>>> +
>>>> +#define SCA3300_ALIAS "sca3300"
>>>> +
>>>> +#define SCA3300_REG_STATUS 0x6
>>>> +#define SCA3300_REG_MODE 0xd
>>>> +#define SCA3300_REG_WHOAMI 0x10
>>>> +#define SCA3300_VALUE_SW_RESET 0x20
>>>> +#define SCA3300_CRC8_POLYNOMIAL 0x1d
>>>> +#define SCA3300_X_READ 0
>>> I wouldn't bother defining this.
>>>
>>>> +#define SCA3300_X_WRITE BIT(7)
>>> Even this one is something I'd just put inline with a comment.
>>>
>>>> +#define SCA3300_DEVICE_ID 0x51
>>>> +#define SCA3300_RS_ERROR 0x3
>>>> +
>>>> +enum sca3300_scan_indexes {
>>>> +    SCA3300_ACC_X = 0,
>>>> +    SCA3300_ACC_Y,
>>>> +    SCA3300_ACC_Z,
>>>> +    SCA3300_TEMP,
>>>> +    SCA3300_TIMESTAMP,
>>>> +};
>>>> +
>>>> +#define SCA3300_ACCEL_CHANNEL(index, reg, axis) { \
>>>> +        .type = IIO_ACCEL,                    \
>>>> +        .address = reg,                        \
>>>> +        .modified = 1,                        \
>>>> +        .channel2 = IIO_MOD_##axis,                \
>>>> +        .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
>>>> +                      BIT(IIO_CHAN_INFO_PROCESSED),    \
>>> As mentioned below, don't provide PROCESSED. Userspace is better at 
>>> handling the
>>> conversion so leave it to them.
>>>
>>>> +        .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),    \
>>>> +        .scan_index = index,                    \
>>>> +        .scan_type = {                        \
>>>> +            .sign = 's',                    \
>>>> +            .realbits = 16,                    \
>>>> +            .storagebits = 16,                \
>>>> +            .shift = 0,                    \
>>>> +            .endianness = IIO_CPU,                \
>>>> +        },                            \
>>>> +    }
>>>> +
>>>> +static const struct iio_chan_spec sca3300_channels[] = {
>>>> +    SCA3300_ACCEL_CHANNEL(SCA3300_ACC_X, 0x1, X),
>>>> +    SCA3300_ACCEL_CHANNEL(SCA3300_ACC_Y, 0x2, Y),
>>>> +    SCA3300_ACCEL_CHANNEL(SCA3300_ACC_Z, 0x3, Z),
>>>> +    {
>>>> +        .type = IIO_TEMP,
>>>> +        .address = 0x5,
>>>> +        .scan_index = SCA3300_TEMP,
>>>> +        .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
>>>> +        .scan_type = {
>>>> +            .sign = 's',
>>>> +            .realbits = 16,
>>>> +            .storagebits = 16,
>>>> +            .shift = 0,
>>>> +            .endianness = IIO_CPU,
>>>> +        },
>>>> +    },
>>>> +    IIO_CHAN_SOFT_TIMESTAMP(4),
>>>> +};
>>>> +
>>>> +static const int sca3300_accel_scale[] = {2700, 1350, 5400, 5400};
>>>> +
>>>> +static const unsigned long sca3300_scan_masks[] = {
>>>> +    BIT(SCA3300_ACC_X) | BIT(SCA3300_ACC_Y) | BIT(SCA3300_ACC_Z) |
>>>> +    BIT(SCA3300_TEMP),
>>>> +    0};
>>>> +
>>>> +/**
>>>> + * SCA3300 device data
>>> run scripts/kernel-doc over the file and fix the warnings + errors.
>>>
>>>> + *
>>>> + * @spi SPI device structure
>>>> + * @opmode Device operation mode
>>>> + * @lock Data buffer lock
>>>> + * @txbuf Transmit buffer
>>>> + * @rxbuf Receive buffer
>>>> + * @scan Triggered buffer. Four channel 16-bit data + 64-bit 
>>>> timestamp
>>>> + */
>>>> +struct sca3300_data {
>>>> +    struct spi_device *spi;
>>>> +    u32 opmode;
>>>> +    struct mutex lock;
>>>> +    u8 txbuf[4];
>>>> +    u8 rxbuf[4];
>>>> +    struct {
>>>> +        s16 channels[4];
>>>> +        s64 ts __aligned(sizeof(s64));
>>>> +    } scan;
>>>> +};
>>>> +
>>>> +DECLARE_CRC8_TABLE(sca3300_crc_table);
>>>> +
>>>> +static int sca3300_transfer(struct sca3300_data *sca_data, int *val)
>>>> +{
>>>> +    struct spi_delay delay = {.value = 10, .unit = 
>>>> SPI_DELAY_UNIT_USECS};
>>>> +    int32_t ret;
>>>> +    int rs;
>>>> +    u8 crc;
>>>> +    struct spi_transfer xfers[2] = {
>>>> +        {
>>>> +            .tx_buf = sca_data->txbuf,
>>>> +            .rx_buf = NULL,
>>>> +            .len = ARRAY_SIZE(sca_data->txbuf),
>>>> +            .delay = delay,
>>>> +            .cs_change = 1,
>>>> +        },
>>>> +        {
>>>> +            .tx_buf = NULL,
>>>> +            .rx_buf = sca_data->rxbuf,
>>>> +            .len = ARRAY_SIZE(sca_data->rxbuf),
>>>> +            .delay = delay,
>>>> +            .cs_change = 0,
>>>> +        }
>>>> +    };
>>>> +
>>>> +    /* inverted crc value as described in device data sheet */
>>>> +    crc = ~crc8(sca3300_crc_table, &sca_data->txbuf[0], 3, 
>>>> CRC8_INIT_VALUE);
>>>> +    sca_data->txbuf[3] = crc;
>>>> +
>>>> +    ret = spi_sync_transfer(sca_data->spi, xfers, 2);
>>> Use ARRAY_SIZE(xfers) instead of 2.
>>>
>>>> +    if (ret < 0) {
>>>> +        dev_err(&sca_data->spi->dev,
>>>> +            "transfer error, error: %d\n", ret);
>>>> +        return -EIO;
>>>> +    }
>>>> +
>>>> +    crc = ~crc8(sca3300_crc_table, &sca_data->rxbuf[0], 3, 
>>>> CRC8_INIT_VALUE);
>>>> +    if (sca_data->rxbuf[3] != crc) {
>>>> +        dev_err(&sca_data->spi->dev, "CRC checksum mismatch");
>>>> +        return -EIO;
>>>> +    }
>>>> +
>>>> +    /* get return status */
>>>> +    rs = sca_data->rxbuf[0] & 0x03;
>>>> +    if (rs == SCA3300_RS_ERROR)
>>>> +        return rs;
>>>> +
>>>> +    *val = (s16)(sca_data->rxbuf[2] | (sca_data->rxbuf[1] << 8));
>>> Preference for an unaligned endian conversion here and explicit sign 
>>> extend e.g
>>> something like
>>>
>>> sign_extend32(get_unaligned_le16(&sca_data->rxbuf[1]), 15)
>>>
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static int sca3300_read_reg(struct sca3300_data *sca_data, u8 reg, 
>>>> int *val)
>>>> +{
>>>> +    int ret;
>>>> +
>>>> +    mutex_lock(&sca_data->lock);
>>>> +    sca_data->txbuf[0] = SCA3300_X_READ | (reg << 2);
>>>> +    ret = sca3300_transfer(sca_data, val);
>>>> +    if (ret > 0) {
>>>> +        sca_data->txbuf[0] = SCA3300_X_READ | (SCA3300_REG_STATUS 
>>>> << 2);
>>>> +        ret = sca3300_transfer(sca_data, val);
>>>> +        /* status 0 = startup, 0x2 = mode change */
>>>> +        if (ret > 0 && *val != 0 && *val != 0x2) {
>>>> + dev_err_ratelimited(&sca_data->spi->dev,
>>>> +                        "device status: %x\n",
>>>> +                        (u16)*val);
>>>> +            mutex_unlock(&sca_data->lock);
>>>> +            return -EIO;
>>>> +        }
>>>> +        if (ret > 0)
>>>> +            ret = 0;
>>>> +    }
>>>> +    mutex_unlock(&sca_data->lock);
>>>> +
>>>> +    return ret;
>>>> +}
>>>> +
>>>> +static int sca3300_write_reg(struct sca3300_data *sca_data, u8 
>>>> reg, int val)
>>>> +{
>>>> +    int reg_val = 0;
>>>> +    int ret;
>>>> +
>>>> +    mutex_lock(&sca_data->lock);
>>>> +    sca_data->txbuf[0] = SCA3300_X_WRITE | (reg << 2);
>>>> +    sca_data->txbuf[1] = val >> 8;
>>>> +    sca_data->txbuf[2] = val & 0xFF;
>>> Prefer (Slightly) an unaligned put.
>>>
>>>> +    ret = sca3300_transfer(sca_data, &reg_val);
>>>> +    if (ret > 0) {
>>> Factor this error handling out to another function, plus trigger it 
>>> from an
>>> appropriate standard error code rather than a positive return value.
>>>
>>>> +        sca_data->txbuf[0] = SCA3300_X_READ | (SCA3300_REG_STATUS 
>>>> << 2);
>>>> +        ret = sca3300_transfer(sca_data, &reg_val);
>>>> +        /* status 0 = startup, 0x2 = mode change */
>>>> +        if (ret > 0 && reg_val != 0 && reg_val != 0x2) {
>>>> + dev_err_ratelimited(&sca_data->spi->dev,
>>>> +                        "device status: %x\n",
>>>> +                        (u16)reg_val);
>>>> +            mutex_unlock(&sca_data->lock);
>>>> +            return -EIO;
>>>> +        }
>>>> +        if (ret > 0)
>>>> +            ret = 0;
>>> Whenever you get this sort of juggling it rather implies your design is
>>> less than ideal.
>>>
>>>> +    }
>>>> +    mutex_unlock(&sca_data->lock);
>>>> +
>>>> +    return ret;
>>>> +}
>>>> +
>>>> +static int sca3300_write_raw(struct iio_dev *indio_dev,
>>>> +                 struct iio_chan_spec const *chan,
>>>> +                 int val, int val2, long mask)
>>>> +{
>>>> +    struct sca3300_data *data = iio_priv(indio_dev);
>>>> +
>>>> +    switch (mask) {
>>>> +    case IIO_CHAN_INFO_SCALE:
>>>> +        if (val < 0 || val > 3)
>>>> +            return -EINVAL;
>>> No.  Scale values need to be the value of 1LSB not a random integer
>>> that requires you to look up the datasheet.
>>>
>>>> +        return sca3300_write_reg(data, SCA3300_REG_MODE, val);
>>>> +    default:
>>>> +        return -EINVAL;
>>>> +    }
>>>> +}
>>>> +
>>>> +static int sca3300_read_raw(struct iio_dev *indio_dev,
>>>> +                struct iio_chan_spec const *chan,
>>>> +                int *val, int *val2, long mask)
>>>> +{
>>>> +    struct sca3300_data *data = iio_priv(indio_dev);
>>>> +    int ret;
>>>> +    int reg_val;
>>>> +
>>>> +    switch (mask) {
>>>> +    case IIO_CHAN_INFO_RAW:
>>>> +        ret = sca3300_read_reg(data, chan->address, val);
>>>> +        if (ret < 0)
>>>> +            return ret;
>>>> +        return IIO_VAL_INT;
>>>> +    case IIO_CHAN_INFO_SCALE:
>>>> +        ret = sca3300_read_reg(data, SCA3300_REG_MODE, &reg_val);
>>>> +        if (ret < 0)
>>>> +            return ret;
>>>> +        *val = sca3300_accel_scale[reg_val];
>>> Scale is very very rarely an integer value which makes me wonder what
>>> you are returning here...  It should be the multiplier needed to
>>> take the raw value to a reading in m/sec^2  Given you use it as 
>>> fractional
>>> below, I'm guessing this is 1/scale_value?
>>>
>>>> +        return IIO_VAL_INT;
>>>> +    case IIO_CHAN_INFO_PROCESSED:
>>> Don't provide processed here.   Userspace needs to do the conversion 
>>> itself
>>> (and given it has floating point easily available will probably do a 
>>> better
>>>   job than we can).   I'm assuming the mode can't autonomously change?
>>>
>>>> +        ret = sca3300_read_reg(data, SCA3300_REG_MODE, &reg_val);
>>>> +        if (ret < 0)
>>>> +            return ret;
>>>> +        *val2 = sca3300_accel_scale[reg_val];
>>>> +        ret = sca3300_read_reg(data, chan->address, val);
>>>> +        if (ret < 0)
>>>> +            return ret;
>>>> +        return IIO_VAL_FRACTIONAL;
>>>> +    default:
>>>> +        return -EINVAL;
>>>> +    }
>>>> +}
>>>> +
>>>> +static irqreturn_t sca3300_trigger_handler(int irq, void *p)
>>>> +{
>>>> +    struct iio_poll_func *pf = p;
>>>> +    struct iio_dev *indio_dev = pf->indio_dev;
>>>> +    struct sca3300_data *data = iio_priv(indio_dev);
>>>> +    s64 time_ns = iio_get_time_ns(indio_dev);
>>> Is the timestamp at the start more accurate that that at the end
>>> of reading the channels?  If not, just put this inline in the
>>> iio_push_to_buffers_with_timestamp() call.
>>>
>>>> +    int bit, ret, val, i = 0;
>>>> +
>>>> +    for_each_set_bit(bit, indio_dev->active_scan_mask,
>>>> +             indio_dev->masklength) {
>>>> +        ret = sca3300_read_reg(data, sca3300_channels[bit].address,
>>>> +                       &val);
>>>> +        if (ret < 0)
>>> Given we can't return an error code from interrupt handlers, it is 
>>> usually
>>> a good idea to print something to the log. Otherwise we get missing 
>>> data
>>> with no idea of why..
>>>
>>>> +            goto out;
>>>> +        if (ARRAY_SIZE(data->scan.channels) > i)
>>> How could this not be true?  If it's always true, don't bother
>>> checking i.
>>>
>>>> +            ((s16 *)data->scan.channels)[i++] = val;
>>>> +    }
>>>> +
>>>> +    iio_push_to_buffers_with_timestamp(indio_dev, &data->scan, 
>>>> time_ns);
>>>> +out:
>>>> +    iio_trigger_notify_done(indio_dev->trig);
>>>> +
>>>> +    return IRQ_HANDLED;
>>>> +}
>>>> +
>>>> +static int sca3300_init(struct sca3300_data *sca_data,
>>>> +            struct iio_dev *indio_dev)
>>>> +{
>>>> +    int ret;
>>>> +    int value = 0;
>>>> +
>>>> +    if (sca_data->opmode < 1 || sca_data->opmode > 4)
>>>> +        return -EINVAL;
>>> Whilst this is going anyway, better to check that next to where
>>> it is read so we drop out immediately rather than buried in this
>>> function.
>>>
>>>> +
>>>> +    ret = sca3300_write_reg(sca_data, SCA3300_REG_MODE,
>>>> +                SCA3300_VALUE_SW_RESET);
>>>> +    if (ret != 0)
>>>> +        return ret;
>>> For sleeps, good to reference which section in data sheet gives the
>>> timing.
>>>
>>>> +    usleep_range(2e3, 10e3);
>>>> +
>>>> +    ret = sca3300_write_reg(sca_data, SCA3300_REG_MODE,
>>>> +                sca_data->opmode - 1);
>>>> +    if (ret != 0)
>>> if (ret) see below.
>>>
>>>> +        return ret;
>>>> +    msleep(100);
>>> Again, document where the time comes from. Saves reviewers time if
>>> they want to check it. (I'm too lazy :)
>>>
>>>> +    ret = sca3300_read_reg(sca_data, SCA3300_REG_WHOAMI, &value);
>>>> +    if (ret != 0)
>>> if (ret) is more idiomatic in kernel code.
>>>
>>>> +        return ret;
>>>> +
>>>> +    if (value != SCA3300_DEVICE_ID) {
>>>> +        dev_err(&sca_data->spi->dev, "device id not expected 
>>>> value\n");
>>> Perhaps useful to print what was expected and what was seen. Maybe it's
>>> a new variant and this might help the user to identify that and add 
>>> it to the
>>> driver.
>>>
>>>> +        return -EIO;
>>> -EINVAL probably more appropriate return.
>>>
>>>> +    }
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static int sca3300_debugfs_reg_access(struct iio_dev *indio_dev,
>>>> +                      unsigned int reg, unsigned int writeval,
>>>> +                      unsigned int *readval)
>>>> +{
>>>> +    struct sca3300_data *data = iio_priv(indio_dev);
>>>> +    int value;
>>>> +    int ret;
>>>> +
>>>> +    if (reg > 0x1f)
>>> Use a define that names that register.
>>>
>>>> +        return -EINVAL;
>>>> +
>>>> +    if (!readval)
>>>> +        return sca3300_write_reg(data, reg, writeval);
>>>> +
>>>> +    ret = sca3300_read_reg(data, reg, &value);
>>>> +    if (ret < 0)
>>>> +        return ret;
>>>> +
>>>> +    *readval = (unsigned int)value;
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static const struct iio_info sca3300_info = {
>>>> +    .read_raw = sca3300_read_raw,
>>>> +    .write_raw = sca3300_write_raw,
>>>> +    .debugfs_reg_access = &sca3300_debugfs_reg_access,
>>>> +};
>>>> +
>>>> +static int sca3300_probe(struct spi_device *spi)
>>>> +{
>>>> +    struct sca3300_data *sca_data;
>>>> +    struct iio_dev *indio_dev;
>>>> +    int ret;
>>>> +
>>>> +    indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*sca_data));
>>>> +    if (!indio_dev) {
>>>> +        dev_err(&spi->dev,
>>>> +            "failed to allocate memory for iio device\n");
>>>> +        return -ENOMEM;
>>>> +    }
>>>> +
>>>> +    sca_data = iio_priv(indio_dev);
>>>> +    mutex_init(&sca_data->lock);
>>>> +    sca_data->spi = spi;
>>>> +    spi_set_drvdata(spi, indio_dev);
>>> Won't be used once using devm as below and remove() is dropped, so 
>>> drop this.
>>>
>>>> +
>>>> +    crc8_populate_msb(sca3300_crc_table, SCA3300_CRC8_POLYNOMIAL);
>>>> +
>>>> +    indio_dev->dev.parent = &spi->dev;
>>>> +    indio_dev->info = &sca3300_info;
>>>> +    indio_dev->name = SCA3300_ALIAS;
>>>> +    indio_dev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_TRIGGERED;
>>> BUFFER_TRIGGERED bit now set by iio_triggered_buffer_setup() so 
>>> shouldn't
>>> be ehre as well.
>>>
>>>> +    indio_dev->channels = sca3300_channels;
>>>> +    indio_dev->num_channels = ARRAY_SIZE(sca3300_channels);
>>>> +    indio_dev->available_scan_masks = sca3300_scan_masks;
>>>> +
>>>> +    if (spi->dev.of_node) {
>>>> +        ret = of_property_read_u32(spi->dev.of_node, "murata,opmode",
>>> Please use generic firmware access calls rather than the of specific 
>>> ones.
>>> That lets us get ACPI support for free :)
>>>
>>> As per the binding review however, this one needs to go in favour of 
>>> userspace
>>> control of scale + filter frequencies / sampling freq.
>>>
>>>> + &sca_data->opmode);
>>>> +        if (ret < 0)
>>>> +            return ret;
>>>> +    }
>>>> +
>>>> +    ret = sca3300_init(sca_data, indio_dev);
>>>> +    if (ret < 0) {
>>>> +        dev_err(&spi->dev, "failed to init device, error: %d\n", 
>>>> ret);
>>>> +        return ret;
>>>> +    }
>>>> +
>>>> +    ret = iio_triggered_buffer_setup(indio_dev, 
>>>> iio_pollfunc_store_time,
>>>> +                     sca3300_trigger_handler, NULL);
>>> devm_iio_triggered_buffer_setup() and you can drop the manual 
>>> cleanup in remove()
>>> and hence drop remove() entirely as nothing else left.
>>>
>>>> +    if (ret < 0) {
>>>> +        dev_err(&spi->dev,
>>>> +            "iio triggered buffer setup failed, error: %d\n", ret);
>>>> +        return ret;
>>>> +    }
>>>> +
>>>> +    ret = devm_iio_device_register(&spi->dev, indio_dev);
>>>> +    if (ret < 0) {
>>>> +        dev_err(&spi->dev, "iio device register failed, error: %d\n",
>>>> +            ret);
>>>> +        iio_triggered_buffer_cleanup(indio_dev);
>>> With devm above, no need to manually clean this up.
>>>
>>>> +        return ret;
>>>> +    }
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static int sca3300_remove(struct spi_device *spi)
>>>> +{
>>>> +    struct iio_dev *indio_dev = spi_get_drvdata(spi);
>>>> +
>>>> +    iio_triggered_buffer_cleanup(indio_dev);
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static const struct of_device_id sca3300_dt_ids[] = {
>>>> +    { .compatible = "murata,sca3300"},
>>>> +    {},
>>>> +};
>>>> +MODULE_DEVICE_TABLE(of, sca3300_dt_ids);
>>>> +
>>>> +static struct spi_driver sca3300_driver = {
>>>> +    .driver = {
>>>> +        .name        = SCA3300_ALIAS,
>>>> +        .owner        = THIS_MODULE,
>>>> +        .of_match_table = of_match_ptr(sca3300_dt_ids),
>>>> +    },
>>>> +
>>>> +    .probe    = sca3300_probe,
>>>> +    .remove    = sca3300_remove,
>>>> +};
>>>> +
>>>> +module_spi_driver(sca3300_driver);
>>>> +
>>>> +MODULE_AUTHOR("Tomas Melin <tomas.melin@vaisala.com>");
>>>> +MODULE_DESCRIPTION("Murata SCA3300 SPI Accelerometer");
>>>> +MODULE_LICENSE("GPL v2");