Re: [PATCH v3 5/7] iio: accel: kionix-kx022a: Refactor driver and add chip_info structure

Matti Vaittinen
2023-04-25T08:12:18Z

On 4/25/23 10:24, Mehdi Djait wrote:
> Hi Matti,
>
> On Tue, Apr 25, 2023 at 09:50:11AM +0300, Matti Vaittinen wrote:
>> On 4/25/23 01:22, Mehdi Djait wrote:
>>> Add the chip_info structure to the driver's private data to hold all
>>> the device specific infos.
>>> Refactor the kx022a driver implementation to make it more generic and
>>> extensible.
>>>
>>> Signed-off-by: Mehdi Djait <mehdi.djait.k@gmail.com>
>>> ---
>>> v3:
>>> - added the change of the buffer's allocation in the __kx022a_fifo_flush
>>> to this patch
>>> - added the chip_info to the struct kx022a_data
>>>
>>> v2:
>>> - mentioned the introduction of the i2c_device_id table in the commit
>>> - get i2c_/spi_get_device_id only when device get match fails
>>> - removed the generic KX_define
>>> - removed the kx022a_device_type enum
>>> - added comments for the chip_info struct elements
>>> - fixed errors pointed out by the kernel test robot
>>>
>>> drivers/iio/accel/kionix-kx022a-i2c.c | 15 +++-
>>> drivers/iio/accel/kionix-kx022a-spi.c | 15 +++-
>>> drivers/iio/accel/kionix-kx022a.c | 114 +++++++++++++++++---------
>>> drivers/iio/accel/kionix-kx022a.h | 54 +++++++++++-
>>> 4 files changed, 147 insertions(+), 51 deletions(-)
>>>
>>> diff --git a/drivers/iio/accel/kionix-kx022a-i2c.c b/drivers/iio/accel/kionix-kx022a-i2c.c
>>> index 8f23631a1fd3..ce299d0446f7 100644
>>> --- a/drivers/iio/accel/kionix-kx022a-i2c.c
>>> +++ b/drivers/iio/accel/kionix-kx022a-i2c.c
>>> @@ -15,6 +15,7 @@
>>
>> ...
>>
>>
>>> static int __kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples,
>>> @@ -600,13 +600,17 @@ static int __kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples,
>>> {
>>> struct kx022a_data *data = iio_priv(idev);
>>> struct device *dev = regmap_get_device(data->regmap);
>>> - __le16 buffer[KX022A_FIFO_LENGTH * 3];
>>> + __le16 *buffer;
>>> uint64_t sample_period;
>>> int count, fifo_bytes;
>>> bool renable = false;
>>> int64_t tstamp;
>>> int ret, i;
>>> + buffer = kmalloc(data->chip_info->fifo_length * KX022A_FIFO_SAMPLES_SIZE_BYTES, GFP_KERNEL);
>>> + if (!buffer)
>>> + return -ENOMEM;
>>
>> Do you think we could get rid of allocating and freeing the buffer for each
>> flush? I feel it is a bit wasteful, and with high sampling frequencies this
>> function can be called quite often. Do you think there would be a way to
>> either use stack (always reserve big enough buffer no matter which chip we
>> have - or is the buffer too big to be safely taken from the stack?), or a
>> buffer stored in private data and allocated at probe or buffer enable?
>
> I tried using the same allocation as before but a device like the KX127
> has a fifo_length of 342 (compared to 86 for kx132, and 43 for kx022a).
> Allocating this much using the stack will result in a Warning.
>

Right. Maybe you could then have the buffer in private-data and allocate
it in buffer pre-enable? Do you think that would work?

>>
>> Also, please avoid such long lines. I know many people don't care about the
>> line length - but for example I tend to have 3 terminal windows open
>> side-by-side on my laptop screen. Hence long lines tend to be harder to read
>> for me.
>
> That is the case for me also, but Jonathan asked me to change
> "fifo_length * 6" and the KX022A_FIFO_SAMPLES_SIZE_BYTES is already
> defined.

then please maybe split the line from appropriate point like:
buffer = kmalloc(data->chip_info->fifo_length *
KX022A_FIFO_SAMPLES_SIZE_BYTES, GFP_KERNEL);

>
>>
>>> +
>>> ret = regmap_read(data->regmap, KX022A_REG_BUF_STATUS_1, &fifo_bytes);
>>> if (ret) {
>>> dev_err(dev, "Error reading buffer status\n");
>>> @@ -621,8 +625,10 @@ static int __kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples,
>>> dev_warn(data->dev, "Bad FIFO alignment. Data may be corrupt\n");
>>> count = fifo_bytes / KX022A_FIFO_SAMPLES_SIZE_BYTES;
>>> - if (!count)
>>> + if (!count) {
>>> + kfree(buffer);
>>> return 0;
>>> + }
>>> /*
>>> * If we are being called from IRQ handler we know the stored timestamp
>>> @@ -679,7 +685,7 @@ static int __kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples,
>>> }
>>> fifo_bytes = count * KX022A_FIFO_SAMPLES_SIZE_BYTES;
>>> - ret = regmap_noinc_read(data->regmap, KX022A_REG_BUF_READ,
>>> + ret = regmap_noinc_read(data->regmap, data->chip_info->buf_read,
>>> &buffer[0], fifo_bytes);
>>> if (ret)
>>> goto renable_out;
>>> @@ -704,6 +710,7 @@ static int __kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples,
>>> if (renable)
>>> enable_irq(data->irq);
>>> + kfree(buffer);
>>> return ret;
>>> }
>>>
>> ...
>>
>>> -int kx022a_probe_internal(struct device *dev)
>>> +const struct kx022a_chip_info kx022a_chip_info = {
>>> + .name = "kx022-accel",
>>> + .regmap_config = &kx022a_regmap_config,
>>> + .channels = kx022a_channels,
>>> + .num_channels = ARRAY_SIZE(kx022a_channels),
>>> + .fifo_length = KX022A_FIFO_LENGTH,
>>> + .who = KX022A_REG_WHO,
>>> + .id = KX022A_ID,
>>> + .cntl = KX022A_REG_CNTL,
>>> + .cntl2 = KX022A_REG_CNTL2,
>>> + .odcntl = KX022A_REG_ODCNTL,
>>> + .buf_cntl1 = KX022A_REG_BUF_CNTL1,
>>> + .buf_cntl2 = KX022A_REG_BUF_CNTL2,
>>> + .buf_clear = KX022A_REG_BUF_CLEAR,
>>> + .buf_status1 = KX022A_REG_BUF_STATUS_1,
>>> + .buf_read = KX022A_REG_BUF_READ,
>>> + .inc1 = KX022A_REG_INC1,
>>> + .inc4 = KX022A_REG_INC4,
>>> + .inc5 = KX022A_REG_INC5,
>>> + .inc6 = KX022A_REG_INC6,
>>> + .xout_l = KX022A_REG_XOUT_L,
>>> +};
>>> +EXPORT_SYMBOL_NS_GPL(kx022a_chip_info, IIO_KX022A);
>>
>> Do you think the fields (or at least some of them) in this struct could be
>> named based on the (main) functionality being used, not based on the
>> register name? Something like "watermark_reg", "buf_en_reg", "reset_reg",
>> "output_rate_reg", "int1_pinconf_reg", "int1_src_reg", "int2_pinconf_reg",
>> "int1_src_reg" ...
>>
>> I would not be at all surprized to see for example some IRQ control to be
>> shifted from INC<X> to INC<Y> or cntl<X> / buf_cntl<X> stuff to be moved to
>> cntl<Y> or to buf_cntl<Y> for next sensor we want to support. Especially
>> when new cool feature is added to next sensor, resulting also adding a new
>> cntl<Z> or buf_cntl<Z> or INC<Z>.
>>
>> I, however, believe the _functionality_ will be there (in some register) -
>> at least for the ICs for which we can re-use this driver. Hence, it might be
>> nice - and if you can think of better names for these fields - to rename
>> them based on the _functionality_ we use.
>>
>> Another benefit would be added clarity to the code. Writing a value to
>> "buf_en_reg", "watermark_reg" or to "int1_src_reg" is much clearer (to me)
>> than writing a value to "buf_cntl1", "buf_cntl2" or "INC4". Especially if
>> you don't have a datasheet at your hands.
>>
>> I am not "demanding" this (at least not for now :]) because it seems these
>> two Kionix sensors have been pretty consistent what comes to maintaining the
>> same functionality in the registers with same naming - but I believe this is
>> something that may in any case be lurking around the corner.
>
> I agree, this seems to be the better solution. I will look into this.
>

Thanks for going the extra mile :)

Yours,
-- Matti

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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