Re: [PATCH v3 7/7] iio: accel: Add support for Kionix/ROHM KX132-1211 accelerometer

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 7 May 2023 16:56:55 +0200
Mehdi Djait <mehdi.djait.k@gmail.com> wrote:

> Hello Jonathan,
> 
> On Sat, May 06, 2023 at 05:46:51PM +0100, Jonathan Cameron wrote:
> > On Fri, 5 May 2023 20:11:33 +0200
> > Mehdi Djait <mehdi.djait.k@gmail.com> wrote:
> >   
> > > Hello Jonathan,
> > > 
> > > On Mon, May 01, 2023 at 03:56:45PM +0100, Jonathan Cameron wrote:  
> > > > On Tue, 25 Apr 2023 00:22:27 +0200
> > > > Mehdi Djait <mehdi.djait.k@gmail.com> wrote:
> > > >     
> > > > > Kionix KX132-1211 is a tri-axis 16-bit accelerometer that can support
> > > > > ranges from ±2G to ±16G, digital output through I²C/SPI.
> > > > > Add support for basic accelerometer features such as reading acceleration
> > > > > via IIO using raw reads, triggered buffer (data-ready), or the WMI IRQ.
> > > > > 
> > > > > Datasheet: https://kionixfs.azureedge.net/en/document/KX132-1211-Technical-Reference-Manual-Rev-5.0.pdf
> > > > > Signed-off-by: Mehdi Djait <mehdi.djait.k@gmail.com>    
> > > > 
> > > > Two tiny things inline.  
> > > >     
> > > > > +static int kx132_get_fifo_bytes(struct kx022a_data *data)
> > > > > +{
> > > > > +	struct device *dev = regmap_get_device(data->regmap);
> > > > > +	__le16 buf_status;
> > > > > +	int ret, fifo_bytes;
> > > > > +
> > > > > +	ret = regmap_bulk_read(data->regmap, data->chip_info->buf_status1,
> > > > > +			       &buf_status, sizeof(buf_status));
> > > > > +	if (ret) {
> > > > > +		dev_err(dev, "Error reading buffer status\n");
> > > > > +		return ret;
> > > > > +	}
> > > > > +
> > > > > +	fifo_bytes = le16_to_cpu(buf_status);
> > > > > +	fifo_bytes &= data->chip_info->buf_smp_lvl_mask;    
> > > > 
> > > > Slight preference for FIELD_GET() as it saves me checking the mask includes
> > > > lowest bits.    
> > > 
> > > This will mean I have the remove the chip_info member buf_smp_lvl_mask
> > > and use KX132_MASK_BUF_SMP_LVL directly because otherwise the
> > > __builtin_constant_p function will cause an error when building. 
> > > Check: https://elixir.bootlin.com/linux/latest/source/include/linux/bitfield.h#L65
> > > 
> > > I can change it to FIELD_GET() if you want to.  
> > 
> > Good point.  You could use le16_get_bits() though which I'm fairly sure will take
> > a variable just fine.
> >   
> 
> I don't think it will work. 
> 
> From the commit log introducing the {type}_get_bits to <linux/bitfield.h>
> "    Field specification must be a constant; __builtin_constant_p() doesn't
>     have to be true for it, but compiler must be able to evaluate it at
>     build time.  If it cannot or if the value does not encode any bitfield,
>     the build will fail. "
> 
> Actually Geert Uytterhoeven tried to solve excatly this issue, but it
> seems that the patch was not accepted. 
> Check: https://lore.kernel.org/linux-iio/3a54a6703879d10f08cf0275a2a69297ebd2b1d4.1637592133.git.geert+renesas@glider.be/
> 
> 
> So which solution would be the best:
> 
> 1. Use directly KX132_MASK_BUF_SMP_LVL, the only reason I was trying to
> avoid this was to make this function generic enough for other chip
> variants
> 
> 2. Copy the field_get() definition from drivers/clk/at91 or from the commit
> of Geert and use it in this driver
> 
> 3. leave it as it is ? 
This fine.  Sorry for the diversion to nowhere!

Jonathan

> 
> 4. another solution ?
> 
> > >  
> > > > 
> > > >     
> > > > > +
> > > > > +	return fifo_bytes;
> > > > > +}
> > > > > +
> > > > >  static int __kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples,
> > > > >  			       bool irq)
> > > > >  {
> > > > > @@ -1036,6 +1157,32 @@ const struct kx022a_chip_info kx022a_chip_info = {
> > > > >  };
> > > > >  EXPORT_SYMBOL_NS_GPL(kx022a_chip_info, IIO_KX022A);
> > > > >  
> > > > > +const struct kx022a_chip_info kx132_chip_info = {
> > > > > +	.name		  = "kx132-1211",
> > > > > +	.regmap_config	  = &kx132_regmap_config,
> > > > > +	.channels	  = kx132_channels,
> > > > > +	.num_channels	  = ARRAY_SIZE(kx132_channels),
> > > > > +	.fifo_length	  = KX132_FIFO_LENGTH,
> > > > > +	.who		  = KX132_REG_WHO,
> > > > > +	.id		  = KX132_ID,
> > > > > +	.cntl		  = KX132_REG_CNTL,
> > > > > +	.cntl2		  = KX132_REG_CNTL2,
> > > > > +	.odcntl		  = KX132_REG_ODCNTL,
> > > > > +	.buf_cntl1	  = KX132_REG_BUF_CNTL1,
> > > > > +	.buf_cntl2	  = KX132_REG_BUF_CNTL2,
> > > > > +	.buf_clear	  = KX132_REG_BUF_CLEAR,
> > > > > +	.buf_status1	  = KX132_REG_BUF_STATUS_1,
> > > > > +	.buf_smp_lvl_mask = KX132_MASK_BUF_SMP_LVL,    
> > > > 
> > > > There are some things in here (typically where the define isn't used
> > > > anywhere else) where I think it would be easier to follow if the
> > > > value was listed here.  Masks and IDs for example. 
> > > >     
> > > 
> > > After removing buf_smp_lvl_mask, which members will be easier to understand (besides id) ?   
> > 
> > I haven't gone through them.  Length seems an obvious one.  It's a number not a magic value.
> > Register addresses might also be simpler if they aren't used elsewhere.
> > 
> > Not really about understanding just about a define that adds nothing if all we do is
> > assign it to a variable of the same name.  
> 
> Do you have a strong opinion about this ? 
> 
> I would really prefer to leave it like this, for the following reasons:
> 
> 1. If I directly use values here, I have to do it also in the previous
> patch where I introduce the chip_info for the kx022a -> this means I
> will have defines in the h file which are not used at all -> the defines should
> be deleted -> the patch will get unnecessarily bigger. I received
> multiple comments about removing unnecessary changes and reducing of the
> patch size when possible.
> 
> 2. Consistency: having all the defines in one place really seems to be
> better for understanding IMO. I find the mix of values and defines in 
> the chip-info a bit confusing, e.g., I will use the direct value for 
> KX132_REG_CNTL but not for KX132_REG_CNTL2 because KX132_REG_CNTL2 is
> referenced in a regmap_range. 
> 
> --
> Kind Regards
> Mehdi Djait