Re: [PATCH 1/2] iio: accel: bma180: Fix BMA25x bandwidth register values

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 26 May 2021 14:12:02 +0200
Linus Walleij <linus.walleij@linaro.org> wrote:

> On Wed, May 26, 2021 at 11:44 AM Stephan Gerhold <stephan@gerhold.net> wrote:
> 
> > According to the BMA253 datasheet [1] and BMA250 datasheet [2] the
> > bandwidth value for BMA25x should be set as 01xxx:
> >
> >   "Settings 00xxx result in a bandwidth of 7.81 Hz; [...]
> >    It is recommended [...] to use the range from ´01000b´ to ´01111b´
> >    only in order to be compatible with future products."
> >
> > However, at the moment the drivers sets bandwidth values from 0 to 6,
> > which is not recommended and always results into 7.81 Hz bandwidth
> > according to the datasheet.
> >
> > Fix this by introducing a bw_offset = 8 = 01000b for BMA25x,
> > so the additional bit is always set for BMA25x.
> >
> > [1]: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bma253-ds000.pdf
> > [2]: https://datasheet.octopart.com/BMA250-Bosch-datasheet-15540103.pdf
> >
> > Cc: Peter Meerwald <pmeerw@pmeerw.net>
> > Cc: Linus Walleij <linus.walleij@linaro.org>
> > Fixes: 2017cff24cc0 ("iio:bma180: Add BMA250 chip support")
> > Signed-off-by: Stephan Gerhold <stephan@gerhold.net>  
> 
> Good catch!
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Applied to the fixes-togreg branch of iio.git and marked for stable.

I think I can probably get away with picking up patch 2 into the togreg branch
without anything blowing up during the merge.

Thanks,

Jonathan

> 
> > After spending some more time with the driver I noticed that BMA253/BMA254
> > would actually be better supported by the bmc150-accel driver (which
> > doesn't have this problem and also supports the motion trigger/interrupt).
> >
> > I'm preparing a separate patch set to move BMA254 to bmc150-accel at least,
> > but I'm not sure about BMA250 so this patch is relevant anyway. And I had
> > it almost done already, so I thought it's better to send it. :)  
> 
> I looked at the preliminary patches and this looks really good
> too.
> 
> Yours,
> Linus Walleij