On Mon, 18 Nov 2019 00:25:04 +0000
Dan Robertson <dan@xxxxxxxxxxxxxxx> wrote:
> Sorry for the incredibly late reply. Before I submit the next patchset version,
> I have a question from the last set of reviews.
>
> On Mon, Oct 21, 2019 at 04:20:16PM +0100, Jonathan Cameron wrote:
> > On Sat, 19 Oct 2019 02:43:51 +0000
> > Dan Robertson <dan@xxxxxxxxxxxxxxx> wrote:
> > > On Fri, Oct 18, 2019 at 10:23:38AM +0300, Andy Shevchenko wrote:
> > > > On Fri, Oct 18, 2019 at 6:44 AM Dan Robertson <dan@xxxxxxxxxxxxxxx> wrote:
> > > > > +static const int bma400_osr_table[] = { 0, 1, 3 };
> > > >
> > > > > +/* See the ACC_CONFIG1 section of the datasheet */
> > > > > +static const int bma400_sample_freqs[] = {
> > > > > + 12, 500000,
> > > > > + 25, 0,
> > > > > + 50, 0,
> > > > > + 100, 0,
> > > > > + 200, 0,
> > > > > + 400, 0,
> > > > > + 800, 0,
> > > > > +};
> > > >
> > > > This can be replaced by a formula(s).
> > >
> > > Yeah I think I can implement the get, set, and read functions for sample_freq
> > > with a formula, but the scale and sample frequency tables are needed by the
> > > implementation of read_avail. A implementation of read_avail with a range and
> > > a step would be ideal, but I couldn't find any documentation on implementing
> > > read_avail where the step value of the range is a multiple. Please correct
> > > me if I've missed something.
> >
> > Indeed. We've only defined it as being fixed intervals.
> > I'm not keen to expand the options for the userspace interface any
> > further.
> >
> > You could compute the values at startup and store it in your state structure
> > I think (or compute them on demand, but you'd need to have the space somewhere
> > non volatile).
> >
>
> I ended up writing an implementation that uses a formula for the get/set
> functions of the sample frequency and scale, but uses a table for the
> implementation of the read_avail function. While it does work, I worry
> that this makes the driver less maintainable and would make it harder to
> add support for a new hypothetical future BMA4xx device. Also, the majority
> of drivers seem to use a table for the raw value to user input conversion,
> so a move from this might make the code less "familiar".
>
> If we do stick with the translation table, would it be better to have two
> tables (a translation table and a read_avail table) so that we do not have
> a step distance of two? This would mean we would need to maintain two
> tables, but would simplify the code.
If a function is your preferred route you could also just use it to compute
the values for the available table at startup?
Otherwise, its fine to just use a table for both.
>
> Random workflow question:
>
> The sampling ratio, frequency, etc code seems to be the most complicated part
> of the driver. Is it typically recommended to upstream a more minimal driver
> that might assume the defaults?
Often people upstream a first version that just uses defaults, then follow
up (if they care) with later series adding the more fiddly elements.
Sometimes those more fiddly bits never come as a particular author
never needed them. That's absolutely fine. It's a rare driver
that supports all the features on a non trivial device!
Thanks,
Jonathan
>
> Cheers,
>
> - Dan
>
