Hi Ramesh, On Tuesday 11 Apr 2017 12:19:54 Ramesh Shanmugasundaram wrote: > > On Tuesday 11 Apr 2017 09:57:45 Ramesh Shanmugasundaram wrote: > >>> On Tuesday 07 Feb 2017 15:02:32 Ramesh Shanmugasundaram wrote: > >>>> Add device tree binding documentation for MAX2175 Rf to bits tuner > >>>> device. > >>>> > >>>> Signed-off-by: Ramesh Shanmugasundaram > >>>> <ramesh.shanmugasunda...@bp.renesas.com> > >>>> --- > >>>> .../devicetree/bindings/media/i2c/max2175.txt | 61 +++++++++++++ > >>>> .../devicetree/bindings/property-units.txt | 1 + > >>>> 2 files changed, 62 insertions(+) > >>>> create mode 100644 > >>>> > >>>> Documentation/devicetree/bindings/media/i2c/max2175.txt > >>>> diff --git > >>>> a/Documentation/devicetree/bindings/media/i2c/max2175.txt > >>>> b/Documentation/devicetree/bindings/media/i2c/max2175.txt new file > >>>> mode 100644 index 0000000..f591ab4 > >>>> --- /dev/null > >>>> +++ b/Documentation/devicetree/bindings/media/i2c/max2175.txt > > > > [snip] > > > >>>> +- maxim,am-hiz : empty property indicates AM Hi-Z filter > >>>> path is > >>>> + selected for AM antenna input. By default this > >>>> + filter path is not used. > >>> > >>> Isn't this something that should be selected at runtime through a > >>> control ? Or does the hardware design dictate whether the filter has > >>> to be used or must not be used ? > >> > >> This is dictated by the h/w design and not selectable at run-time. > >> I will update these changes in the next patchset. > > > > In that case I'm fine with a property, but could we name it in such a way > > that it describes the hardware instead of instructing the software on how > > to configure the device ? For instance (and this is a made-up example as I > > don't know exactly how this works), if the AM Hi-Z filter is required when > > dealing with AM frequencies and forbidden when dealing with other > > frequency bands, and *if* boards have to be designed specifically for one > > frequency band (AM, FM, VHF, L, ...) without any way to accept different > > bands, then you could instead use > > > > maxim,frequency-band = "AM"; > > > > and enable the filter accordingly in the driver. This would be in my > > opinion a better system hardware description. > > I am not sure. The AM antenna input path has a default filter and AM Hi-Z > filter. H/W dictates the path to be used for AM input only and this is > fixed. The device can be configured to use different bands at runtime & not > AM only. I could edit the description as below: > > - maxim,am-hiz : empty property indicates AM Hi-Z filter path > usage for AM antenna input as dictated by hardware design. By default this > filter path is not used. > > Is it any better? Do you still think the property name should be changed > please?
I still think this should be renamed, but possibly because I don't understand all the details of this particular feature :-). The property, as named and documented above, describes a software features. It requests the driver to enable the AM Hi-Z filter. DT properties should instead describe the hardware. You should use a property that describes the hardware design, and use that to infer, in the driver, whether to enable or disable the filter. -- Regards, Laurent Pinchart
