Re: [PATCH v3 2/7] dt-bindings: media: Add MAX2175 binding description

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Ramesh,

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.shanmugasundaram@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.

-- 
Regards,

Laurent Pinchart