Re: [PATCH] clk: si570: Add a driver for SI570 oscillators

[Guenter Roeck <linux@roeck-us.net>]

On Mon, Sep 16, 2013 at 12:37:43PM -0600, Stephen Warren wrote:
> On 09/16/2013 11:35 AM, Guenter Roeck wrote:
> > On Mon, Sep 16, 2013 at 10:59:58AM -0600, Stephen Warren wrote:
> >> On 09/16/2013 10:49 AM, Guenter Roeck wrote:
> >>> On Mon, Sep 16, 2013 at 10:34:28AM -0600, Stephen Warren wrote:
> >>>> On 09/12/2013 06:55 PM, Soren Brinkmann wrote:
> >>>>> Add a driver for SILabs 570, 571, 598, 599 programmable oscillators.
> >>>>> The devices generate low-jitter clock signals and are reprogrammable via
> >>>>> an I2C interface.
> ...
> >>>>> +Optional properties:
> >>>>> + - initial-fout: Initial output frequency to set during probe
> >>>>
> >>>> "probe" is a Linux-specific concept. This property should be removed. If
> >>>> the driver is asked to set a specific frequency, it should do so, but I
> >>>> don't think it should program something pro-actively just because it
> >>>> starts up.
> >>>>
> >>>> If this property is acceptable, it'd be better to describe it more along
> >>>> the lines of the following:
> >>>>
> >>>> initial-fout: The frequency at which the system requires the clock to
> >>>> operate.
> >>>
> >>> It should probably be something like "clock-frequency". In many use cases
> >>> the programmed frequency is set to a constant frequency at system startup
> >>> and never changed, similar to other clocks.
> >>
> >> I was going to suggest that too, but re-considered since I think
> >> clock-frequency is more appropriate for fixed-frequency clocks, rather
> >> than to specify the value at which a programmable clock generator should
> >> operate?
> >>
> >> I don't think we have a good story yet for how to represent
> >> how-we-want-the-clock-tree-configured, as opposed to representing the HW
> >> itself (which is what DT should be more about).
> >
> > In many cases the chip _is_ used to generate a fixed frequency, so we will
> > have to have a means to describe it. That it _can_ be used differently is a
> > different matter. After all, that is true for many clock generators.
> 
> Perhaps if clock-frequency is specified, the driver should refuse to
> provide anything else. If clock-frequency isn't specified, the driver
> shouldn't touch the HW when it initializes, but should honor any
> requests that come in from other drivers? That would maintain what I
> feel is clock-frequency's connection to being a fixed clock.
> 
Ok with me, if that is in line with other clock drivers.

Guenter