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.